Atoll RF Planning and Optimisation Software Version 2.7.1
AFP Reference Guide
AT271_ARG_E4
AFP Reference Guide
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Atoll 2.7.1 AFP Reference Guide Release AT271_ARG_E4
© Copyright 1997 - 2008 by Forsk The software described in this document is provided under a licence agreement. The software may only be used/copied under the terms and conditions of the licence agreement. No part of this document may be copied, reproduced or distributed in any form without prior authorisation from Forsk. The product or brand names mentioned in this document are trademarks or registered trademarks of their respective registering parties.
About AFP Reference Guide This document is aimed at frequency planning engineers using Atoll AFP module to perform automatic frequency planning of their networks. This document introduces the AFP with a high level description of the frequency planning process in Atoll. Then descending lower to the practical level, this document describes in detail every aspect of frequency planning in Atoll. Main topics covered in this document include AFP pre-requisites, AFP usage, AFP minimization target and some possible problems that may come up during training. This document begins with a basic user guide containing a short operational introduction to the AFP process in Atoll. Then it goes on to summarize most aspects of the practical planning process and provides detailed discussions on certain topics. It also explains the means to evaluate a frequency plan. Furthermore, a chapter is dedicated to advanced topics and troubleshooting in the end. The appendices describe the technical aspects of the cost function, the BSIC allocation al location algorithm, the IM calculation, and the dimensioning process.
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Table of Contents
Table of Contents
1
Overview ......................................................................................... 13
1.1 1.1.1 1.1.2
Introduction to AFP .......................................................................................................... ................................................................................................................................ ...................... 13 13 Frequency Assignment as a Cost Minimization Problem ................................................................. 13 ................................................................. 13 Abbreviations .................................................................................................................................... 13 .................................................................................................................................... 13
1.2
Architecture ............................................................................................................................................ ............................................................................................................................................ 14 14
2
Basic AFP Tutorial .......................................................................... 19
2.1 2.2 2.3 2.4 2.5 2.6 2.6.1 2.6.2 2.7 2.8 2.8.1 2.8.2
33.1 3.1.1 3.1.2 3.1.3 3.1.3.1 3.1.3.2 3.1.3.3 3.1.3.3.1 3.1.3.4 3.1.3.5 3.1.4 3.1.5 3.1.6 3.1.7 3.1.8 3.1.9 3.1.10 3.1.11 3.1.12 3.2 3.2.1 3.2.1.1 3.2.2
4 4.1 4.1.1 4.1.2 4.1.3 4.2 4.2.1 4.2.2 4.2.3 4.2.4 4.3 4.3.1 4.4
© Fo F orsk 2008
AFP Process in Atoll .................................................................................................................... .............................................................................................................................. .......... 19 19 Loading and Validating the Network ...................................................................................................... ...................................................................................................... 20 20 Definition of the AFP Scope ................................................................................................................... ................................................................................................................... 22 22 Preparing to Launch the AFP ................................................................................................................. 23 ................................................................................................................. 23 Launching the AFP and Monitoring its Progress .................................................................................... .................................................................................... 25 25 AFP Outputs........................................................................................................................................... ........................................................................................................................................... 27 27 Partial Commit Functionality ............................................................................................................. 29 ............................................................................................................. 29 Automatic Constraint Violation Resolution ....................................................................................... 30 ....................................................................................... 30 Visualising and Manipulating Results..................................................................................................... ..................................................................................................... 31 31 Manual Frequency Allocation ................................................................................................................. ................................................................................................................. 31 31 Manual Frequency Allocation for SFH Case .................................................................................... .................................................................................... 31 31 Manual Frequency Allocation for NH Case ...................................................................................... 31 ...................................................................................... 31
Fre anning Prerequisites .................................................. 35 35 Atq olu l Dean tacMyodP ell..................................................................................................................................... ..................................................................................................................................... 35 Reliability and Propagation ............................................................................................................... ............................................................................................................... 35 35 HCS Layers ...................................................................................................................................... 35 ...................................................................................................................................... 35 Subcells ............................................................................................................................................ ............................................................................................................................................ 36 36 Key Roles of Subcells ................................................................................................................. ................................................................................................................. 36 36 Concentric Cells and Dual-band Cells ........................................................................................ ........................................................................................ 36 36 Minimum C/I................................................................................................................................ ................................................................................................................................ 36 36 Quality Targets ...................................................................................................................... ...................................................................................................................... 36 36 Traffic Loads ............................................................................................................................... ............................................................................................................................... 36 36 Local Domain Restrictions .......................................................................................................... 37 .......................................................................................................... 37 TRXs ..................................................................................................................... ................................................................................................................................................ ........................... 37 37 Freezing Flags .................................................................................................................................. 37 .................................................................................................................................. 37 AFP Weights ...................................................................................................... .................................................................................................................................... .............................. 37 37 Spectrum Administration .................................................................................................................. .................................................................................................................. 37 37 Redundancy and Subcell Audit ........................................................................................................ ........................................................................................................ 37 37 Neighbour Importance ...................................................................................................................... ...................................................................................................................... 38 38 SeparationConstraints Table ............................................................................................................ ............................................................................................................ 38 38 SeparationRules Table and Rule Priority ......................................................................................... ......................................................................................... 38 38 Adjacency Suppression .................................................................................................................... .................................................................................................................... 38 38 AFP Performance Indicators .................................................................................................................. 38 .................................................................................................................. 38 AFP TRX Rank ................................................................................................................................. ................................................................................................................................. 38 38 TRX Rank Usage ........................................................................................................................ 39 ........................................................................................................................ 39 Total Cost and Separation Violation Cost Component ..................................................................... ..................................................................... 39 39
Frequency P Pllan O Op ptimisation. n........................................................... 43 Step 1 (Optional): Traffic Model Usage .................................................................................................. .................................................................................................. 43 43 Creating a Traffic Map Based only on Clutter Weighting ................................................................. ................................................................. 43 43 Performing a Traffic Capture ............................................................................................................ ............................................................................................................ 43 43 Creating IMs Based on Traffic .......................................................................................................... .......................................................................................................... 44 44 Step 2 (Optional): Neighbour Relations and Relative Weighting ........................................................... ........................................................... 44 44 Automatic Neighbour Allocation ....................................................................................................... 44 ....................................................................................................... 44 Importing Neighbour Importance ...................................................................................................... 45 ...................................................................................................... 45 Extending Existing Neighbour Relations .......................................................................................... .......................................................................................... 45 45 Importing Partial Sources of Neighbour Importance ........................................................................ ........................................................................ 46 46 Step 3 (Optional): Using Dimensioning .................................................................................................. .................................................................................................. 47 47 Optimal Dimensioning of an Existing Network ................................................................................. 47 ................................................................................. 47 Step 4: Optimal Usage of the Atoll AFP ................................................................................................. ................................................................................................. 48 48
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4.4.1 4.4.1.1 4.4.1.2 4.4.1.3 4.4.1.4 4.4.1.5 4.4.1.6 4.4.1.7 4.4.1.8 4.4.1.9 4.4.1.10 4.4.1.11 4.4.2 4.4.2.1 4.4.2.2 4.4.2.3 4.4.2.3.1 4.4.2.3.2 4.4.2.4
5
Introduction to the AFP Cost Function .............................................................................................. ..............................................................................................48 48 Combination o off Se Separation V Viiolation a an nd Interference P Prrobabilities ........................................... ...........................................48 48 Counting TRXs (Nodes) Instead of Relations (Edges) ................................................................ ................................................................48 48 Each TRX Cost............................................................................................................................ ............................................................................................................................49 49 Separation Violation Cost ............................................................................................................ ............................................................................................................49 49 Interference Cost ......................................................................................................................... .........................................................................................................................50 50 Probabilistic Cost Combination ................................................................................................... ...................................................................................................50 50 Missing TRX Cost ........................................................................................................................ ........................................................................................................................50 50 Corrupted TRX Cost ....................................................................................................................51 ....................................................................................................................51 Out-of-domain Frequency Assignment Cost ...............................................................................51 ...............................................................................51 Quality Target .............................................................................................................................. ..............................................................................................................................51 51 Modifiable and Non-Modifiable Costs .......................................................................................... ..........................................................................................51 51 Most Important Cost Function Parameters and Tuning .................................................................... ....................................................................52 52 Interference Weight vs. Separation Weight ................................................................................. .................................................................................52 52 Cost of Changing a TRX ..................................................................................................... ............................................................................................................. ........52 52 Quality Target and C/I Weighting ................................................................................................ ................................................................................................53 53 Quality Target ........................................................................................................................ ........................................................................................................................53 53 C/I Weighting ......................................................................................................................... .........................................................................................................................53 53 Separation Weights Settings ....................................................................................................... .......................................................................................................54 54
Means to Evaluate Frequency Plans... s...............................................57 .57
5.1 5.1.1 5.1.1.1 5.1.1.1.1 5.1.1.1.2 5.1.1.2 5.1.1.3 5.1.2
Estimating Frequency Plan Quality......................................................................................................... .........................................................................................................57 57 Using Interference Studies ................................................................................................................57 ................................................................................................................57 Various Interference Studies ....................................................................................................... .......................................................................................................57 57 TRX Based Interference Study ..............................................................................................57 ..............................................................................................57 Worst Case Interference Study.............................................................................................. ..............................................................................................58 58 Visualising TRX Ranks with a TRX Based Interference Study ....................................................58 ....................................................58 Visualising C/I Distributions with a TRX Based Interference Study ............................................. .............................................58 58 Using Audit ........................................................................................................................................ ........................................................................................................................................59 59
5.1.2.1 5.1.2.1.1 5.1.2.1.2
Global Separation Fitness Expression ........................................................................................ ........................................................................................59 59 Forsk Independent Separation Fitness Expression (FISFE) ................................................. .................................................59 59 Main Separation Violation Item Summary ............................................................................. .............................................................................59 59 Using Point Analysis ............................................................................................................................... ...............................................................................................................................60 60 Example 1: Combination of Interference Effects ...............................................................................61 ...............................................................................61 Example 2: Counting Strong Interference Only Once ....................................................................... .......................................................................61 61 Uniform Frequency Usage Distribution ................................................................................................... ...................................................................................................61 61 When Uniform Distribution and Quality do not Coincide ...................................................................62 ...................................................................62 Domain Range Effect and Adjacent Constraints .........................................................................62 .........................................................................62
5.2 5.2.1 5.2.2 5.3 5.3.1 5.3.1.1
6 6.1 6.1.1 6.1.2 6.1.3 6.1.4 6.1.5 6.1.6 6.1.7 6.1.8 6.1.9 6.1.9.1 6.1.10 6.1.11 6.1.11.1 6.2 6.2.1 6.2.1.1 6.2.1.2 6.3 6.4 6.5 6.6 6.6.1 6.6.2 6.6.3 6.7
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Advanced To Topics a an nd T Trroubleshooting ........................................... 65 Various AFP Related Features ............................................................................................................... ...............................................................................................................65 65 SFH (HSN, MAL, MAIO) ................................................................................................................... ...................................................................................................................65 65 Definition of Atom .............................................................................................................................. ..............................................................................................................................65 65 Synchronous Networks ..................................................................................................................... .....................................................................................................................65 65 Optimising Hopping Gains ........................................................................................................ ................................................................................................................ ........65 65 Fractional Load ................................................................................................................ ................................................................................................................................. .................65 65 Domain Use Ratio ............................................................................................................................. .............................................................................................................................66 66 User Defined MAL Length ................................................................................................................. .................................................................................................................66 66 HSN Allocation .................................................................................................................................. ..................................................................................................................................66 66 MAIO Allocation ................................................................................................................................ ................................................................................................................................66 66 Staggered MAIO Allocation ......................................................................................................... .........................................................................................................66 66 BSIC Allocation ................................................................................................................................. .................................................................................................................................66 66 Robustness of Atoll AFP ................................................................................................................... ...................................................................................................................67 67 Value Ranges and Limitations at Validation ................................................................................ ................................................................................67 67 Managing Consistency in Atoll and the AFP...........................................................................................68 ...........................................................................................68 Service Zone of a Subcell ................................................................................................................. .................................................................................................................68 68 Specifying Correct Interference Study Coverage Criteria ........................................................... ...........................................................68 68 Selecting “All servers” or “Best Server” Service Zone ................................................................. .................................................................69 69 Event Viewer...........................................................................................................................................69 ........................................................................................................................................... 69 Interference Study Quality Criteria .......................................................................................................... ..........................................................................................................69 69 Calculation Zone Border Effect ...............................................................................................................69 ...............................................................................................................69 Frequency Planning Techniques ............................................................................................................ ............................................................................................................70 70 Basics................................................................................................................................................ ................................................................................................................................................70 70 Post-processing of Hot Spots............................................................................................................70 ............................................................................................................70 Learning the Network and Solving for Hot Spots ..............................................................................70 ..............................................................................70 Performance and Memory Issues in Large GSM Projects...................................................................... ......................................................................70 70
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Table of Contents
7 7.1 7.2 7.3 7.4 7.4.1 7.4.1.1 7.4.1.2 7.4.1.3 7.4.2 7.5
8
8.1 8.1.1 8.1.2 8.1.3 8.1.3.1 8.1.3.2 8.1.4 8.2 8.2.1 8.2.2 8.2.3 8.2.4 8.2.4.1 8.2.4.2 8.2.4.3 8.2.5 8.3 8.3.1 8.3.2 8.3.3 8.3.4 8.4 8.4.1 8.4.2 8.4.3 8.4.3.1 8.4.3.2 8.4.3.2.1 8.4.3.2.2 8.4.3.2.3 8.4.3.3 8.4.4 8.4.4.1 8.4.4.2 8.4.4.3
© Fo F orsk 2008
Interference Matrices ...................................................................... 75 Types of Supported Interference Matrices ............................................................................................. ............................................................................................. 76 76 Interference Matrices Storage ................................................................................................................ ................................................................................................................ 76 76 Multiple File Import ................................................................................................................................. ................................................................................................................................. 77 77 Maximum Likelihood Combination ......................................................................................................... ......................................................................................................... 77 77 Scope and Context of Interference Matrices .................................................................................... 77 .................................................................................... 77 Interference Matrix Context ........................................................................................................ ........................................................................................................ 77 77 Interference Matrix Scope........................................................................................................... ........................................................................................................... 79 79 Keeping the Scope and Context Up to Date ............................................................................... ............................................................................... 80 80 Interference Matrix Combination in Atoll AFP Module ...................................................................... 80 ...................................................................... 80 Interference Matrix Calculation .............................................................................................................. .............................................................................................................. 81 81
Appendices ..................................................................................... 85 Appendix 1: Description of the AFP Cost Function ................................................................................ ................................................................................ 85 85 Notations .......................................................................................................................................... .......................................................................................................................................... 85 85 Cost Function ................................................................................................................................... ................................................................................................................................... 85 85 Cost Components ............................................................................................................................. ............................................................................................................................. 87 87 Separation Violation Cost Component........................................................................................ ........................................................................................ 87 87 Interference Cost Component..................................................................................................... ..................................................................................................... 88 88 I_DIV, F_DIV and Other Advanced Cost Parameters ...................................................................... ...................................................................... 90 90 Appendix 2: Interferences ...................................................................................................................... ...................................................................................................................... 91 91 Using Interferences .......................................................................................................................... .......................................................................................................................... 91 91 Cumulative Density Function of C/I Levels ....................................................................................... ....................................................................................... 91 91 Precise Definition . ....................................................................................................... ............................................................................................................................ ...................... 91 91 Precise Interference Distribution Strategy ........................................................................................ ........................................................................................ 92 92 Direct Availability of Precise Interference Distribution to the AFP .............................................. .............................................. 92 92 Efficient Calculation and Storage of Interference Distribution .................................................... .................................................... 92 92 Robustness of the IM .................................................................................................................. .................................................................................................................. 92 92 Traffic Load and Interference Information Discrimination ................................................................. 92 ................................................................. 92 Appendix 3: BSIC Allocation .................................................................................................................. .................................................................................................................. 94 94 Definitions ......................................................................................................................................... ......................................................................................................................................... 94 94 Hard Criterion ................................................................................................................................... ................................................................................................................................... 94 94 Soft Criterion ...................................................................................................... .................................................................................................................................... .............................. 94 94 Behaviour ......................................................................................................................................... ......................................................................................................................................... 94 94 Appendix 4: Traffic Capture and Dimensioning...................................................................................... ...................................................................................... 95 95 Introduction ....................................................................................................................................... ....................................................................................................................................... 95 95 Traffic Map Generation ..................................................................................................................... ..................................................................................................................... 95 95 Traffic Capture Process .................................................................................................................... .................................................................................................................... 95 95 Inputs .......................................................................................................................................... 95 .......................................................................................................................................... 95 The Engine ....................................................................................................................... ................................................................................................................................. .......... 96 96 Traffic Distribution ................................................................................................................. ................................................................................................................. 96 96 Average Timeslot Capacity ................................................................................................... ................................................................................................... 97 97 Integration ............................................................................................................................. ............................................................................................................................. 97 97 Outputs ....................................................................................................................................... ....................................................................................................................................... 98 98 Network Dimensioning Process ....................................................................................................... 99 ....................................................................................................... 99 Inputs .......................................................................................................................................... .......................................................................................................................................... 99 99 Dimensioning .............................................................................................................................. .............................................................................................................................. 99 99 Outputs ....................................................................................................................................... ....................................................................................................................................... 99 99
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List of Figures
List of Figures
Figur Fig ure e 2. 2.1: 1: Figure Figur e 2. 2.2: 2: Figur Fig ure e 2.3 2.3:: Fi Figu gure re 2. 2.4: 4:
AF AFP P Proc Proces ess s in A Ato toll.... ll...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... In Inte tera ract ction ion of the the AF AFP P with with Othe Otherr El Elem emen ents. ts... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .. AF AFP P Output Outputs s .. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... ..... ..... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... AF AFP P Laun Launch ch Wi Wiza zard rd - AF AFP P Sess Sessio ion n Tab.. Tab.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... ..
19 19 20 20
Figure Figur e 2. 2.5: 5: Fi Figur gure e 2. 2.6: 6: Fi Figu gure re 2. 2.7: 7: Fi Figu gure re 2. 2.8: 8: Fi Figu gure re 2. 2.9: 9: Figur Fig ure e 2. 2.10 10:: Fi Figu gure re 2. 2.11 11:: Fi Figu gure re 2. 2.12 12:: Figur Fig ure e 2. 2.13 13:: Fi Figu gure re 2. 2.14 14:: Figur Fig ure e 2. 2.15 15:: Fi Figu gure re 2. 2.16 16:: Figur Fig ure e 2. 2.17 17:: Figur Fig ure e 2. 2.18 18:: Fi Figu gure re 2. 2.19 19:: Fi Figu gure re 2. 2.20 20::
AF AFP P Laun Launch ch Wi Wiza zard rd - Sepa Separa rati tion ons s Ta Tab b .. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... ..... ..... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... AF AFP P Laun Launch ch Wi Wiza zard rd - Glob Global al Para Parame mete ters rs Ta Tab b .... ...... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... ..... ..... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Ev Even entt Vi View ewer er - Samp Sample le Me Mess ssag ages.. es.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... Mess Messag age e 1 .. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Mess Messag age e 2 .. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... AF AFP P Launc Launch h Wi Wind ndow ow .. .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Pa Part rtia iall Int Inter erfe fere renc nce e Mat Matri rice ces s - Repo Report.. rt.... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... Comp Comple lete te In Inte terf rfer eren ence ce M Mat atri rice ces s - Rep Repor ort.. t.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... AF AFP P Pr Prog ogre ress ss Wi Wind ndow. ow... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... Ev Even entt V View iewer er Me Mess ssag age e-S Sol olut ution ion Kept Kept .. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .. AF AFP P Pr Prog ogre ress ss Wi Wind ndow. ow... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... Cost Cost Dis Distr trib ibut utio ions ns on Fre Frequ quen enci cies.. es.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... Freq Freque uenc ncy y Usag Usage e Di Dist stri ribu buti tion ons.. s.... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... AF AFP P Resu Result lts s Wi Wind ndow... ow..... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Se Sepa para rati tion on C Con onst stra rain intt Vi Viol olat atio ion n De Deta tail ils s Me Mess ssag age.. e.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .. AF AFP P Res Resul ults ts Wi Wind ndow ow - Part Partia iall Co Comm mmit it F Fea eatu ture.. re.... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... ..
20 21 21 22 22 23 23 24 25 25 26 27 27 28 28 29
Fi Figu gure re 2. 2.21 21:: Fi Figu gure re 2. 2.22 22:: Fi Figu gure re 2. 2.23 23:: Fi Figu gure re 2. 2.24 24:: Fi Figu gure re 3. 3.1: 1: Fi Figu gure re 4. 4.1: 1: Fi Figu gure re 4. 4.2: 2: Fi Figu gure re 4. 4.3: 3: Fi Figu gure re 4. 4.4: 4: Fi Figu gure re 4. 4.5: 5: Fi Figu gure re 4. 4.6: 6: Fi Figu gure re 4. 4.7: 7: Fi Figu gure re 4. 4.8: 8: Fi Figu gure re 5. 5.1: 1: Fi Figu gure re 5. 5.2: 2:
AF AFP P Res Resul ults ts Wi Wind ndow ow - Part Partia iall Co Comm mmit it F Fea eatu ture.. re.... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .. Cons Constr trai aint nt Vio Violat latio ion n Reso Resolu luti tion on Too Tool.. l.... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... Sc Scan annin ning g for for Fr Freq eque uenc ncie ies... s..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Sc Scan annin ning g for for Fr Freq eque uenc ncie ies... s..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Mode Modell St Stan anda dard rd Devi Deviat atio ion n - Defa Defaul ultt Va Valu lue.. e.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .. Au Auto toma mati tic c Nei Neigh ghbo bour ur A All lloc ocat atio ion.. n.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... Au Auto toma mati tic c Nei Neigh ghbo bour ur Al Allo loca cati tion on Resu Result lts.. s.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ...... ..... .... .... .... .... Neig Neighb hbou ours rs Ta Tabl ble e .. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... Dime Dimens nsio ioni ning ng Pr Proc oces ess s .. .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... At Atoll oll AF AFP P Mo Modu dule le Pr Prop oper erti ties es - Sepa Separa rati tion on Weig Weight hts s Tab... Tab..... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .. At Atoll oll AF AFP PM Mod odule ule Pr Prope opert rties ies - Cost Cost Tab... Tab..... .... .... .... .... .... ..... ..... .... .... .... ..... ..... .... .... .... ..... ..... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... ..... ...... ...... ..... .... .... .... .... C/I C/I We Weig ight htin ing g .. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .. At Atoll oll AF AFP P Mo Modu dule le Pr Prop oper erti ties es - Sepa Separa rati tion on Weig Weight hts s Tab... Tab..... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .. In Inte terf rfer eren ence ce St Stud udy y Re Repo port. rt... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... TR TRX XB Bas ased ed Inte Interf rfer eren ence ce St Stud udies... ies..... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... ....
30 31 32 32 35 45 46 46 47 49 52 53 54 57 58
Fi Figu gure re 5. 5. 5.3: 3: Fi Figu gure re 5.4: 4: Fi Figu gure re 5. 5.5: 5: Fi Figu gure re 5. 5.6: 6: Fi Figu gure re 5. 5.7: 7: Fi Figu gure re 5. 5.8: 8: Fi Figu gure re 6. 6.1: 1: Fi Figu gure re 7. 7.1: 1: Fi Figu gure re 7. 7.2: 2: Fi Figu gure re 7. 7.3: 3: Fi Figu gure re 7. 7.4: 4: Fi Figur gure e 8. 8.1: 1: Fi Figu gure re 8. 8.2: 2: Fi Figu gure re 8. 8.3: 3: Fi Figur gure e 8. 8.4: 4: Fi Figu gure re 8. 8.5: 5:
TR TRX X Ba Base sed d Inte In terf rfer eren ence ce St Stud udy y.... - .... C/I C/ I .... Dist Di stri ribu buti tion ons s .... ..... ....... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... ..... ...... .... Ev Even ent tV Vie iewe wer rM Mes essa sage ges s .. .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... ..... Ev Even entt V Vie iewe werr M Mes essa sage ge 1... 1..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... Ev Even entt V Vie iewe werr M Mes essa sage ge 2... 2..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... Comb Combin inat atin in of Inte Interf rfer eren ence ce Ef Effe fect cts s .. .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ...... ..... Coun Counti ting ng St Stro rong ng Inte Interf rfer eren ence ce Only Only Once. Once... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ...... ..... Hopp Hoppin ing gS Seq eque uenc nce e Nu Numb mber ers. s.... ...... ..... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... In Inte terf rfer eren ence ce Ma Matr trix ix Pr Prop oper erti ties es Dial Dialog og - Gene Genera rall Ta Tab b .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .. In Inte terf rfer eren ence ce Ma Matr trix ix Pr Prop oper erti ties es Dial Dialog og - Adva Advanc nced ed Ta Tab... b..... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... In Inte terf rfer eren ence ce M Mat atri rix x Sc Scop ope.. e.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... AF AFP P Inte Interf rfer eren ence ce Ma Matr tric ices es Para Parame mete ters rs .. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .. At Atoll oll AF AFP P Mo Modu dule le Pr Prop oper erti ties es - Adva Advanc nced ed Ta Tab b .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... ..... ..... The The cum cumul ulat ativ ive ed den ensi sity ty of C/ C/II lev level els s bet betwe ween en [TX1 [TX1,, BCC BCCH] H] and and [TX [TX2, 2, BC BCCH CH]] .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Tr Traf affic fic M Map aps s Ove Overl rlay. ay... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... Tr Traf affii fiic c Over Overfl flow.. ow.... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... In Intr traa-La Laye yerr Dis Distr trib ibut utio ion n .. .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ....
59 60 60 60 61 61 66 78 78 79 81 90 91 96 97 97
Fi Figu gure re 8. 8.6: 6: Fi Figu gure re 8. 8.7: 7:
Tr Traf affi fic c Dist Distrib ribut utio ion n in At Atol olll ... ...... ..... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .. 98 Netw Networ ork kD Dim imen ensi sion oning ing Pr Proc oces ess... s..... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ...... ..... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..... ..... 99
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Overview This document describes every aspect of frequency planning in Atoll, from high level description of the frequency planning process to the practical level detail. Main topics covered in this document include AFP prerequisites, AFP usage, AFP minimisation target and some possible problems that may come up during training. This document begins with a basic user guide, a short operational introduction to the AFP process in Atoll, and goes on to summarize most aspects of the practical planning process with detailed discussions on certain topics. It also explains the means to evaluate a frequency plan available in Atoll. A chapter is dedicated to advanced topics and troubleshooting in the end. Four appendices contain in-depth information on technical aspects of the cost function, the BSIC allocation algorithm, the IM calculation and the dimensioning process respectively. All in all, this document is almost self sufficient with respect to the use of Atoll AFP.
1.1
Introduction to AFP The main role of an Automatic Frequency Planner (AFP) is to assign frequencies (channels) to the network such that the overall network quality is optimised. With the evolution of GSM over the years to integrate many improvements, additional requirements have emerged in the process of radio network planning. The implementation of baseband and synthesised frequency hopping, discontinous transmission and network synchronisation, for example, has led to higher sophistication in the process of frequency planning. These enhancements require that an AFP also be intelligent and advanced enough to help the frequency planner through out his tedious task. The Atoll AFP considers a large number of constraints and directives; for example, ARFCN separation requirements between transmitters, interference relations, HSN assignment methods, frequency domain constraints, a certain fractional load to maintain etc. Hence, the AFP depends on a variety of input data, such as the interference matrix, neighbourhood relations, traffic information and so on. This document not only explains how to use the Atoll AFP, A FP, by describing the AFP GUI, but also includes detailed descriptions of the various constraints, directives, di rectives, and data sources. The primary target of this document is to explain the technical background of the AFP.
1.1.1
Frequency Assignment as a Cost Minimization Problem From the technical point of view, the Frequency Assignment Problem (FAP) is considered as a minimization problem. This means that the AFP will generate a set of Frequency Plans (FPs), and propose the one that has the lowest cost as the “Best Solution”. Therefore, the AFP cost is the equivalent of AFP quality estimation: the lower the cost, the better should be the quality from the AFP point of view. The approach of cost minimization is not only the most common approach to the FAP but probably also the easiest to understand and control. It provides the user with means of guiding the AFP in its task. For example, by setting the co st of interference violation low, the AFP will concentrate its efforts on resolving the separation violations. There are AFP tools in which certain types of objectives are presented as “hard constraints”. If a hard constraint is not satisfied, the AFP does not offer any solution or offers a partial solution (with fewer frequencies and satisfying hard constraints). The philosophy of hard constraints vs. soft constraints has nothing to do with the quality of an AFP engine, it is merely a behaviour convention. In Atoll, we prefer always offering a solution to offering partial assignments or violating domain limitations. This ensures that you will always get a result when you launch the Atoll AFP. This result will very well depict the difficulty of the FAP. The cost of this solution will clearly indicate if unacceptable violations have occurred or if this plan has improved the current frequency plan. The cost function definition permits you to place as much emphasis as required on certain elements of the cost function. This manipulation will make the AFP behave as if it were guided by hard constraints, from the optimisation viewpoint, while retaining its property of being a quality monitor and a hardness-of-assignment monitor both.
1.1.2
Abbreviations Some abbreviations and terminologies used in the document are listed below:
© Fo F orsk 2008
GSM
Global System for Mobile Communications (Groupe ( Groupe Speciale Mobile) Mobile)
GPRS
General Packet Radio Service
EDGE
Enhanced Data rates for GSM (or Global) Evolution
EGPRS
EDGE based GPRS
TSL
Timeslot
TX
Transmitter or sector
TRX
Transceiver
BCCH
Broadcast Control CHannel. A term usually employed in Atoll to refer to the TRX carrying this channel.
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1.2
TCH
Traffic CHannel. A term usually employed in Atoll to refer to a TRX carrying traffic with usually the same coverage area as the BCCH.
TCH_INNER
Inner Traffic CHannel. A term usually employed in Atoll to refer to a TRX carrying traffic but usually having a coverage area less than that of a TCH.
HR/FR
Half Rate/Full Rate
CS
Circuit-switched
PS
Packet-switched
HCS
Hierarchical Cell Structure
Subcell
An entity defined by the pair [TX, TRX Type]
HO
Handover
kbps
Kilobits per second
GoS
Grade of Service
QoS
Quality of Service
KPI
Key Performance Indicators
TL
Traffic Load
P
Probability
C
Carrier power (Signal strength)
C/I
Carrier to Interference ratio
AFP
Automatic Frequency Planner/Planning
DTX
Discontinuous transmission
GUI
Graphical User Interface
FP
Frequency Plan
BBH SFH
Baseband Hopping Synthesized Hopping
NH
No Hopping
MAL
Mobile Allocation List. In the context of SFH, MAL is the group of frequencies used by the frequency hopping TRX.
AMR
Adaptive Multi-Rate
CC
Concentric Cells
Transmitter
Atoll synonym for cell or sector in conventional GSM jargon
FER
Frame Erasure Rate
FH
Frequency Hopping
DLPC
Down Link Power Control
RRM
Radio Resource Management
Synchronised transmitters
Transmitters that are synchronised and can, therefore, share the same HSN.
Data Model
A project can be saved in a filename.ATL file or as a database. In both cases, most of the project’s information is saved in database tables. We refer to these tables as the data model.
IM, IMco, IMadj
Interference Matrix, Co-channel / Adjacent-channel Interference Matrix
FN
Frame Number
CDF
Cumulative Density Function
TSC
Training Sequence Code
FAP
Frequency Assignment Problem
#
Number of
Architecture The Atoll Automatic Frequency Planning (AFP) module is an optional module that enables you to generate frequency plans for GSM and TDMA networks automatically. The Atoll AFP module can allocate the following parameters: • • • •
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Frequencies Fr Freq eque uenc ncy y hop hoppi ping ng grou groups ps (M (MAL AL)) HSN, MAIO BSIC BSIC (TSC (TSC plann lannin ing) g)
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TRX rank rank (ca (can n be use used d to pr priori ioritis tise e the us use e of good good freque frequenci ncies) es) Perfor Performan mance ce Indi Indicat cators ors at S Site ite/Ce /Cell/T ll/TRX RX lleve evels ls
Atoll works with an open AFP interface. Any AFP built using this interface can be able to allocate the following additional parameters. Future versions of the Atoll AFP module are planned to assign the following parameters as well: • • •
Group Group ID (be (bette tterr admi adminis nistra tratio tion n of the fr frequ equenc ency y reso resourc urces) es) TN offsets FN offsets
Atoll AFP implements simulated annealing, taboo search, graph heuristic heuristics s and machine learning. It manages its time resources to match the users time directive. If allowed enough time, the AFP will employ a major part of this time iin n “learning” the network. During the learning phase, the AFP tunes up its internal parameters. Towards the end of the user-defined time, the AFP switches to a randomised combinatorial search phase.
The role of this learning phase is extremely important in order to get good results. You should often let the AFP run over Remark: a night or a weekend by specifying corresponding target time. If you never run the AFP specifying a long time period, it will never be able to calibrate itself and will always perform from 10 to 70 solutions and stop. Network learning is performed by executing numerous fast and deterministic instances of the AFP. The one that obtains the best performance is memorized in the document and is, therefore, the most suitable for the specific network. The next time an AFP is executed it will start s tart where the learning process ended and it will use the parameter profile of the best solution stored in the document. Note: •
Th The e foll follow owin ing g sce scena nario rio will will dem demon onst strat rate e the u use sefu fuln lnes ess s of AFP AFP learn learnin ing g capab capabili iliti ties es:: - Create a GSM GPRS EGPRS project and import its network elements and maps. - Create a copy of “Atoll AFP module” and name it “Atoll AFP module 2”. - If the network has X transmitters, run “Atoll AFP module 2” for X / 10 minutes to obtain a cost Y. (Short execution) - Now run “Atoll AFP module 2” for a longer time (for example, X / 5 hours). - Another cost, Z, is obtained, which is better than Y (i.e. Z < Y). The network dependent information is memorized in the “Atoll AFP module 2” instance whereas the “Atoll AFP module” instance remains unchanged. - Now if you perform a short execution with “Atoll AFP module 2”, you can c an get the improved result (Z) right away. While a short execution of the “Atoll AFP module” instance will give the initial cost (Y). - If X / 5 hours is i s too long, you can perform the “learning” on a small ( representative) part of the network.
The Atoll AFP is built based on a specified s pecified COM interface designed as a part of Atoll’s open platform strategy. The interface is designed in such a way that puts aside elements that are not inherent to the AFP process. At the same time, through the modelling capabilities of the planning tool, the AFP can support complete list li st of features expected from an AFP.
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Basic AFP Tutorial Atoll AFP framework complies with its global open architecture strategy. An Any y AFP module, Atoll AFP or 3rd party AFP, can be interfaced and made available to RF planning engineers through Atoll. Furthermore, different AFP modules are activated, accept their main inputs and generate their main outputs in the same manner. This section teaches the basics of activating an AFP in Atoll.
2.1
AFP Process in Atoll The AFP process is a cycle in which the AFP is only one of its many steps:
Figure 2.1: AFP Proces Process s in Atoll The figure below gives a better view of interaction of the AFP with other elements in Atoll:
Figure 2.2: Interaction of the AFP with Other Elements Elements The following figure depicts the outputs of the AFP:
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Figure 2.3: AFP Out Outputs puts
2.2
Loading and Validating the Network To launch the AFP, choose the Automatic Allocation… command Allocation… command from the Frequency Plan menu Plan menu of the Transmitters folder context menu. This initiates a series of dialogs called the AFP wizard. wizard.
Figure 2.4: AFP Launc Launch h Wizard - AFP Session Tab
Figure 2.5: AFP Lau Launch nch Wizard - Separations Tab
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Specify the AFP mo module dule you would like tto o us use e and and set its parame parameters, ters, Choose Choose the n network etwork parameters parameters and and AFP perform performance ance in indicato dicators rs you want want th the e AFP to allocate, allocate, Specify Specify th the e net networ work’s k’s de defau fault lt sep separa aratio tion n requirem requirement ents, s, Consult Consult the ne network twork’s ’s “Except “Exceptional ional Pa Pairs” irs” and define define other other separatio separation n constraints constraints for for them, them, and Indicate Indicate whether whether interf interferenc erences es are to be included included in calculations calculations or not. not.
page 38 38.. The last wizard dialog For explanations of AFP performance indicators, refer to "AFP Performance Indicators" on Indicators" on page contains some global parameters that often vary from one AFP instance to another:
Figure 2.6: AFP La Launch unch Wizard - Global Parameters Tab The most important option here is the one proposing the two sources of the traffic load information. Traffic load can be read directly from the subcells table, which could have been filled manually, by the dimensioning process or by a KPI calculation. You can also specify that the traffic load should be read from the default traffic capture (explained later). Notes: •
In case case the the traffi traffic c lo load ad is ttake aken n from from the Subcell Subcells s tabl table, e, commit committed ted after after a KPI KPI c calcu alculat lation ion,, you must be aware of a certain difference: in the KPI calculation, Atoll divides the captured traffic by the timeslot capacity of the existing existing number number of TRXs, while the AFP requires it to be divided by the timeslot capacity of the required required number number of TRXs.
•
The traffi traffic c lo load ad is artif artificia icially lly increa increased sed to 0.1, 0.1, if it is is too too llow ow (les (less s th than an 0.1) 0.1),, in ord order er tto o maintain the AFP robust against partial data conditions. Hence, the AFP cannot completely ignore the existence of a frequency in a TRX.
Clicking Validate Validate will will start the data verification v erification and storage optimisation aimed at providing fast access to data needed by the AFP. This stage may generate many warnings for real-life networks (for example, values out of range). These are displayed in the Event viewer. It is recommended to revise the network data according to these messages and continue once all the data are clean and coherent. If a certain message is not cl clear ear or self evident, you can always contact Forsk’s technical support. The figure below depicts the Event viewer with some sample messages:
Figure 2.7: Event Viewer - Sample Me Messages ssages Let us look at two of these messages:
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Figure 2.8: M Message essage 1 This means that the value entered in the AFP weight column of the Transmitters table for the transmitter 19941 is invalid. In the database, this field’s name is “COST_FACTOR”. A value of –2 for the cost factor implies that the AFP should generate the worst assignment possible for the transmitter. It would be interesting to investigate the origin ori gin of this erroneous value as it may avoid possible errors in the future. Atoll automatically resets this value to 1 in order to avoid such calculation errors.
Figure 2.9: M Message essage 2 This message informs that 3678 subcells were loaded successfully. The next section explains the significance of the term ‘effectively selected’ and why 3678 subcells were loaded and only 6 selected for the AFP process.
2.3
Definition of the AFP Scope In the example above, the 6 subcells effectively selected for the AFP process had many potential interferers, neighbours, neighbours of neighbours, and/or transmitters with exceptional separation constraints with them. No AFP can perform a good allocation for these 6 subcells without “dragging in” a large part of the network. The AFP considers the part that is “dragged in” to be “frozen”. On the other hand, there are many other ways to freeze network elements in Atoll. Some precise definitions are provided in order to avoid misconceptions. Let us define 4 groups of transmitters (ALL, NET, SEL, RING): • • • •
ALL = A Allll the the transm transmitte itters rs in in the the pro project ject.. NET = Active transm transmitters itters that that pas pass s the filt filters ers on th the e main Tr Transmit ansmitters ters folder folder an and d on the main main Sites Sites folder. folder. SEL = Tran Transmitte smitters rs belonging belonging to th the e (sub)folder (sub)folder for for which th the e AFP was launched launched and and that are are located located insid inside e the focus zone. RING = Tran Transmitte smitters rs belonging belonging to NET, not b belong elonging ing to SEL and and having some some relations relationship hip with the the transmitte transmitters rs in SEL: If interferen interferences ces are to to be taken taken into ac account count (s (see ee the dialog dialog above), above), all all trans transmitter mitters s whose calculat calculation ion radii radii intersect the calculation radius of any transmitter in SEL will be included in RING. For large calculation radii (20 km for example), a single site can have a very large RING loaded. Nei Neighb ghbour ours sa are re always always includ included ed in RIN RING. G. If one transmit transmitter ter of an Exc Exception eptional al Pair is inclu included ded in SEL a and nd the other other is not, tthen hen the other other will will be includ included ed in RING as well. If BSIC assignme assignment nt is required, required, then then all the s second econd o order rder neighbou neighbours rs (neighbour (neighbours s of a neigh neighbour) bour) will will be included in RING as well.
Both the RING and the SEL parts of the network a re loaded. It is important to know which subcells are loaded as the cost is calculated for all loaded subcells. The RING part is frozen for all assignments (BSIC, HSN, MAL, MAIO and channels). The SEL part may be assigned some parameters but only the ones specified in the dialog above. For example, if the user did not select BSIC, it will not be assigned. In addition to the generic freezing options above, there are some finer freezing options available in the data structure: 1. 2.
Indivi Individua duall trans transmit mitter ters s ca can n be frozen frozen for cha channe nnell (a (and nd MAL) MAL),, HSN HSN and/o and/orr BSI BSIC C as assig signme nment. nt. Indi Individ vidua uall TR TRX’s X’s can can be be froz frozen en for for ch chan anne nell (and (and M MAL) AL) as assig signm nmen ent. t.
In an Atoll project, it is strongly recommended to avoid TRX’s without channels. For this reason, never create transmitters automatically if there are no channels to assign to them. Therefore, if the user does not ask for MAL/MAIO assignment, all SFH subcells are considered frozen and no TRX will be created for them. The same occurs when only a MAL/MAIO assignment is requested. In this case, all NH and BBH subcells will be considered frozen and no TRXs will be created. Note: •
22
See See De Deve velo lope perr Re Refe fere renc nce e Gu Guide ide fo forr deta details ils o on n the the TO TO_A _ASS SSIGN IGN and and FROZE FROZEN N assig assignm nmen entt states available in the AFP API.
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2.4
Preparing to Launch the AFP Once the network is loaded and all warnings resolved, the AFP launch dialog will appear. This dialog contains a short summary of the state of the loaded network, SEL + RING.
Figure 2.10: AFP Laun Launch ch Window Interference matrices can be managed through the Interference Matrices folder. You can have more than one interference matrices in your document. The top most active interference matrices set is used by the AFP. You can either embed the interference matrices in the document or store them in external files. fil es. Atoll compresses the interference matrices if stored in the .atl document itself. It is not necessary to load IMs or look for them each time AFP is launched. You can view the reports on different interference matrices available in i n the Interference Matrices folder. This report has a summary section which indicates the current state of the IMs.
Example 1: When 1: When partial IM info exists, we can see that 9 transmitters out of 24 do not have any interferers.
Figure 2.11: Partial Interfe Interference rence Matrices - Report
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Example 2: When 2: When complete IM info exists, observe that the IM topology is more or less normal.
Figure 2.12: Complete Interference Matrices - Report The AFP launch dialog also lets you define a generator initilialisation number. This number serves as a directive of randomness for the AFP process being launched. If the generator initialisation is set to 0, the AFP will be fully random. An integer other than 0 will define a given deterministic sequence for the AFP process. Each generator initialisation number (other than 0) corresponds to a deterministic sequence. Therefore, each AFP instance i nstance launched with the same generator initialisation number will yeild the same results. You can use this option if you want to have the same set of solutions every time you launch the AFP for the same part of the same network. The Atoll AFP has a single algorithm with a number of steps. The AFP ignores some of these steps if the alloted target calculation time is too short. One of these steps is deterministic, i.e. independent of the generator initialisation number, while the other steps are initialized by this number. •
Genera Generator tor Initi Initialisat alisation ion = 0 (defau (default lt value) sig signifies nifies th that at this inti intialisati alisation on number number will be calculated calculated randoml randomly. y.
•
Genera Generator tor IInitiali nitialisation sation 0 means means tthat hat the the number number will b be e the the one set by by the user. Every time you define define the same same number, the AFP algorithm will be initialised in the same way, and hence the set of solutions will be the same.
It is advised to set Generator Initialisation = 0, and let the AFP reach the end of the Target Computation Time defined. However, you must keep in mind that all the AFP computations c omputations are deterministic in the start, independent of the generator initialisation. The AFP must be allowed to compute during the target time to observe the effects of randomness. Notes:
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•
Since Since tthe he m met etho hod d chos chosen en b by y th the e AF AFP P de depe pend nds s on the the ttar arge gett time time p pro rovid vided ed,, yo you u mi migh ghtt not not get the same results using the same generator initialisation number if the defined target times are different. Therefore, to actually get t he exact same results from the AF P process, you must define a certain target time and a certain generator initialisation.
•
The AFP may be per perfec fectly tly det determ erminis inistic tic during during a port portion ion of the target target comput computati ation on tim time e (5 (5 15%). During this period, the randomness seed will have no effect on the solutions. If you want to see the effect of randomness, let the AFP calculate until the end of the target time, or set a shorter target time.
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2.5
Launching the AFP and Monitoring its Progress Provide a time quota and a generator initialisation number in the above dialog and launch the AFP by clicking Run. It is important to set a long time quota from time to time to allow the AFP to calibrate itself. If not stopped, the AFP will usually continue for a while before stopping by itself. Important: •
If onl only y a sho short rt time time is spec specifie ified, d, the full full op optim timisa isatio tion np pote otenti ntial al of of th the eA AFP FP will will not be utilise utilised. d.
The window below opens when the AFP is started, and displays information about the AFP process:
Figure 2.13: AFP Progre Progress ss Window The Progress section of this window in the top left displays the target time allocated to the AFP, the time elapsed and the number of AFP solutions that have been evaluated so far. The general information and interference matrices report section in the top right gives some general information about the current solution in real time. This display dis play depends on the selected AFP module. This section llists ists the status of the current solution, the initial cost, the cost of the current best solution, the cost of the previous solution and whether the previous solution was kept or rejected. You can use the >> button to switch to the report on the currently used interference matrices. The Event viewer has been made accessible through the AFP progress dialog in order to help the user keep track of all the important warnings and messages generated before and during the AFP process. This also enables you to export these messages as an AFP log file. If a solution is kept, a corresponding message appears in the Event viewer. Double-clicking the message in the Event viewer will open a dialog with the full details of this message, which will look something like the following figure.
Figure 2.14: Event Viewer Message - Solution Kept After the AFP is allowed to compute solutions and try to optimise the network for a while, the AFP progress dialog would look somewhat like this:
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Figure 2.15: AFP Progre Progress ss Window The Best Frequency Plan Costs section displays the current values val ues of modifiable and total costs, and their respective separation components. This section also displays the total weighted Erlangs of the network concerned in the AFP process, i.e. the total cost of a 100% interfered frequency plan). It gives a general idea of how good the cost of a certain frequency plan is. The cost of any solution remains between 0 and the Network Weighted Erlangs. The cost is as better as it is closer to 0. Apart from the above information, this section also contains a table listing the initial frequency plan and all the AFP solutions kept so far sorted in ascending order of cost. This table can display: • • • • • •
Modifia iab ble co costs Total costs Frozen costs Summ Summed ed comp compon onen entts Main com componen ponents ts (separation (separation vio violation lation co cost st compo component, nent, in interfer terference ence com componen ponentt and modified modified TRX co compone mponent) nt) Add Additio itional nal ta taxes xes (corru (corrupte pted, d, mis missin sing g or out o off dom domain ain TR TRXs) Xs)
For detailed description of modifiable and non-modifiable parts of the total cost, please r efer to "Modifiable and Non-Modifiable Costs" on Costs" on page page 51 51.. Using the buttons available in the Plan comparison section in the bottom right, it is possible to visually compare the initial frequency plan and the current best solution (with the Best Plan column in the AFP cost details table checked). Clicking these buttons opens dialogs containing graphs corresponding to ’Cost Distribution on Frequencies’ and ’Usage Distribution on Frequencies’. The cost of a frequency f is given as: C o s t f
=
FL i C o s t i
i TRXs u us sing f
Where, FL(i) is the fractional load of frequency f in the MAL of i, and cost(i) is the AFP cost of TRX i in Erlangs.
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Figure 2.16: Cost Distributions on Frequencies
Figure 2.17: Freque Frequency ncy Usage Distributions You can pause or stop the AFP process any time to check the current best solution, and resume optimising the network after you have checked it. Pausing the AFP process opens the AFP results window with the current best solution results listed.
2.6
AFP Outputs When calculations stop (completed or paused to view the curr ent situation), Atoll displays the frequency plan proposed by the AFP. All results/violations results/vi olations are listed in a dialog window. This window contains a table listing all the assi assigned gned resources. Transmitters located within the Focus zone are listed in the results dialogue. If a Focus zone is not available, the results are displayed for all the transmitters within the Computation zone. These resources and related items (transmitters, subcells) are coloured differently to indicate different reasons: • • • • • • •
Arc Arcti tic c blue blue:: froz frozen en res resou ource rce Red: resourc resource e modified modified compare compared d to the the prev previous ious allocatio allocation n but with with separati separation on viol violation ation Green: resour resource ce modified modified com compared pared to to the pr previous evious a allocat llocation ion respecting respecting the the separatio separation n constraints constraints Black Black:: re reso sour urce ce no nott mo modi difi fied ed Blue: Blue: re resou source rce a assig ssigned ned w with ith no no separa separatio tion n viol violatio ation n Purple: Purple: resou resource rce as assign signed ed bu butt with sepa separat ration ion viola violatio tion n Grey: items items an and d reso resources urces in involved volved in comp computatio utation n but not not available available for allocatio allocation n
Positioning the cursor over a resource in the table displays the reason for its colour in a tool tip. The AFP result dialog is a non-blocking dialog. It enables the user to access other Atoll windows while the AFP is still pending. Thus, it is possible to view vi ew other data or warning/error messages in the Event viewer (for example, the history his tory of AFP solutions). From this stage, it is possible to commit, to resume or to quit the AFP. It iis s good practice to keep a report through the export option before resuming the AFP. The user can also partially commit some of the results as explained in the next section. The results window displays all the results of the AFP session. It is possible to only display some of the results by checking/ un-checking the relevant choices in the Display options menu. You can choose to display the results related to: • • •
Cells (BSICs) Subcells (HSNs) TRXs TRXs (Cha (Channe nnels/M ls/MAL, AL, MA MAIO) IO) an and d rela related ted se separ parati ation on vio violat lation ions s
Selected AFP performance indicators (AFP TRX ranks, and total and separation costs at TRX, subcell, transmitter and site levels) will also be available in the results window. These AFP performance indicators are also available to export. You can choose whether to display the AFP indicators in the results as separate columns. The Show AFP Indicators command in the Display options menu controls the display of AFP TRX ranks, and total costs c osts and separation cost components at TRX, subcell, transmitter, and site levels.
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Figure 2.18: AFP Resu Results lts Window As the network had been loaded according to both the items to assign and the ones they relate to, it is possible to display the frequency plan of either: • •
Items belon belonging ging to th the e selected selected transm transmitters itters (see tthe he de definiti finition on of SEL), or Items b belong elonging ing to the loaded loaded tr transmi ansmitters tters (see (see the def definition inition o off SEL + RING). RING). In the precedin preceding g example, example, there there were no transmitters in the RING set, so the option is not available.
It is also possible to display detailed information about separation constraint violations, i.e. the co-channel and adjacent channel collision probabilities for relevant TRXs. TRXs . You can choose to display these separation constraint violations through the Display options menu. The Separation violations column lists each each type of separation constraint violation realted to a given TRX, i.e. exceptional pair, co-transmitter, co-site, or neighbour. Another column titled ’With the TRX’ contains a button for each type of separation constraint violation. This caption of this button shows the TRX with which the separation constraint violation occurs. Clicking this button takes you to the corresponding TRX row in the table. Right-clicking a row with a separation constraint violation opens a Separation Constraint Violations context menu, which opens a dialog mentioning the reason of violation when clicked. For example:
Figure 2.19: Separation Constraint Violation Details Message Use the Commit button to assign the allocated resources and AFP performance indicators. The resume button permits resuming the AFP optimisation from where it stopped the last time. Note: •
28
At tthe he bot botto tom m of th the e AFP AFP re resu sult lts s wi wind ndow ow,, me messa ssage ges s rela relate ted d to th the e la last st solu soluti tion on are are displayed, which may list problems as well.
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2.6.1
Partial Commit Functionality It is often required to commit only a part of the automatically generated frequency plan rather than committing it entirely. The purpose is to avoid committing TRXs that violate separation constraints (sometimes referred to as “not closing the frequency plan”). Future Atoll versions will incorporate advanced automatic filters for partial commit. The dialog examples below depict a case where removing a TRX eliminates a separation constraint violation on neighbours. Once a TRX is manually removed from the resulting plan, separation violations are recalculated (may take a few seconds). If the TCH TRX of transmitter Site36_3, S ite36_3, causing neighbour separation constraint violations, is removed from the sample frequency plan below, the resulting frequency plan has no neighbour separation constraint violations on the TCH TRX of transmitter Site36_1.
Figure 2.20: AFP Results Window - Partial Commit Feature It is possible to specify the action to be taken with each TRX individually, individuall y, or globally delete all TRXs with separation violations. It is also possible to mix the old plan and the new plan. Though this is not recommended, since it can cause interferences of which the user might be unaware. The dialog examples below depict how this operation can be carried out. The Delete the TRX option TRX option implies that the resulting frequency plan will wil l not respect the number of required TRXs. In the above example, note than the neighbour separation constraint violations at transmitter Site36_1 vanished once the TCH TRX at Site36_31 was deleted.
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Figure 2.21: AFP Results Window - Partial Commit Feature
2.6.2
Automatic Constraint Violation Resolution Different types of constraint violations, i.e. co-transmitter, co-site, neighbour, and exceptional pair, can automatically be eliminated from the propsed frequency plan using the Automatic Constraint Violation Resolution tool. This tool is accessible from the Actions button menu. The aim of this tool is to find the TRXs in the currently proposed frequency plan that cause constraint violations of any of the four following types: 1. 2. 3. 4.
Co-transmitter Co-site Neighbour Exceptional pair
Once it finds the TRXs that satisfy the criteria, it sets their corresponding values to Delete the TRX in the Channel Assignment column of the AFP results window. This tool lets you resolve any type of constraint violations v iolations for different types of TRXs, control or traffic. You can c an also define a threshold of co-channel and adjacent channel collision probabilities. This restriction will only set those TRXs to Delete the TRX, which have a co-channel or adjacent channel collision probability higher than the threshold you defined.
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Figure 2.22: Constraint Violation Resolution Tool
2.7
Visualising and Manipulating Results The Commit button copies the frequency plan to the data structure. It is not necessary to save the document or commit the changes to the database right away as the AFP cycle has not yet ended. At this stage, various generic and specific tools are available in Atoll, and can c an be used to inspect the candidate frequency plan. Interference and C/I prediction studies and various consistency checks are described in the following chapters of document. In addition to these, a useful tool is is also available in Atoll, called c alled the Search tool. Its function is to facilitate visualising co-channel and adjacent-channel transmitters. This tool is explained in detail in the User Manual. Other means of inspection include the common grouping, filtering, advanced filtering, display and tool tip management features.
2.8
Manual Frequency Allocation This section describes quick and useful techniques for performing manual frequency allocations in Atoll.
2.8.1
Manual Frequency Allocation for SFH Case It is possible to perform frequency allocations for irrgular pattern networks, i.e. patten allocation of type 1/N. The following set of operations will results in a frequency allocation even if the network is not a 100% regular pattern network. 1. 2. 3. 4. 5.
2.8.2
Run Run the the AFP so that that it cre creat ates es th the e rreq equi uire red d num numbe berr of of T TRX RXs. s. Grou Group p the ttran ransmi smitte tters rs by azimu azimuth th and and man manual ually ly assign assign the the MALs MALs to tthe he mo most st impor importan tantt azi azimut muth h gro groups ups.. Filter Filter ou outt these these azimu azimuth th gr group oups s and delet delete e the T TRXs RXs o off all ttran ransmi smitte tters rs that that were were no nott assign assigned ed a MA MAL L manual manually. ly. Run the A AFP FP ag again ain sele selecti cting ng M MAIO AIO assig assignme nment nt only. only. This This will will a assig ssign n proper proper MAIO MAIOs s to the the TRXs TRXs to w which hich MAL was manually assigned. Rem Remove ove the the filte filterr and free freeze ze the the existi existing ng TR TRXs. Xs. No Now w use tthe he AFP AFP to co compl mplete ete tthe he assign assignmen mentt (assig (assignin ning g all resources).
Manual Frequency Allocation for NH Case To carry out manual frequency assignment: 1. 2. 3. 4.
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Crea Create te a B Bes estt Se Serv rver er map and and d dis isp play lay iit, t, Disp Display lay n neig eighbo hbours urs of tthe he tran transmi smitte tterr fo forr which which you want want to fin find d a ffreq requen uency cy manu manuall ally, y, Open the Search tool, By sca scanni nning ng the the spe spectr ctrum um a g good ood freq frequen uency cy can easily easily be found found an and d can be be all alloca ocated ted tto o the transm transmitt itter. er.
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Figure 2.23: Scanning for Frequencies In this example, frequency 11 is not a good choice since it is used as a neighbour co channel. Frequencies 10 and 12 present similar characteristics.
Figure 2.24: Scanning for Frequencies On the other hand, frequency 14 is a good one and can be possibly allocated. None of the frequencies {13, 14, 15} are allocated at the selected transmitter of at its neighbours.
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Chapter 3 Frequency Planning Prerequisites
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3
Frequency Planning Prerequisites The principal difference between AFP and other planning activities is that the impacts of poor frequency planning are more widespread in a network. For example, poor planning of a site or a cell will have somewhat local influences, while implementing a poor frequency plan will affect a much larger part of the network. Moreover, creating a poor frequency plan is rather relatively easy, the presence of a single faulty parameter in the process can be sufficient for the damage the entire plan. Therefore, it is mandatory that the AFP user acquires a minimum level of knowledge regarding Atoll data model. This chapter familiarises the user with the essentials of the data model and depicts their relations with the AFP.
3.1
Atoll Data Model
3.1.1
Reliability and Propagation Often the user senses that the AFP does not have enough constraints: • •
The unfroze unfrozen n pa part rt of the A AFP FP cost is 0 a and nd th the e AFP stops due to to thi this s fact. fact. There appe appear ar to be close close frequen frequency cy reus reuses es in the rresultin esulting g frequency frequency plan.
This means that the problem is too “easy” for the AFP and the user would like to create a more difficult IM in order for the AFP to have a more difficult problem to solve. The best method to accomplish this is to increase the cell edge reliability and recalculate the IMs. When the reliability requirement is elevated, a larger part of the standard deviation is reduced from “C” when calculating the C/I for each IM entry. The user should also verify that the standard deviation is properly defined in all clutter classes and its default value. This verification is more important in the case of Atoll documents converted from older versions or connected to a database.
Figure 3.1: Model Standard Deviation - Default Value
3.1.2
HCS Layers HCS layers have several roles in Atoll. Their most important role is related to the way Atoll manages traffic maps. Different layers have different priorities and mobility limitations. li mitations. There is also the possibility to manage traffic overflow from one layer to another. The objective of all these options is to model the behaviour of a real network, where two potential servers that do not belong to the same layer usually do not compete for best server. When calculating an IM, or when generating an interference study, HCS layers are used in generating service zone maps, the basis of these calculations. If two transmitters belong to different layers, they can both serve the same pixel even if received signal from one is much stronger than the other’s. For equal HO margins, more HSC layers mean higher overlapping levels in the network. As the overlapping level increases, the constraint level in the IM and the amount of interference in an interference study also increase. Note: •
© Fo F orsk 2008
Be sur sure e to s stu tudy dy the the p pri rior orit ity y me mech chan anism ism in your your net netwo work, rk, b bot oth h in the the rere-se sele lect ctio ion n proc proces ess s and in the handover process. Define the corresponding HCS layers once you know its working. When using a traffic model, make sure that there are a few levels of mobility in order to model high speed / low speed mobility behaviours.
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3.1.3
Subcells Subcells are defined as a group of TRXs in the same transmitter. Two subcells of the same transmitter can request frequencies from different domains, require different C/I qualities, have different downlink power offsets and even have different Radio Resource Managements (RRM). Different RRMs can lead to different service zones under the same cell. Subcells are crucial for modelling concentric and dual band transmitters. In these cases, the TRXs belonging to the “inner” subcell serve traffic within a limited zone. Note: •
3.1.3.1
Key Roles of Subcells • • • • •
3.1.3.2
All All TRX TRXs s iin na s sub ubce cell ll shar share e tthe he sam same T TRX RX ty type pe..
Asso Associa ciating ting T TRX RX gro groups ups w with ith re requi quired red quali quality ty de defin finitio itions ns Associa Associating ting T TRX RX gro groups ups w with ith we weak ak / s strong trong constr constraints aints (interferen (interference ce , separation) separation) Asso Associa ciating ting T TRX RX gro groups ups w with ith d diffe ifferen rentt dom domain ain limit limitati ations ons Visua Visualis lisin ing g an and d fi filt lter erin ing g by TR TRX X Ty Type pe The ffollowin ollowing g additiona additionall para parameters meters are a also lso defined defined in the the Subcells Subcells table: table: HSN (since (since tthe he inn inner er zon zone e HSN may b be e diff different erent from the o outer uter zone H HSN) SN) Power offset Recept Reception ion thre thresho shold ld (ca (can n lim limit it the zone zone o off the inner inner subce subcell) ll) Hopping m mo ode Assignment Assignment mo mode de (in SFH SFH,, “grou “group p const constrained rained mode” limits limits th the e choice of of MAL to one one of th the e grou groups ps in the domain) Support of DTX Traffic Traffic load load and and sup supple plemen mentar tary y AFP AFP weig weight ht Some other other p parame arameters ters influen influencing cing th the e AFP in indirect directly ly (for example example,, the overflow overflow rate)
Concentric Cells and Dual-band Cells Concentric cells were created in order to exploit downlink power control (DLPC) and radio resource management (RRM) in frequency planning. This is accomplished by associating channels with subcells. Subcells may have different service zones with respect to the transmitter’s geographic coverage. For example, a subcell TCH_INNER covers a zone requiring minimum reception level of –75 dBm and TCH_OUTER covers a zone with minimum reception level of –94 dBm. In this case, the inner zone has a higher resistance to increasing i ncreasing interference. The AFP has the possibility ot assign a relatively interfered frequency to the TCH_INNER zone to give more choice to the outer zone. The other important property of concentric cells is the fact that a downlink power offset is associated with each subcell. The inner subcells can have higher DLPC implying that the frequencies assigned to the iinner nner zones will interfere less with other transmitters. Concentric cells permit a higher reuse pattern between inner zones, providing up to 40% increase in capacity. Atoll can fully exploit this increase in i n capacity since it calculates interferences between subcells. It uses the power offset and the C/I threshold that defines the subcell boundaries. Furthermore, it is i s also possible to define separation constraints at subcell level.
3.1.3.3
Minimum C/I The required quality thresholds for BCCH and TCH are usually 12 and 9 dB respectively. But, since the GSM standard tests this behaviour under the comfortable reception conditions of 20 dB above thermal noise, it does not reflect the behaviour for, for example, received signals being only 15 dB above thermal noise. Atoll provides the possibility to define these thresholds at subcell level allowing maximum flexibility and possibility to support a mixture of old and new equipment. Moreover, the safety margins corresponding to these values can be defined in the AFP cost definition. Refer to "Quality Target and C/I Weighting" on Weighting" on page page 53 53 for for more information.
3.1.3.3.1
Quality Targets Various quality targets can be set in Atoll by defining a C/I threshold value “min C/I”, with a probability threshold “% max interference”. These two values combined together define a quality target which implies that in order to have acceptable quality, the probability of having C/I lower than the “min C/I” value must be less than “% max interference”. This method enables Atoll to exploit the fact that a larger number of TCH channels can be assigned with quality requirements lower than the BCCH quality. This results in less constraining interferences and an easier and faster assignment. Weighting" on on page page 53 53 for for more information. Refer to "Quality Target and C/I Weighting"
3.1.3.4
Traffic Loads Traffic loads of all the subcells are used as input to the AFP. These traffic loads can be calculated by Atoll (default traffic capture) or imported from another source to the Subcells table. Atoll calculates the traffic loads as values from 0 to 1. However, the AFP can work with traffic load values from 0 to 1000. If the values imported to the Subcells table from any other source than Atoll are less than 0 or greater than 1000, the AFP returns an error message and stops. If the imported values are from 0 to 1000, they are converted to values from 0.1 to 1 using the following foll owing equation: V Ne w
36
=
1.8 2 0.1 + -------- tan 3 V Ol d + 2 V Ol d
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3.1.3.5
Local Domain Restrictions Low level domain restrictions can be introduced at subcell level through the excluded channels column in the Subcells table.
3.1.4
TRXs Atoll’s TRX table enables the following: • • • •
Support Support of an ex externa ternall ID space of the TR TRXs Xs of a tra transmit nsmitter ter (important (important for imp import ort and export export utilitie utilities). s). MAL MAL / ch chan anne nell a att TRX TRX leve level. l. MAIO a att T TR RX le level. Fine freezin freezing: g: Th The e user can freeze freeze specific specific TRXs in an unfrozen unfrozen transm transmitter. itter.
The TRX table does not contain an “active” field. Therefore, all TRXs in it should contain a valid frequency or MAL and are all considered to be on air. It is better to remove an entire TRX record than removing only the frequency or MAL from its channels list.
3.1.5
Freezing Flags A multilevel freezing mechanism enables freezing resources at TRX level as well as at transmitter level. This, in i n turn, enables the user to use an existing plan while assigning only newly added demand for channels. These options are in addition to the working zone limitations. Note: •
3.1.6
Wh When en free freezin zing g cha chann nnel els, s, ke keep ep in mi mind nd that that the the MAI MAIOs Os are are not not froz frozen en..
AFP Weights The AFP weight field in the Transmitters table enables the user to assign high or low weightings to certain transmitters. It can be used to improve quality at a problematic location or to boost quality in a particular covered region of the network. An additional AFP weight field exists at the subcell level. It enables the user to assign weighting to subcells. A conventional idea could be to assign a higher weight to the BCCH. The AFP uses the multiplicative product of transmitter level AFP weight and subcell level AFP weight.
3.1.7
Spectrum Administration Many levels of administration exist relative to frequency planning. In order to avoid confusion, here is a comprehensive list: •
ARFCNs ARFCN is the method employed by the GSM/DCS GSM/DCS standards to enumerate 200 kHz frequen frequency cy carriers.
•
Frequency Ba Ban nds Frequency Bands are subgroups of ARFCNs. Different equipment may be limited to different frequency bands (BTS, MS, …). In addition, propagation models use the central frequency of the band for calculating pr opagation.
•
Fr Freq eque uenc ncy y Dom Domain ains Domains are used for managing the usage of the Frequency Bands. For example, an operator may use frequencies 1 to 50 while the other uses 52 to 100. Splitting the band on channel usage basis is of great importance as well (BCCH frequencies, TCH frequencies, Hopping layer).
•
Domain Groups Domain groups are used for further managing the use of the frequencies in a domain. For example, f1 and f2 can be assigned at the same transmitter if and only if they belong to the same group. Another frequent use for groups is in the MAL assignment.
In Atoll, a domain is defined as a union of groups. It points to a frequency band and must be included therein. The AFP respects domain limitations at subcell level.
3.1.8
Redundancy and Subcell Audit Atoll incorporates some deliberate redundancies between the subcells and TRX levels, and the Transmitters table: • • •
The channel channel list in in the Tra Transmitt nsmitters ers table table is the intersect intersection ion of all ch channel annels s appearing appearing in the the TRXs of a transmi transmitter. tter. The hopping hopping mo mode de of a transmit transmitter ter is the hoppi hopping ng mode mode of it’s de default fault ttraffic raffic carrier carrier (t (the he TCH TR TRX X Type) The frequency frequency band band of the ttransm ransmitter itter (th (the e one use used d by the pro propagat pagation ion model model to deduce deduce the ce central ntral frequen frequency), cy), is read from the domain of the BCCH subcell of the transmitter.
Atoll considers the low level to be the accurate source of information. For example: example: • •
© Fo F orsk 2008
Atoll will automat automatically ically update update the T TRX RX table if the the chann channel el list of a transmitte transmitterr in the transmitte transmitterr table is chan changed. ged. The freq frequen uency cy band band of a transm transmitt itter er ca canno nnott be edite edited. d.
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AFP Reference Guide These redundancies provide some additional features (for example, grouping transmitters according to the frequency bands). On the other hand, there is a chance of mistakes and bugs which may damage a redundancy in the ATL file. Therefore, it is recommended that the audit tool be used from time to time in order to fix these problems (right click the Transmitters folder, choose Audit from the Subcells menu).
3.1.9
Neighbour Importance Neighbour importance field exists in the neighbour relation tables. It is also available in the AFP and can assist in resolving congestion situations. This is discussed in detail in subsequent chapters.
3.1.10 3.1.11
SeparationConstraints Table
It is a separation exceptional-pair table containing pairs of subcells with wi th associated separation requirements. Special separations have a higher priority with respect to all other separations and can be used to relax separation constraints as well.
SeparationRules Table and Rule Priority The SeparationRules table is simple to understand once the order of priority that exists between various separation rules is kept in mind: 1.
Highest priority: exceptional pairs
2.
Second higher: co-transmitter
3.
Third priority: co-site
4.
Last priority: Neighbour.
For example, if two subcells are neighbours and at the same site, si te, their associated separation requirement will be according to the co-site separation rules. And, if this separation requirement is not fulfilled, their separation violation costs will be weighted by the co-site weight. Separation rules depend on equipment, and refer to the non-hopping configuration. Separation rules are "administration rules" that are set once according to the equipment and are not meant to be modified during routine operations. Separation rules do not depend on whether SFH is available in the network or not. Atoll and the AFP consider SFH independent of the separation rules. If you relax the separation constraints, and have SFH TRXs, this means that you are asking the AFP and Atoll to take into account the effect of SFH twice.
3.1.12
Adjacency Suppression Adjacency suppression is defined as the difference between the required C/I and the required C/A (C/A being the “Carrier to Adjacent Intensity ratio”). By default this is set to 18 dB following the standard. It is available in the Predictions folder properties dialog window under the name “Adjacent channel protection level”. The GSM standard requires this desired behaviour but does not specify any amplification level. It is recommended to be sure that the physical equipment in the network support this value. The value of this parameter is used in the AFP when extracting the interference caused by an adjacent channel, and in Atoll in interference and C/I studies. It might be a good idea to use a safety margin for this parameter and set it to 16 dB, for example.
3.2
AFP Performance Indicators The AFP can be used to generate different AFP performance indicators and listing them in the AFP results window. These performance indicators describe the states of different network entities, such as TRXs, subcells, transmitters and sites.
3.2.1
AFP TRX Rank AFP TRX Rank provides a ranking of the TRXs in a subcell. If a TRX rank is high, it implies that the frequency (channel) corresponding to this TRX has bad usage conditions. TRX ranks indicate the best and worst quality TR Xs in each subcell, which maybe candidate GPRS TRXs or potentially removable TRXs to improve overall network quality. The OMC might use rank (or preference) information for better RRM. Notes: •
Rank = 1 is the best rank.
•
TRX TRX R Ran ank k iis s tthe he co corr rres espo pond ndin ing g ffie ield ld in th the eT TRX RX ta tabl ble. e.
As it is during an AFP process that frequencies and MALs/MAIOs for different TRXs of a subcell are chosen, the AFP tool stores and manipulates the information about TRXs in good and in bad conditions. If you choose AFP Rank indicator to be allocated when starting an AFP session, each cost improving solution will go through a TRX rank assignment. If no improving plan is found, TRX rank will be assigned for the initial plan (like BSIC). TRX ranking within a subcell is performed on the basis of TRX costs.
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Chapter 3: Frequency Planning Prerequisites In many cases of MAL/MAIO assignment, only one or two of a TRX’s MAIOs violate separation constraints. Therefore, a higher ranking will be assigned to the MAIO violating the separation constraints.
3.2.1.1
TRX Rank Usage This information can help increase performance in certain cases where a cell and its neighbour are not loaded with traffic at the same time (for example, a stadium and its parking lot). In such cases, it is possible to decrease call blocking by adding the TRXs in bad conditions to the concerned c oncerned cells. If the BTSs do n ot recognize TRXs in bad conditions, the overall network behaviour will either be very poor or difficult to predict even if the BTS knows how to track ranking in real time. TRX ranks may be required by the OMC in order to optimise the spectral efficiency. In some networks, a part of the decision-making process at the OMC may be transferred to the BTSs when this information is available. Even if such a “smart” system exists, it might be better to know the TRX r anks in advance to improve predictability and consistent behaviour. Apart from these uses, AFP TRX ranks can be used in post-AFP optimisation. For example, once you perform AFP, you can freeze all TRXs with ranks less than or equal to X. So that a new AFP instance will concentrate on a smaller subset of the most interfered TRXs in the most loaded subcells. A TRX will not be considered frozen for TRX Rank assignment if and only if it is selected for AFP allocation and has not been frozen at Transmitter level or by the AFP launch Wizard.
3.2.2
Total Cost and Separation Violation Cost Component Total cost and separation violation cost component at the TRX, subcell, transmitter and si site te levels can be computed and displayed as AFP performance indicators. These are the cumulated total costs and the cumulated separation violation costs of each TRX, subcell, transmitter and site. In order to be able to compute and display these results, you must add AFP_COST and AFP_SEP_COST fields (of type SINGLE) to the TRX, Subcells, Transmitters and Sites tables. AFP_COST field and AFP_SEP_COST field correspond to the total cost and separation cost component respectively. These AFP performance indicators are available in the list of AFP performance indicators to be computed available when launching launching the AFP tool. The AFP cost assignment to the TRXs, subcells, transmitters and sites is carried out at the same time as the TRX rank assignment. Once a frequency plan is committed, the next instance of the AFP can concentrate more on the problematic TRX/subcell/transmitter/site to improve results. Another use of this feature can be to automatically limit the modification scope to the problematic cells/sites. This feature can deliver a significant quality gain.
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4
Frequency Plan Optimisation
4.1
Step 1 (Optional): Traffic Model Usage It is not possible to solve a difficult optimisation problem without having a traffic model. Following are the 4 principal roles of a traffic model: 1. To reduce the required number of TRXs where they are least needed and spectrum not available. 2. To indicate the least loaded TRXs, since they are less important and interfere less with others TRXs. 3. To reduce the constraint level of the IM (for example where interferences are limited to low density surface). 4. To provide an accurate quality estimation of the resulting frequency plan. The first point is currently implemented through a dimensioning model, which is explained in this chapter. c hapter. Moreover, it will be available as an AFP option in one of the future versions (i.e. the AFP will optimise the decisions so as not to respect the required number of TRXs. In other words, it will perform a spectrum oriented dimensioning). The second role is carried out by the traffic loads. In order to understand traffic loads better, traffic capture is also described subsequently. The third point is explained alongwith the description of the IM and the last point is detailed in chapter 5. The Atoll traffic model is quite advanced. To gain familiarity with the concepts of user profiles, environments, services, mobile types, terminal types etc. a new user should refer to the Atoll User Manual. These traffic model entities can be used to benefit from all possible capacity gaps in a network. The simplest application here, would be to use a clutter weight oriented model. The more advanced models and techniques of creating traffic maps, based on traffic-by-transmitter etc., are also explained in detail in the Atoll User Manual. This chapter provides with the basic know-how on creating the simplest model using clutter information and clutter weights.
4.1.1
Creating a Traffic Map Based only on Clutter Weighting There are two simple methods: •
Usin ing g a ra ast ste er ma map -
•
Defin Define e a simple simple user profile profile ffor or an act active ive user with with voice service, service, speaking speaking 3600s 3600s per hour hour (i.e. consum consuming ing 1 Erlang). Creat Create e a traffic e environ nvironment ment of th this is kind of use userr profile wit with h a densit density y of 1 and pedestrian pedestrian mobility mobility.. Any mobility mobility can be used (e.g. 1), as it will be used for calculating IM where only the relative weight matters. Assign appro appropriate priate clutte clutterr we weightin ighting g to this traffic traffic environm environment. ent. In the Geo tab, tab, creat create e a new ttraffic raffic map ba based sed on e environ nvironments ments throug through h the GSM GSM GPRS EG EGPRS PRS Traffic Traffic folder context menu. On the drawing toolbar, select the traffic environment created earlier, click cl ick the polygon button and draw a polygon surrounding the computation zone. This raster map will appear in the Traffic folder.
Usin ing g a ve vect cto or ma map -
-
Defin Define e a simple simple user profile profile ffor or an act active ive user with with voice service, service, speaking speaking 3600s 3600s per hour hour (i.e. consum consuming ing 1 Erlang). In the Geo tab tab,, creat create e a new ttraffic raffic map map bas based ed on user user profiles profiles thr through ough tthe he GSM GP GPRS RS EGPRS Traffic Traffic folder folder context menu. Select the user profile just created with pedestrian mobility and assign density to the Density field. Assig Assign n app appro ropr pria iate te cl clut utte terr wei weigh ghtin ting. g.
-
Click the p polygon olygon b button utton a on ondensity the drawing dra too toolbar lbar and d draw raw a poly polygon gon surroundin surr ounding g the computat computation ion zone zone.. Double-click it and assign ofwing 1. This vector map will appear in the Traffic folder.
-
Both traffic maps are stored in the document and can be exported. An exported vector map is smaller than a raster one.
4.1.2
Performing a Traffic Capture Traffic capture is a means to cumulate one or more traffic maps, for voice and/or data services, for different terminals and provide a spreading of traffic per sector respecting layer l ayer priorities, frequency bands and other rules that c can an be defined by page 95 95.. Once the user. The details of this process are described in "Appendix 4: Traffic Capture and Dimensioning" on Dimensioning" on page traffic analysis is performed, a traffic capture object is available in the Explorer window Data tab. This traffic capture object contains traffic demand per [service, subcell] pair in terms of Erlangs for CS traffic and kbps for PS traffic. This traffic demand provides Atoll with an estimate of average demand in terms of # TSL used. The AFP combines this traffic capture with the number of required TRXs and their timeslot configurations to generate traffic loads (assuming the AFP will create the required number of TRXs indicated in the subcell table). The dimensioning process reads the basic information contained in the traffic capture to find out the number of TRXs needed to support a user defined blocking rate, HR ratio etc. See "Appendix 4: Traffic Capture and Dimensioning" Dimensioning" on on page page 95 95 for for details. The KPI calculations combine traffic capture with the current number of TRXs in the network and their timeslot configurations to generate current traffic loads.
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4.1.3
Keep Keep iin n mi mind nd tha thatt the the rreq equi uire red d numb number er of of TRXs TRXs iis s the the nu numb mber er of of TRXs TRXs rreq equi uire red d to carry carry a given traffic. This is the number of TRXs (usually) calculated through the dimensioning process. The number of existing TRXs is the current actual number to TRXs at a transmitter.
Creating IMs Based on Traffic IM calculation is either based on uniform distribution or on the maps used to perform the default traffic capture. In order to calculate IMs based on a traffic clutter weighting, •
Cre Create ate the traffi traffic cm map ap a as s descri described bed ear earlie lier, r,
• • •
Perf Perform orm a traffi traffic c cap captur ture e us using ing only only tthis his ttraf raffic fic map, map, Mak Make e this this tr traff affic ic ca captu pture re the the d defa efault ult one one,, and and Select th the e option ""Traffi Traffic c spreading spreading based based on the maps maps used in the defau default lt traffic traffic capture capture"" in the IM calculati calculation on dialog.
This option has the following advantages: •
Interf Interfere erence nce o over ver “hot “hot spo spots” ts” w will ill have have more more weigh weightt -
•
Example: Sites covering an important highway will interfere over the highway but the interfered surface will Example: Sites be less compared to the coverage. Therefore, not significant if no traffic is used.
Inter Interferenc ference e ov over er dead dead spots will not creat create e ov overhea erhead d co constrain nstraints ts -
Example: A Example: A large hilly park in the middle of a city is often not covered by a dedicated site since it has low traffic. The slopes of this hill are covered by many overlapping cells and tend to create many undesirable IM entries. If the weight of these slopes is reduced due to very little traffic, this can simplify an over-constrained problem.
See "Appendix 3: BSIC Allocation" Allocation" on on page page 94 94 to to understand further why traffic loads and interference information are not combined together in Atoll.
4.2
Step 2 (Optional): Neighbour Relations and Relative Weighting In many cases, neighbour relations are the most constraining elements for the AFP. Neighbour importance field of the neighbours table permits the AFP to partially ignore weak / far-away neighbours and concentrate more on the more important neighbours. This section details the use of this new feature in various scenarios.
Tip: Check neighbour allocation before running the AFP. Often a bad neighbour relation definition causes poor frequency plan performance.
4.2.1
Automatic Neighbour Allocation Neighbour importance has two major roles in Atoll: 1.
Weighting the neighbour relation in the AFP.
2.
Ranking the neighbours so that Atoll can select the n most important i mportant neighbours.
The configuration presented below is recommended in order to use the resulting neighbour importance in the AFP. • • •
Coverage Factor: Adjacency Factor: Co-site Factor:
1% to 81% 20% to 90% 70% to 100%
Notes: •
The The d def efau ault lt va valu lues es fo forr c com ompu puti ting ng impo import rtan ance ce va valu lues es ar are: e: - Coverage Factor: 1% to 30% - Adjacency Factor: 30% to 60% - Co-site Factor: 60% to 100%
•
The nei neighb ghbour our alloca allocatio tion n algo algorit rithm hm works works a as s in ear earlie lierr versio versions ns with with thes these e defa default ult val values ues.. Changing these values changes the priority definitions of the neighbour allocation algorithm. Refer to the Technical Reference Guide for more details.
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Figure 4.1: Autom Automatic atic Neighbour Allocation AFP can be launched once the results of the neighbou neighbourr allocation have been generated and committed. Note: •
4.2.2
In the resu results lts genera generated ted by Atoll Atoll a afte fterr neig neighbo hbour ur all alloca ocatio tion, n, the sum of import importanc ance e va value lues s of of all neighbour relationships of a sector is not 1.
Importing Neighbour Importance Various sources of neighbour importance exist: • • •
OMC HO HO s sttatist istics Test mobile mobile data data m measure easurement ments s (which ignor ignore e inte interferen rferences ces be between tween non-n non-neighb eighbours) ours) Other
As with any other source of information, it is the user’s task to prepare and import this external data. The units of the neighbour importance are probabilities and are expected to reamin between 0 and 1.
4.2.3
Extending Existing Neighbour Relations
Extending an existing neighbour relation should be performed often either to solve some HO problems or because of addition of new sites. Such operations usually imply that a fr esh frequency allocation be carried out. The AFP would be required to use the original neighbour relations as well as the new additional neighbours, yet in a different way (with a different weight). In addition, the AFP would require access to the former (complete or partial) source of neighbour importance as well as to the new values of neighbour importance calculated for the recently added relations. The neighbour importance of the original neighbour assignment is probably more reliable than the one calculated using path loss calculations. This section explains how this can be done: 1. Export the current neighbour relation into a file called AllCurrentNei.txt using the generic export feature available through the context menu of the table, 2. Export all the relations for AllCurrentNei_Importance.txt,
which
there
are
reliable
neighbour
importance
into
a
file
named
3. Import the file AllCurrentNei.txt into the neighbour exceptional pairs so that the existing neighbour allocation is forced (usual operation for extending an existing allocation), 4. Run automatic neighbour allocation in order to extend your neighbour relations and/or assign importance where it was not already assigned. To keep important values lower than X%, all Max% values in the importance part of the dialog should be kept less than X. For example, if X is 50%, the configuration shown below can be used,
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Figure 4.2: Automa Automatic tic Neighbour Allocation Results As can be observed in the figure above, all new neighbour neighbour relations have weak importance values. 5.
Commit the allocation,
6.
Import the file, and answer “no” if asked to remove neighbours of modified transmitters. The screenshot below shows that the neighbour relations now comprise old neighbours with a higher hi gher importance and new neighbours with a lower importance automatically calculated by Atoll.
Figure 4.3: Neighb Neighbours ours Table
4.2.4
Importing Partial Sources of Neighbour Importance Atoll’s generic import feature can be used to import the data easily. In order to import, the user should know the location to place this imported data (Importance column of the Neighbours table) and the data units (probabilities (probabiliti es between 0 and 1). If your network statistics do not provide you directly with the importance of neighbours, you can calculate neighbour importance from other statistics. Then, this calculated importance can be imported to Atoll and provided to the AFP as input. For example, if you have statistics about the number of handovers between two sectors, you can calculate the importance of the different neighbours of each cell from these statistics. Consider two sectors, A and B. Let X be the "Average Activity of a Relationship" in the network, i.e., the sum of all handovers of all the sectors divided by the number of neighbour rela-
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Chapter 4: Frequency Plan Optimisation tionships. If the number of handovers from sector B (neighbour of sector A) is Y, the importance of sector B for sector A can be given by:
I m p o r tan c e
=
1 If If Y X Y --- If Y X X
In this way, when a relationship has more than the average number of handovers, its importance will be the highest it can be in Atoll, i.e., 100%. Otherwise, the importance will be less than the average.
4.3
Step 3 (Optional): Using Dimensioning The Atoll dimensioning model, combined with the traffic capture, is a strong tool for frequency plan optimisation. In most cases, where a spectrum problem exists and the problem does not originate from the neighbour relation, the second most important task is to reduce the number of required TRXs in a selective and careful way. This optimisation can currently be carried out with the help of the dimensioning model. In future versions, it may be available directly through the AFP.
4.3.1
Optimal Dimensioning of an Existing Network 1. Run the AFP and commit the resulting frequency plan. Proceed to the next step if this frequency plan is not satisfactory and the TRX demands have to be reduced. 2. Increase the service blocking rates (from 2% to 4% for example). The screenshot below shows: -
Wh Wher ere e th this is ca can n be d don one e (S (Ser ervic vices es ttab able le). ). Tha Thatt the dim dimens ension ioning ing m mode odell is based based on bloc blocking king.. The ef effect fect this this chan change ge has o on n the re required quired number number of TRXs (t (the he num number ber of existing existing TRXs being being the previou previous s number of required TRXs for 2% blocking rate committed in Step 1).
Figure 4.4: Dimensio Dimensioning ning Process 3. Recalculate the traffic capture since service definitions have changed and then launch l aunch dimensioning. Some transmitters will have less required TRXs while others, which were more loaded, have the same number of required TRXs as before.
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AFP Reference Guide Running the AFP once more can return an improved frequency plan, as the following example shows:
Action performed
AFP cost for the empty network, indicating the number of weighted Erlangs
Sum of Number of Required TRXs
Original network
603.6
100
106
9.7
0
After increasing the Blocking Probability to 4% and dimensioning
601.4
95
96.6
9.4
0
Separation Interference Violation Cost Cost
Missing TRX Erlangs
The above experiment proves that the capacity difference between the two networks is very low (first column, around 2 Erlangs). This by means that the reduction of 5 TRXs leads a very minor decrease in capacity. This is due to the fact that this was done dimensioning considerations rather thantoother possible considerations. The AFP generates a better plan after this decrease in the number of TRXs. The AFP cost units are Erlangs, therefore, we can compare the 2 Erlangs lost because of capacity to the 10 Erlangs gained because of better AFP cost. Note: •
It is is po poss ssibl ible e to set set a ““Ma Maxim ximum um num numbe berr of TRXs” TRXs” in tthe he Tra Trans nsmi mitt tter ers s ta tabl ble. e. You You c can an cop copy y and paste the current demand to this column, thus forcing the dimensioning process to respect the current state of the network as an upper bound. This possibility is a handy in all possible cases of difficult frequency allocation.
4.4
Step 4: Optimal Usage of the Atoll AFP
4.4.1
Introduction to the AFP Cost Function
4.4.1.1
Combination of Separation Violation and Interference Probabilities The cost function of Atoll AFP has two main components. The first component is the cost for violations of separation constraints and the second component is the cost for creating interference. Atoll AFP gives each separation violation a cost equivalent to a certain amount of of interference, making it possible to sum both costs and minimize their sum. For example, the user can define that a separation violation violati on of 1 costs the same as x% of interfered traffic. This is weighted by the type of violation (co-transmitter separation violations vi olations have higher impact than neighbour separation violations). Through this equivalence, It is possible to sum separation violation and interference costs that share a common unit, i.e. percentage of interfered traffic. Following this principle, all other cost elements are also calculated in the same manner, the cost of Missing TRXs, the cost of corrupted TRXs, the cost of a TRX assigned out-of-domain frequencies and the cost of changing a TRX’s assignment.
4.4.1.2
Counting TRXs (Nodes) Instead of Relations (Edges) In the following example, each separation violation represents an edge and each TRX a node. All the 3 frequency plans proposed in this example do not respect all separation requirements for all TRXs, meaning that they all have bad nodes and bad edges. Now the question is that whether the AFP minimization target should try to minimize the number of bad edges or the number of bad nodes. Example: • •
Imagi Imagine ne a net network work wit with h 6 TRXs, al alll having a separa separation tion co constrai nstraint nt of 1 with with each o other ther (i. (i.e. e. 6 nod nodes, es, 15 Edges). Edges). The fo following llowing 3 cases demon demonstrate strate the wa way y the AF AFP P calcu calculates lates the the cost cost of an allocation. allocation.
Case 1
Case 2
Case 3
F1 is used 4 times, F2 and F3 are used one time each.
F1 is used 3 times, F2 twice, and F3 is only used one time.
F1, F2, and F3 are used two times each.
Number of separation violations is 6 (6 bad edges)
Number of separation violation is 4 (4 bad edges)
Number of separation violations is 3 (3 bad edges)
Tw Two o TRX TRXs s hav have e goo good d assi assign gnme ment nts s
On Only ly on one e TRX TRX has has a good good as assig signm nmen entt
No TRX has has a good good as assig signm nmen entt
The spectrum is not equally used
•
The spectrum is equally used
Atoll AFP prefers prefers C Case ase 1 by by default. default. Neverthe Nevertheless, less, it can be conf configure igured d to opt ffor or Ca Case se 3.
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The cost function has meaningful units, i.e. Interfered Erlangs.
b. The ability to focus problems on a TRX that is already 100% interfered and to improve the others instead of spreading interference on several TRXs. c.
The capability to respect a TRX based quality target, i.e. dismissing interference at a TRX that does n ot sum up to a certain considerable value (explained below).
The Node-oriented approach is an important feature of the Atoll AFP and provides a tighter correspondence c orrespondence between the AFP cost and the network quality.
4.4.1.3
Each TRX Cost The AFP cost function is summed up for each TRX according to the following logic: • • • • •
If TRX is corrupted, the tax of being corrupted is added to the cost, and multiplied by T( ). If TRX is missing (the required number of TRXs and the actual number of TRXs being different), the tax of missing TRX is added to the cost, and multiplied by T( ). If TRX has out-of-domain frequencies assigned to it, the tax of out-of-domain frequency assignment is added to the cost, and multiplied by T( ). Otherwise, Otherwise, the separat separation ion cost, the the inter interferen ference ce cost and the the changing changing load of this this TRX are summed summed up (probab (probabiilistically) and added to the cost, and multiplied by T( ). If this this sum is ve very ry sm small all,, it iis s disca discarde rded d (see (see "Quality Target" Target" on on page page 51 51))
Here, T() is an estimation of the traffic Erlangs using TRX
weighted by the AFP weight for this TRX.
The user can fully control the AFP cost target by determining the value of the cost function parameters. Some of these parameters belong to the data model, e.g. “Maximum MAL Length” and “Minimum C/I”, while others are present in the specifc AFP GUI. Appendix 2 explains how to find each of these parameters. Note: •
4.4.1.4
Th The e AFP AFP co cost st iis s th the e co cost st of of the the en enti tire re loa loade ded d ne netw twor ork, k, n not ot o onl nly y the the cost cost of of the the se sele lect cted ed or or non-frozen TRXs. In many cases, the AFP is authorized to change only a part of the network. Therefore, the part of the cost corresponding to the non-frozen part of the network and the part of the cost corresponding to the frozen part of the network are indicated.
Separation Violation Cost In this section, interference cost is ignored in order to understand the separation violation cost. A TRX having only one separation violation is considered. Let Sij denote the required separation between two transmitters. If f 1 is assigned at i and f 2 at j such that f 1 – f 2 S ij , this means that the separation constraint is not satisfied. Separation constraints can be violated strongly or weakly: •
For example, example, the p pair air of freq frequencie uencies s (1, 2) viola violates tes a separation separation requirem requirement ent of 3. The pair pair of freq frequencie uencies s 1 and 3 violate this requirement as well but is still a better solution than (1, 2) and, therefore, should have a lower cost.
Frequencies that are part of a MAL with a low fractional load and that disobey a separation constraint, should not be weighted the same as in non-hopping separation violation. In fact, the separation component is weighted by the burst collision probability, which is the multiplication of the victim’s fractional load and the interferer’s fracti fractional onal load.
Figure 4.5: Atoll AFP Module Properties - Separation Weights Tab
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AFP Reference Guide Example: Let Example: Let us consider the following simple case of a network comprising two TRXs in the same cell. The first, TRX i, has a MAL denoted as MALi. It is interfered by TRX k having MALk. TRXi and TRXk have a separation requirement of 2. Their MAL lengths are respectively 5 and 4. Unfortunately, one of their frequencies is the same (i.e. separation = 0), while all other frequencies are correct. For the case of a co-channel violation when the required separation is 2, the c cost ost of the separation violation is 90%, as shown in the dialog above. Since only one channel of each TRX causes interference, with length(MAL i)=5 and length(MAL k)=4, the collision probability is 1/20. Hence, the cost to consider is divided by 20, i.e. 90/20 = 4.5% for each TRX. In addition, since the two TRXs have different MAL lengths, they have different interferer i nterferer diversity gains: a gain of 1.4 for MAL length of 5 and a gain of 1.2 for MAL length of 4 (see "Appendix 2: Interferences" on Interferences" on page page 91 91 for for details). 1.4 10
Applying interference diversity diversity gain of 1.4 dB mea means ns that the cost will be divided by the value: 10
1.38 . For TRXi,
this will give 4.5% / 1.38 = 3.25%. For TRXk, the cost to consider will be
1 90 20 10 1.2 10
------ ------------------------
=
3.41% .
Now, in order to get the exact contribution to the separation cost component, these values are multipilies by the traffic load (Erlangs / timeslot) and by the number of traffic carrier timeslots in each TRX. Assuming the traffic load to be 1 and that each TRX has 8 traffic carrier timeslots, we will get (8 x 3.25 + 8 x 3.41), i.e. about 0.5 Erlangs for the two T RXs together. Note: •
4.4.1.5
In tthi his s ex exam ampl ple, e, tthe he A AFP FP w wei eigh ghtt wa was s as assu sume med d to be be 1, the the ttra raff ffic ic lo load ads s were were ass assum umed ed to to be 1, no DTX was involved, no other interference or violation was combined with the above, the global separation cost was set to be 1, and the co-transmitter separation weight was set to 1 as well.
Interference Cost Traffic on a TRX will be interfered if and only if co/adjacent-channel reuse exists within interfering transmitters. Each such reuse will reduce the amount of good traffic and incr ease the interference cost. It will be weighted by the global gl obal interference weighting factor, and will take into account the burst collision probability in the same way as in the example above. For more information, see "Interference Cost Component" Component" on on page page 88 88..
4.4.1.6
Probabilistic Cost Combination Assume that TRX is subject to a separation violation vi olation causing a cost of 30% of T( ) (T() = Traffic of TRX ) and in addition, a co/adjacent-channel reuse causing this TRX to be 40% interfered. This section explains how these two events are summed together. The solution to this problem is provided by a probabilistic approach: all different costs are considered as bad events and are combined as if these events were independent. The probabilities of events in this example are p(Violation) = 0.3 and p(Interference) = 0.4. The cost of the two together is given by: 1 – 1 – p V i o l a t i o n 1 – p I n t e r f e r e n c e
=
0.58 or 58%
Let P1, P2, ….Pn be the violation probability costs of the given TRX (one for each of its n violations). Let Pn+1, Pn+2, ….Pm be the interference probability costs of the given TRX (one for each of its (m-n) interferences). Let Pm+1 be the “changing TRX cost” described below.
The separation cost of this TRX will therefore be: 1 – i
n
1 – P i 1
m The additional cost of this TRX will be 1 – i
+
1
=
1 – P i – 1 – i 1
n
1 – P i 1
=
=
The interference cost uses the “min C/I” value, defined at subcell level, for which it may have precise pair-wise interference information. It may apply various gains to this C/I quality target due to frequency hopping and/or DTX.
4.4.1.7
Missing TRX Cost It is easy to have a 0-cost solution if the required number of TRXs criterion is not fulfilled (by removing all TRXs, for example). This is the main purpose of missing TRX cost. By default, the exact traffic that a missing TRX was supposed to carry will be counted by the cost function. However, the user can increase this tax (to 200% for example) if needed. In certain cases, creating more TRXs will not only generate interferences for the newly assigned TRXs but also for other TRXs that, otherwise, would have correct assignments. This parameter enables the user to tune the AFP in its tradeoffs between respecting the number of required TRXs and optimising quality.
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4.4.1.8
Th The e Atol Atolll AF AFP P al alwa ways ys a assi ssign gns s as ma many ny TRX TRXs s as tthe he “Re “Requ quir ired ed TRX TRXs” s” ffie ield ld ind indica icate tes. s. T The he user can only decide regarding the better plan, i.e. the previous plan having a better quality but some missing TRXs or the new plan having lower quality but having all required TRXs assigned. In future versions, the AFP will be capable of optimising these decisions as well.
Corrupted TRX Cost It is easy to generate a 0-cost solution if frequency domain constraints are not satisfied (by putting an arbitrary channel, for example). This cost component exists in order to avoid this behaviour. By default, 1000% of the traffic that a c corrupted orrupted TRX is supposed to carry will be considered impaired. In some cases, fixing the assignment on a group of corrupted TRXs will not only result in an interfered assignment for these TRXs but also for many other TRXs that, otherwise, would have correct assignments. It is for this reason that this tax is higher than 100%. Note: •
A TRX TRX is c corr orrupt upted ed not onl only y ifif itit c cont ontain ains s freq frequen uencie cies s that that are out of dom domain ain but also also when when:: - An NH TRX has a MAL with more than one frequency - A TRX has no channel at all - A group constrained SFH TRX is assigned a MAL that is not strictly a group of its domain - An SFH TRX has no MAIO, or no HSN, or has an out of domain HSN / MAIO value.
In future versions, different corruption reasons will have different tax levels and the assignment of a corrupted TRX will not always be ignored.
4.4.1.9
Out-of-domain Frequency Assignment Cost TRXs may have proper ARFCN assigned yet may not comply with the frequency domain definition. In many cases, the frequency domain limitations are not fully respected in the surroundings of the zone considered for frequency planning. This cost component can not be ignored or be modelled by the corrupted TRX cost because such a corrupted TRX can interfere and be interfered, which will be ignored in both the cases. If a TRX is assigned out-of-domain frequencies (channels) but has correct ARFCNs, it will have dual influence on the cost: 1. The normal cost of interference, separation and/or modification. 2. An additional cost of having out-of-domain channels, multiplied multipli ed by the number of frequencies out of domain and divided by the MAL length. Note: •
4.4.1.10
If SFH SFH and and group group co cons nstr trai aine ned d su subc bcel ells ls have have out out-o -off-do doma main in ch chan anne nels, ls, and and are are fr froz ozen en,, th the e frozen TRX will be ignored altogether.
Quality Target It is often required to handle small and large amounts of interference in different manners. For example, an operator might prefer to have 10 transmitters with 2% interfered traffic in each, rather than to have 2 transmitters with 10% interfered traffic in each. The Global Cost section of the Atoll AFP properties dialog window’s Cost tab provides an option to dismiss interference and separation costs that do not sum s um up to the value of the parameter "% Max Interference" defined in the Subcells table for each subcell. TRXs having less l ess percentage of interference than that defined in the "% Max Interference" are considered to have 0 interference and are excluded from the cost. This feature can be used to distribute the interferences equally among some transmitters in stead of having a few with very v ery low interferences and others with high interferences.
4.4.1.11
Modifiable an and N No on-Modifiable Co Costs Interfered Erlangs or separation constraint violations between frozen TRXs can not be resolved by the AFP. The AFP can only reduce the non-frozen cost, which is the modifiable cost. Modifiable and non-modifiable parts of the total netwok cost are linked li nked in concept with the definition of the AFP A FP scope. See "Definition of the AFP Scope" Scope" on on page page 22 22 for for more information. Four groups of transmitters can be defined with respect to AFP: • • • •
ALL = A Allll the the transm transmitt itters ers in the pro projec ject. t. NET = Active transm transmitter itters s that pa pass ss the fil filters ters on tthe he main Transm Transmitters itters ffolder older an and d on the main main Sites Sites folder. folder. SEL = Transmitte Transmitters rs belon belonging ging to the the (sub)folde (sub)folderr for which which the AFP wa was s launch launched ed and that that are lo located cated in inside side the focus zone. RING = Transmitt Transmitters ers belonging belonging to to NET, not belong belonging ing to SEL and and having having some relatio relationship nship with with the tra transmitt nsmitters ers in SEL: If inter interferen ferences ces are to be taken taken into ac account count,, all transmitters transmitters wh whose ose calculation calculation radii radii intersect intersect the calculat calculation ion radius of any transmitter in SEL will be included in RING. For large calculation radii (20 km for example), a single site can have a very large RING loaded.
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Nei Neighb ghbour ours sa are re always always includ included ed in RIN RING. G. If one transmit transmitter ter of an Exc Exception eptional al Pair is inclu included ded in SEL a and nd the other other is not, tthen hen the other other will will be includ included ed in RING. If BSIC assignm assignment ent is required, required, tthen hen all the the second order order neighbo neighbours urs (neighbou (neighbours rs of neig neighbou hbours) rs) will be included in RING.
The total cost of the network corresponds to SEL+RING. It contains the modifiable as well as t he non-modifiable parts of the network costs. The modifiable part of the total cost of the network corresponds to SEL. However, this cost does not include costs corresponding to frozen entities of transmitters in SEL. The non-modifiable part of the total cost of the network corresponds to RING. It includes the costs corresponding to frozen entities of transmitters in SEL. In each instance of an AFP process, there might be entities frozen by the user. In addition to the generic freezing options, there are finer freezing options available in the data structure:
4.4.2
1.
Individual transmitters can be frozen for channel (and MAL), HSN and/or BSIC assignment.
2.
Individual TRX’s can be frozen for channel (and MAL) assignment.
Most Important Cost Function Parameters and Tuning It is strongly advised that the user should fully understand the different cost function parameters before manipulating them. In order to understand the parameters that are not explained in this section, please refer to "Appendix 1: Description of the AFP Cost Function" on Function" on page page 85 85 and and "Appendix 3: BSIC Allocation" Allocation" on on page page 94 94.. The figure below depicts the Cost tab of the AFP properties dialog:
Figure 4.6: Atoll AFP M Module odule Properties - Cost Tab
4.4.2.1
Interference Weight vs. Separation Weight The most important parameters are the ones outlined by rectangles in the figure above. Interference and separation weights are used as multiplicative factors before each interference or violation event. Therefore, these parameters have the ability to reduce one type of event cost compared to the other. If these two parameters are set to low values (for example, 0.1 and 0.035 respectively), AFP will be forced to work according to the edge-oriented strategy, which is probably not the recommended approach. By default, interference events are less important than separation violation events.
4.4.2.2
Cost of Changing a TRX The second most important parameter (also outlined with a rectangle in the figure above), is the cost of modifying a TRX. This is recommended to be used if the non-frozen part of the network should be changed as llittle ittle as possible. The following experiment shows the effects using this parameter can have:
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Test case: A network with 90 transmitters in total, 15 frozen transmitters and sum of required TRXs = 257. Only 193 good TRXs were already allocated. 64 TRXs should be created / newly allocated with as little influence as possible on the other 193 TRXs. For a cost of changing a TRX = 1
AFP changed only 98 TRXS
For a cost of changing a TRX = 0.3
AFP changed only 129 TRXS
For a cost of changing a TRX = 0.1
AFP changed only 139 TRXS
For a cost of changing a TRX = 0
AFP changed 162 TRXS
4.4.2.3
Quality Target and C/I Weighting
4.4.2.3.1
Quality Target The Global Cost section (outlined with a rectangle in the figure above) lets you define the quality target mechanism for the AFP cost. 1. If you select "Do not include the cost of TRXs having reached their quality targets (% Max Interference)", Atoll will not take into account the cost of those TRXs which have less % of interference than that defined in their corresponding "% Max Interference" in the Subcells table. The total cost will only include i nclude the costs of TRXs whose interference is still higher than this threshold value. 2. If you select "Take into account the cost of all TRXs", Atoll will consider the cost of all the TRXs ignoring whether they have reached their quality targets, defined in the "% Max Interference" in the Subcells table, or not. For example, consider a frequency plan with only one interfered TRX with 10% interfered traffic, and another frequency plan with 10 interfered TRXs with 1.5% interfered traffic in each. Assume that you have set the "% Max Interference" for all the TRXs in both the cases to 2%. If you choose the 1st option in the AFP global cost settings, Atoll will prefer the solution with 10 interfered TRXs with 1.5% interfered traffic rather than having 1 interfered TRX with 10% interfered traffic.
4.4.2.3.2
C/I Weighting When the C/I weighting option (the bottom rectangle), related to the quality threshold, is used, the AFP takes into account that the traffic having close-to-threshold C/I conditions is neither 100% satisfactory nor 100% corrupted.
Figure 4.7: C/I Weigh Weighting ting In this way, safety margins on the threshold C/I conditions can be avoided. Therefore, the user must specify a margin around which a “slope” is created, as illustrated in the figure above. This figure corresponds to an interference relation between two TRXs. It describes the distribution distri bution of traffic according to C/I conditions. c onditions. It depicts the effect of 3 different quality requirements on the interference cost of a co-channel frequency reuse. It can be observed that, when a low quality (C/I > 8 dB) is required, less traffic is considered as interfered than for a high quality (C/I > 11 dB). The option ‘C/I >10 dB + 2dB margin’ has the advantage of not being too strict on one hand, and yet trying to achieve high quality if possible. It is visible from the above figure how it integrates the different traffic classes into the interference cost.
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4.4.2.4
Separation Weights Settings The Separation Weights tab enables the user to define relative weights of different di fferent separation types with respect to each other and of one co-channel violation with respect to an adjacent channel violation and so on. The figure below shows the Separation Weights tab of the AFP properties dialog.
Figure 4.8: Atoll AFP Module Properties - Separation Weights Tab Other tabs of the AFP module properties dialog are more advanced. Please refer to the Atoll User Manual for more information on AFP module properties tabs.
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5
Means to Evaluate Frequency Plans
5.1
Estimating Frequency Plan Quality
5.1.1
Using Interference Studies The full description of the interference study features is outside the scope of this document. Nonetheless, it is important to understand that a geographically based interference study has an important advantage over any simulation based on pair-wise interference matrices (or histograms). Atoll interference studies are geographic studies that analyse each point on the map. For each point, an interference study estimates the carrier power and then sums up the interference powers taking burst collision probabilities, DTX, and traffic load into account. As the AFP works with interference matrices, it is limited to c coarse oarse estimations of interference combination and los loses es knowledge of the geographical location of interference events. It is due to this reason that the interference study output is much more accurate than the AFP cost.
Figure 5.1: Inte Interference rference Study Report The column “Erlangs (based on traffic load)” is available in the interference study report as seen above. This column uses a traffic model similar to the one used by the AFP: • •
It spreads spreads the ttraffic raffic o off each su subcell bcell (# (#TRX TRX x traffic traffic load x # timeslots) timeslots) on the service z zone one of the the subc subcell. ell. Then, it sums sums up the the interfer interfered ed tr traffic affic (in Erl Erlangs) angs) of ea each ch int interfere erfered d TRX.
This means that it is a TRX based estimation of interference and is much more accurate than any other tool available in Atoll. In order to be able to use this opt option, ion, you must check the “Detailed results” option when specifying specifying conditions for an interference study.
5.1.1.1
Various Interference Studies Following are the main differences between a TRX based interference study and a transmitter level worst case interference study.
5.1.1.1.1
TRX Based Interference Study If there are more than one TRXs per cell, a “TRX based” frequency plan analysis is usually usuall y required. This can be performed in Atoll using the “Detailed results” option of an “Interfered zones” study. The following figures depict this function:
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Figure 5.2: TRX Based Interference Studies For each TRX, Atoll retains a map of all the pixels that do not comply with the quality threshold (one map for each TRX). The threshold can be global or dedicated to each subcell (from the Subcells table). The maps can be visualised by the user and contribute to the overall statistics. statistics . The column mentioned earlier weighs the “bad” surface of each TRX map by the traffic carried by the TRX as seen by the AFP. Therefore, it is the most appropriate tool for frequency plan interference evaluation.
5.1.1.1.2
Worst Case Interference Study A Worst Case Interference Interference study allows generating the Wo Worst rst C/I (I being the worst interferer) per pixel or per serving transmitter at pixel. Statistics on these maps are available avail able with or without traffic weighting. The principal drawback is that pixels are coloured in both cases: when 1 out of n TRXs is interfered and when n out of n TRXs are interfered. Moreover, there is no information about TRXs (channels or frequency) responsible of these worst C/I values.
5.1.1.2
Visualising TRX Ranks with a TRX Based Interference Study You can also visualise and compare the AFP TRX ranks with the results of a detailed interference study. In the iinterference nterference study report table, as shown in the earlier earli er figure, the “Erlangs (based on traffic load)” column should rank the TRXs in i n the same order as the AFP TRX ranks. Make sure that the AFP cost is based on interferences and not separation constraints. In case of large networks, where it might be easier to compare these results using MS-Excel, you might not get a 100% match between these results and small variations in the order may exist.
5.1.1.3
Visualising C/I Distributions with a TRX Based Interference Study The figure above and the example below show how to get very detailed information about the various C/I conditions at TRX level. The different information seen in this screen-shot is part of the report obtained by creating several instances of an interfered zone study. The interfered zone study whose properties dialog is shown, is the closest to the default configuration. Its interference definition references the subcell quality threshold. In the two other interfered zones studies, the global threshold for the minimum and maximum TRX C/I to be included in each TRX’s map were fixed at the reference values. These studies show that there are more “weak interferences” (11.3 Erlangs) than “strong interferences” (6.3 Erlangs). The “weak interferences” being 8 < C/I
