UMTS Applied Radio Planning

April 20, 2018 | Author: Irwan Wahyudi | Category: 3 G, Gsm, Code Division Multiple Access, Decibel, Electronic Engineering
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UMTS Applied Radio Planning P025

Course Objectives ▪

Understand the key planning parameters of the UTRAN



Produce UMTS Link Budgets for various services



Understand UMTS Coverage and its KPI’s



Understand Capacity dimensioning in UMTS



Appreciate the Coverage/Capacity relationship in UMTS



Evaluate GSM-UMTS Co-location issues

1- Th The e UMTS UMTS Air In Inter terfac face e

The UMTS Air Interface 

UMTS ▪

Universal Mobile Telecommunication System



Also called “3G”, along with other IMT-2000 technologies



The evolution from GSM-GPRS-EDGE



WCDMA technology, part of the CDMA family

1- Th The e UMTS UMTS Air In Inter terfac face e

The UMTS Air Interface 

UMTS ▪

Universal Mobile Telecommunication System



Also called “3G”, along with other IMT-2000 technologies



The evolution from GSM-GPRS-EDGE



WCDMA technology, part of the CDMA family

The UMTS Air Interface 

1.1- WCDM WCDMA, A, Processi Processing ng Gain Gain and and Codes Codes

The UMTS Air Interface 

CDMA - Direc Directt Sequenc Sequence e Spread Spread Spectr Spectrum um

Frame Period (we may still need frames/timeslots frames/timeslots for signaling)

The UMTS Air Interface 

CDMA Spreading •Essentially Spreading involves changing the symbol rate on the air interface

Spreading 

Despreading 

P

P

Channel

f

f

P Tx Bit Stream

P

f f

Code Chip Stream

Air Interface Chip Stream

Identical codes

Rx Bit Stream

P f

Code Chip Stream

The UMTS Air Interface 

Spreading and Despreading 1

Tx Bit Stream

Spreading 

X

Code Chip Stream Air Interface Chip Stream

Despreading 

X

Code Chip Stream Rx Bit Stream

-1

The UMTS Air Interface 

Spreading and Despreading with code Y

Tx Bit Stream

-1

X

Spreading 

1

Code Chip Stream Air Interface Chip Stream

Despreading 

X

Code Chip Stream Y Rx Bit Stream

The UMTS Air Interface 

Interference mitigation Tx Signal

Rx Signal (= Tx Signal + Noise) P

P

f

f

P

P

Channel

f

f

Signal

Spreading Code

Spreading Code

P

Signal

f

Wideband Noise/Interference ▪

The gain due to Despreading of the signal over wideband noise is the Processing Gain

The UMTS Air Interface 

Processing Gain ▪

If the Bit Rate is Rb, the Chip Rate is Rc, the energy per bit Eb and the energy per chip Ec then

 E b =  E c ×

 Rc  Rb G p =

 Rc  Rb



We say the Processing Gain Gp is equal to:



Commonly the processing gain is referred to as the Spreading Factor

The UMTS Air Interface 

Visualising the Processing Gain W/Hz

W/Hz

Before  Spreading 

W/Hz Ec

After  Spreading 

Io

With Noise 

f

f W/Hz

W/Hz After  Despreading   /Correlation 

Post  Filtering  Orthog = 0 

f

Eb

dBW/Hz Eb

No

f

Eb /No No

f

f

Signal Intra-cell Noise Inter-cell Noise

W/Hz Post  Filtering  Orthog > 0 

dBW/Hz

Eb

Eb

Eb /No No

No f

f

The UMTS Air Interface 

Types of Codes ▪

Channelisation Codes Are used to separate channels from a single cell or terminal ▪



S2 C1 C2 C3

Scrambling Codes Are used to separate cells and terminals from each other rather than purely channels ▪



S1 C1 C2 C3

Different base stations will use the same spreading codes with separation being provided by the use of different scrambling codes.

S3 C1 C2 C3

The UMTS Air Interface 

Channelisation Codes ▪

Channelisation codes are orthogonal and hence provide channel separation



Number of codes available is dependant on length of code



Channelisation codes are used to spread the signal

The UMTS Air Interface 

Channelisation Code Generation ▪



Channelisation codes can be generated from a Hadamard matrix  x  x A Hadamard matrix is:





   x −  x   

Where x is a Hadamard matrix of the previous level

For example 4 chip codes are: ▫

1,1,1,1



1,-1,1,-1



1,1,-1,-1



1,-1,-1,1

Note: Note: These two codes correlate if they are time shifted

The UMTS Air Interface 

OVSF codes ▪

Orthogonal Variable Spreading Factor Codes can be defined by a code tree: Cch,4,0 =(1,1,1,1) Cch,2,0 = (1,1) Cch,4,1 = (1,1,-1,-1) Cch,1,0 = (1) Cch,4,2 = (1,-1,1,-1) Cch,2,1 = (1,-1) Cch,4,3 = (1,-1,-1,1) SF = 1

SF = 2

SF = 4

SF = Spreading Factor of code (maximum 512 for UMTS)

The UMTS Air Interface 

Code Usage Efficiency Any codes further down the trunk of a branch in use cannot be used





Any codes further out from the branch in use cannot be reused





C ch,4,0 =(1,1,1,1) C ch,2,0 = (1,1)

IN USE

By filling up branches of the code tree before starting new branches a greater capacity can be achieved Multiple code trees can be used from a cell but at an increased level of interference between channels C =(1,1,1,1) C ch,2,0 = (1,1)

C ch,4,1 = (1,1,-1,-1)

IN USE

C ch,4,1 = (1,1,-1,-1)

C ch,1,0 = (1) C ch,4,2 = (1,-1,1,-1)

C ch,1,0 = (1)

C ch,4,2 = (1,-1,1,-1)

C ch,2,1 = (1,C ch,2,1 = (1,-

C ch,4,3 = (1,-1,-1,1)

IN USE

SF = 1

IN USE

ch,4,0

SF = 2

C ch,4,3 = (1,-1,-1,1)

SF = 4 SF = 1

SF = 2

SF = 4

The UMTS Air Interface 

Scrambling Codes ▪







The spread data symbols are then scrambled by multiplying with a complex scrambling sequence Scrambling codes do not affect the chip rate The scrambling code is specific for a cell and thus serves to provide isolation between signals from adjacent cells There are 512 Scrambling Codes in the DL which can be allocated by Radio Planners

The UMTS Air Interface 

1.2- Ec/I Ec/Io, o, Eb/No Eb/No,, NR and Load Loading ing

The UMTS Air Interface 

Interference and Noise Densities ▪

From the point point of view view of a UE, every every other other UE’s power appears as Interference



Io is the Interference Density



No is the Interference + Noise Density





In general, when you talk about chips, or “Ec”, you use Io. When you talk about bits, or “Eb”, you use No. “No” consi considers ders Thermal Thermal Noise Noise at the NodeB NodeB

The UMTS Air Interface 

Ec/Io ▪



Ec/Io is the Chip Energy we obtain in the presence of the Interference generated by all other users Ec/Io of the Pilot Channel is used to: ▫

Estimate (“sound”) the channel (multipath characteristics)



Decide which server is “best server”



Make handover decisions



Typical requirement -15 dB

The UMTS Air Interface 

Eb/No ▪



Eb/No is the Bit Energy we obtain after despreading in the presence of the Noise generated by all other users and the Noise from NodeB equipment There’s a different Eb/No requirement for UL and DL: ▫



Typical requirement 1 to 10 dB Requirement varies by Bearer, Service, Multipath Profile, Mobile Speed, and Type of Receiver.

The UMTS Air Interface 

Noise Rise ▪



The effective noise floor of the receiver increases as the number of active mobile terminals increases. This rise in the noise level appears in the link budget and limits maximum path loss and coverage range. Three Users

Two Users One User Background Noise

The UMTS Air Interface 

Effect of Neighbouring Cells

Users in other cells cause interference. Typical ratio of power from other cells to power from own cell, i, is 0.6 (Urban Macrocells)

The UMTS Air Interface 

The Noise Rise Equation  I total P N 

1

=

 j = M 

1−

∑ L j

=

1

1

 L j =

1 − η UL

  N 0  W     E b   R j

1 + 

 j =1  j = M 

If we have M identical users:

 j =1

Noise Rise =

 M 

∑ L j =

 I total P N 

  N 0  W     E b    R j

1 + 

1  M 

=

1−

  N 0  W   1 +    E b    R j

The UMTS Air Interface 

Noise Rise and Loading Factor ▪

Capacity is linked to Eb/No value



Maximum Path Loss tolerated is linked to maximum NR Noise Rise

Loading Factor

1 dB 3 dB 6 dB 10 dB

20% 50% 75% 90%

Noise Rise = −10 log10 (1 − η UL )

The UMTS Air Interface 

Loading Factor Loading Factor =

Actual Throughput Pole Capacity

For  M  identical users with data rate  R : Loading Factor =

 MvR W 

  E b  (1 + i )   N   0   

  E b   M (1 + i )v   N   0    = W   R

The UMTS Air Interface 

UL Pole Capacity For large number of  users Pole Capacity ≈



  E b    (1 + i )   N 0

W = 3840000 Eb/No = 3 i = 0.5 Pole Capacity ≈

3840000

(3)(1 + 0.5)

= 853 kbps

• 50% of this would give a Noise Rise of 3 dB. •50% of 853 kbps = 426 kbps

The UMTS Air Interface 

DL Pole Capacity The Downlink benefits from orthogonality between channelisation codes.

Pole Capacity ≈



  E b    (1 − α + i )   N 0  

α is orthogonality factor and has a value between zero and 1.

The UMTS Air Interface 

1.3- Power Control and Handovers

The UMTS Air Interface 

Power Control and Near/Far Effect ▪







When a UE is near the NodeB it doesn’t need much power to reach it In the same manner, if a UE is far away it needs greater power to communicate with the NodeB Power Control is needed in the UL because a single overpowered mobile could block a Cell Power Control is also needed in the DL to provide far away users with enough power and to keep power low for near-by UEs

The UMTS Air Interface 

Soft and Softer Handover ▪







In UMTS it is possible to have a UE connected to more than 1 NodeB. This is called Soft Handover When in Soft Handover, the RNC can combine the best signals from the NodeB’s, hence providing a Soft Handover Gain Softer Handover applies when the mobile is being served by two cells on the same site. A Softer Handover gain also occurs. However, too many mobiles in Soft or Softer Handover could impose a significant Overhead on the system

The UMTS Air Interface 

Active Set and Pilot Pollution ▪







The Cells with which the UE is communicating form the UE’s Active Set This Active Set is made typically of 3 cells/pilot signals Any Pilot which is not a member of a UE’s Active Set and exceeds a certain threshold (typ. Ec/Io>-15dB) is considered a Polluter Pilot Pollution is a common WCDMA issue that needs to be sorted immediately

The UMTS Air Interface 

Summary of Key Concepts ▪

Processing Gain



Channelisation and Scrambling Codes



Ec/Io



Eb/No



Noise Rise



Cell Loading



Pole Capacity



Near/Far Effect



Soft and Softer Handover Gain

The UMTS Air Interface 

Summary of Key Formulas Eb/No



 E b  N 0 ▪

(dB ) =

 E c  I 0

+ Gp

Pole Capacity

UL Pole Capacity ≈



  E b    (1 + i )   N 0  

DL Pole Capacity ≈



  E b    (1 − α + i )   N 0  

2- The UMTS Link Budget

The UMTS Link Budget 

UMTS Link Budget vs. GSM’s ▪

Interference Margin for Noise Rise



Target Eb/no



Processing Gain (dBs) in UMTS = 10 log (3840000/User Rate (bps))



Power Control margin



Handover Gains

The UMTS Link Budget 

Interference Margin ▪

An admission control parameter. Same as “Noise Rise Limit”



Puts a limit to how many users can be taken in the UL



Has an associated Loading Factor: ▫

NR= 3dB, Load Factor=50%



NR=6dB, Load Factor=75%

The UMTS Link Budget 

Target Eb/No ▪

UMTS Link Budgets are made for Bearers



A UMTS service may use one or more Bearers, with each Bearer having a QoS Eb/No requirement



A typical Voice Bearer requires an Eb/No of 5dB



A typical 128 kbps Bearer requires and Eb/No of about 2dB

The UMTS Link Budget 

Processing Gain ▪

Depends on the bitrate of the Bearer



Helps with the required Ec/Io at the receiver



For a 12.2 kbps voice Bearer, Gp = 25dB



For a 128 kbps data Bearer, Gp= 15dB

The UMTS Link Budget 

Power Control (Fast Fading) Margin ▪

It’s entered to allow for adequate Power Control to compensate for Fast Fading



It’s dependent on the Speed Profile of the Mobile



At higher speeds, its smaller as the network cannot effectively compensate for Fast Fading

The UMTS Link Budget 

Handover Gains ▪

If a UE is in Soft or Softer Handover, this will provide Diversity Gains



These gains can help the Link Budget by helping in achieving the Target Eb/No with less power



This gain is dependent on the Delta on the Ec/Io of the involved paths

The UMTS Link Budget 

UL Link Budget ▪

Because UL power is lower than DL power coverage is “UL limited”.



Initially, most attention is paid to the UL budget.

The UMTS Link Budget 

-120 dBm Receiver Sensitivity ▪

Typical noise floor of cell receiver is -104 dBm.



Considering full rate voice (12.2 kbps) processing gain is 25 dB.



If target Eb/No is 5 dB and allowed Noise Rise is 4 dB then: ▫

UE must be capable of delivering (-104-25+5+4)= -120 dBm for a successful connection.



-120 dBm is effectively the receiver sensitivity for 12.2k voice.



For a 128kbps service, the Rec. Sensitivity is around -110dBm

The UMTS Link Budget 

UL Link Budget - voice ▪

If the UE can transmit at powers up to +21 dBm, the maximum link loss is: 21 - (-120) = 141 dB.



The maximum air interface path loss can be calculated by considering antenna gains and miscellaneous losses (e.g. feeder loss, body loss)



If antenna gain = 17 dBi and losses = 4 dB, then maximum path loss = 141 + 17 - 4 = 154 dB



Note: margins not considered (e.g. shadow fading, building penetration loss). These could total 24 dB.

The UMTS Link Budget 

Link Budget - voice Noise Floor Noise Rise Limit Processing Gain Target Eb/No Receiver Sensitivity UE Tx Power Maximum Link Loss Antenna Gain Feeder loss Body loss Maximum path loss Margins Target path loss

-104 dBm 4 dB 25 dB 5 dB -120 dBm +21 dBm 141 dB 17 dBi 3 dB 1 dB 154 dB 24 dB 130 dB

The UMTS Link Budget 

UL Link Budget - VT ▪

UMTS is introduced to offer higher level services such as video telephony (VT).



VT will typically operate at 64 kbit/s. ▫



Processing gain = 17.8 dB

If all other parameters remain the same, then the maximum path loss will be 154 - 25 + 17.8 = 146.8 dB.



Different service:- different range.



Typically range for voice = 1.6 x range for VT

The UMTS Link Budget 

UL Link Budget- 128 kbps Thermal Noise: -104 dBm, Noise Figure: 4 dB, Eb/No: 1.5 dB Processing Gain: 15 dB

(10 log[3840/128])

Receiver Sensitivity -113.5 dBm Max Link Loss = 21 dBm -(-113.5 dBm) = 134.5 Antenna Gains: 20 dBi

Feeder Loss: 3dB

Maximum Path Loss: 151.5 dB

Body Loss: 0dB

The UMTS Link Budget 

DL Link Budget- 128 kbps Allowable Path Loss: 151.5 dB Receiver Sensitivity -113.5 dBm Required Tx Power: 24 dBm per channel Eb/No= 1.5 dB, which in linear is = 0.5



10^(1.5/10)= 1.41

1+i = 1.5

DL Pole Capacity =

3.84 x103

(1.41)(1 + 0.5 − 0.6)

= 3Mbps

For 50% loading capacity = 1.5Mbps or 11- 128kbps channels 11 channels @ 24 dBm = 34.4 dBm

The UMTS Link Budget 

Conclusions ▪

Eb/No and capacity intimately linked.



Link budgets are affected by fast fading and interference margins.



Uplink and downlink affected differently by increased loading.



Flexibility allows high data rate services to be provided.



Asymmetric traffic requirements can be designed in.

3- Coverage Planning

Coverage Planning 

Coverage Objectives ▪

Achieve Minimum Pilot Coverage on Service Area



Minimum Coverage dependant on: ▫







ALP Services to be provided Loading

KPI’s ▫







RSCP (Ec) RSS (Io) Ec/Io Pilot Pollution (Scrambling Code overlapping)

Coverage Planning 

Factors affecting Coverage ▪





ALP is a function of: ▫

Clutter Type



Shadow Fading Margin

Services: ▫

The higher the bitrate the lower the coverage



Different Eb/No requirements

Loading: ▫

The higher the loading the lower the coverage



Loading factor tied to Noise Rise Limit

Coverage Planning 

3.1 Network Dimensioning

Coverage Planning 

Dimensioning Inputs Environment Site Configuration

Service

Demographic

Geographic

Coverage Planning 

Simple Coverage ▪

Link Budget based ▫

i.e. simple numerical calculation

Create Link Budget

Max PL ▪

Firstly a link budget is created Calculate Range



The maximum path loss is used to calculate the cell range using a propagation model

Max Range

Calculate Site Area





The cell range is used to calculate the site area Site Numbers = (Total Area)/(Site Area)

Max Area Calculate Number of Sites in a given Area

Coverage Planning 

Shadow Fading and Building Penetration ▪

Building Penetration ▫



P(connect) 50%

75%

Shadow Fading ▫

F u =

Mean and standard deviation per environment Typically calculated using ‘Jakes’

1  1 − 2ab    1 − ab   erf   1 −     1 − erf  (a ) + exp 2  b b 2          

Where: a =

( x0 − α ) σ 

2

;

0

  e     σ  2 

b = 10n log10 

x 0 - α  = Fade Margin σ = Standard Deviation of Model n = Propagation Model Exponent

P(connect)

x0 - α

76%

Point Location Probability Area Location Probability 5.6



90%

x0 - α

This assumes an isolated omni directional site…

Coverage Planning 

Environment Distribution ▪

Spreadsheets don’t deal with topology or morphology accurately ▫





Hills, parks and distributed target areas Interference and traffic captured by sites will vary

Margins for site acquisition and overlap are required Urban Area

Suburban Area Site Numbers

Site Numbers?

Coverage Planning 

3.2 Planning using Software Tools

Coverage Planning 

Pilot Power as an Indicator If pilot power is 33 dBm, the pilot strength on the ground is an indicator of link loss. 113 dB loss: -80 dBm pilot 120 dB loss: -87 dBm pilot

Popular indicator as drive test measurements report on pilot strength.

•> -80 dBm

•> -87 dBm

Coverage Planning 

Pilot Power as an Indicator issues Pilot powers not necessarily equal deployment of MHA at selected sites will alter target pilot values. ▪

Even if MHAs are universally deployed, their effect will depend on feeder loss. ▪

Generally, MHAs have a different effect on UL to DL, therefore DL measurement not a reliable indicator of UL performance. ▪

•> -80 dBm

•> -87 dBm

Coverage Planning 

Letting the tool do the work ▪

It is possible to define: The UE: in particular Tx Power



The bearer: bit rate and Eb/No.



Cell receiver: noise floor; noise rise; feeder loss; MHA characteristics. ▫

Margins required.



This allows maximum path loss to each cell to be determined and UL coverage to be calculated directly.



•VT coverage achieved

•Voice coverage achieved

Coverage Planning 

Assessing Interference with a Static Analyser - Ec/Io Pilot Ec/Io indicates pilot power as a ratio of total wideband power (including the pilot itself). ▪

Not terribly “scientific” but it corresponds directly to measurement reported by the UE in drive tests. ▪

Coverage Planning 

Assessing Interference with a Static Analyser - Pilot SIR Pilot SIR gives the quality of the pilot. ▪

Effect of orthogonality on own-cell interference is considered. ▫

Pilot power not considered as interference. ▫

Pilot SIR is always better than Ec/Io. ▪

Coverage Planning 

3.3 Overcoming Coverage Problems

Coverage Planning 

Limiting mutual interference

• Downtilt antennas. • Consider mounting antennas on the side of buildings.

Coverage Planning 

Limiting mutual interference 6ºElec 0ºMech 0º

0º 6º

0º 6º



0ºElec 6ºMech

-6º 6ºElec -6ºMech

6º 0º







0º 12º

Controlling the backlobe can produce a small but significant improvement in capacity.

Coverage Planning 

Limiting mutual interference • Key parameter: Frequency Re-use Efficiency (FRE).

FRE =

 N  Intra  N  Intra +  N  Inter 

 N  Intra is the intra - cell interference (W)  N  Inter  is the inter - cell interference (W)

Coverage Planning 

Mast Head Amplifiers (TMA’s) ▪

Used to lower the Noise Figure of the receiver



Can “offset” feeder losses



MHA used to increase coverage range



Typ. 1.6 dB Noise Figure (NF)



Typ. Gain of 12dB (adjustable)



Increase uplink capacity



Adds Insertion loss on DL (~ 1.3 dB) DC

BiasBias-T

Ant by pass TMA

Coverage Planning 

Uplink Receive Space Diversity ▪

Common to have two receive antennas per sector at the base station.



Even if highly correlated, coherent combination should yield ~3 dB improvement.



In practice a gain of 4 dB or more is expected from antennas spaced 2-3 m apart.

Receive antenna 2

Receive antenna 1

Coverage Planning 

Uplink Receive Space Diversity ▪

This is not “conventional” space diversity.



Each antenna is connected to a separate finger of the Rake receiver.







This is possible due to the synchronisation and channel estimation derived from the Pilot channel. Thus Eb/No is improved, rather than simply an effective power gain. Very low individual Eb/No will probably mean a very low pilot level which will lead to poor coherence and little gain - process becomes “self-defeating”.

Coverage Planning 

3.4 Coverage in the Real World

Coverage Planning 

Typical vendor values ▪

Pilot Power = 5-10% of Total Power



Control Channel Powers = 3-5 dB below Pilot ▫



(27-33 dBm)

CCPCH’s

Other signalling Channels = 3-5 dB below Pilot ▫



(30-35 dBm)

(27-33 dBm)

PICH, AICH, SCH’s

Summary: Total Non-Traffic Channels = 20-25% of total power

Coverage Planning 

Some additional constraints ▪

GSM existing coverage



GSM legacy sites



Antenna limitations: height, azimuths, etc.

4- Capacity Planning

Capacity Planning 

Capacity Objectives ▪

Manage effectively predicted Load on Service Area



Capacity dependant on:





Number of users



Position of users relative to the cell



Services demanded



UE Power Control

KPI’s ▫

Cell UL Load Factor



Cell DL Power

Capacity Planning 

Factors affecting Capacity ▪

Number of Users: The more users the more noise



Position of Users: The farther away, the more noise





Services demanded: The more high-bitrate users on the cell, the less overall number of users possible UE Power Control: Imperfect power control will account for more noise in the network

Capacity Planning 

Soft and Hard Capacity ▪





Hard Capacity: Hard limit imposed by actual channel elements Typ. 16 Kbps Channel elements. Also called “Resources” or “Cards” Soft Capacity: Variable, depending on Network loading

Capacity Planning 

UL Pole Capacity ▪

Capacity is typically limited on the UL



This is because, in the UL we don’t have Orthogonality to help us

UL Pole Capacity ≈



  E b    (1 + i )   N 0  

Capacity Planning 

UL Pole Capacity Exercise- Voice ▪

If we assume a service with Eb/No = 6dB and i = 0.8



Eb/No= 4 (linear)



If you consider 12.2 kbps Voice bearers: ▫

UL Pole Capacity= 533 kbps

533/12.2 = 43.7 Voice Trunks



Adding a typ. Voice activity factor (+overhead) of 58%



New number of voice trunks is 533/(12.2x0.58) = 75.3

Capacity Planning 

UL Pole Capacity Exercise- Voice ▪

A typical UMTS Cell can handle about 40E of Voice services



With 75.3E being 100% capacity, 40E = 53% Loading



Noise Rise= -10log (1-0.53) = 3.2dB



Typically, 25% of this capacity will be allocated to Soft Handover

Capacity Planning 

UL Pole Capacity Exercise- VT ▪

If we assume a service with Eb/No = 3dB and i = 0.8



Eb/No= 2 (linear)



If you consider 64 kbps VT bearers with 100% activity factors: ▫

UL Pole Capacity= 1066 kbps

1066/64 = 16.6 Voice Trunks



Comparing bitrates: 64kbps/7.1kbps = 9

(7.1= 12.2x0.58)



Comparing trunks: 75.3/16.6 = 4.5



Difference is due to different Eb/No’s 3dB (VT) vs 6dB (voice)

Capacity Planning 

4.1 Multi-Services Capacity and Capacity Dimensioning

Capacity Planning 

Multi-Service Capacity Eb/No

Activity Factors



Voice= [email protected]



58%



VT= [email protected]



100%



128PS= [email protected]



100%

dB vs Linear

Bitrate Ratios relative to voice



5.6dB= 3.6



(1x) 7.1 kbps



3.8dB= 2.4



(9x) 64 kbps



2.8dB= 1.9



(18x) 128 kbps

Capacity Planning 

Campbell’s Spreadsheet CS

CS

PS

PS

PS

Bearers (kbps)

12.2

64

64

128

384

CS user per cell

30

3

Not Applicable

Not Applicable

Not Applicable

Not Applicable

Not Applicable

0

0

0

58.0%

100.0%

0.0%

0.0%

0.0%

7.1

64.0

0.0

0.0

0.0

6

3

2

1.2

1.8

3.98

2.00

1.58

1.32

1.51

1

0.50

0.40

0.33

0.38

212.28

192

0.00

0.00

0.00

PS Capture Data (Mbytes/hour) Activity factor Average rate (kbps) Eb/No Eb/No ratio Relative Ratio Equivalent data rate (voice)

Factor for i

0.8

Reference Pole Capacity (kbps)

536

Loading of Cell

75.4%

UL Noise Rise (Loading)

6.10

Capacity Planning 

Traffic Exercise ▪

Manchester pop. = 2.2 Million



Mobile [email protected]% = 1.76 Million



For an operator with 25% market share = 440K Subs



With an avg voice traffic of 35mE per users = 15,400 Erlangs



Considering 30E per cell = 513 Cells or 171 Sites



This with 52% loading and 2% GOS

Capacity Planning 

Simple Capacity Dimensioning ▪









Capacity calculation based Calculate maximum capacity per carrier Calculate maximum offered traffic per sector Calculate site area based on traffic density

Calculate Carrier Capacity

Calculate Sector Offered Traffic

Calculate Maximum Site Area

Calculate Number of Sites in a Given Area

Calculate the maximum number of sites in an area

Capacity Planning 

Other Dimensioning Factors ▪

GSM/UMTS Interaction Proportion a percentage of voice traffic to GSM Don’t assume that UMTS carries all of the traffic ▫





Microcells Offer capacity relief to macrocells This allows macrocells to be larger, potentially with a lower loading ▫





Repeaters Extend the coverage of macrocells at a lower cost than adding a new Node-B ▫

Capacity Planning 

“2G” analysis ▪

Coverage thresholds can be set for various services and coverage examined in a similar manner to that for GSM systems



Traffic captured by cells for GSM traffic can be interpreted as cell loading for UMTS systems.

Capacity Planning 

4.2 Analysis of DL Capacity

Capacity Planning 

DL Pole Capacity DL Pole Capacity ≈



  E b    (1 − α  + i )   N 0  



The Downlink must be able to match uplink capacity



If i=0.6 and Eb/No is 6 dB; pole capacity is 960kbps.



At 50% loading UL capacity is 480 kbps (39 voice).

Capacity Planning 

Further Analysis of the Downlink ▫

Minimum Rx power (25 dB processing gain, 3 dB Noise figure) = -104 + 3 + 6 - 25 = -120 dBm



If maximum Tx power is 21 dBm, then 141 dB link loss can be tolerated. Can DL support this?



For every user that’s “allowed” in the UL, the Cell will have to provide enough power to support it on the DL

Capacity Planning 

4.3 Traffic Planning

Capacity Planning 

Traffic Density ▪





Traffic Density is forecast in terms of a density in terms of Erlangs per square kilometre. Different forecasts are given for different clutter categories. Knowing the clutter categories in the required service areas allows traffic to be simulated. Traffic Density Weightings 1 4

2 3

Clutter Category 1: Clutter Category 2: Clutter Category 3: Clutter Category 4:

10 50 30 10

Capacity Planning 

Density versus Numbers ▪



It is important to realise that the weightings are in terms of terminal densities. Sometimes the clutter category with the highest weighting occupies a small percentage of the area.

Area Weightings

1 4



Weighting of Actual Traffic per Category

3 2 3

Clutter Category 1: Clutter Category 2: Clutter Category 3: Clutter Category 4:

28 16 28 28

Clutter Category 1: Clutter Category 2: Clutter Category 3: Clutter Category 4:

Notice that the actual traffic volume per category differs from the traffic density. Traffic density is the parameter entered in the simulation tool.

4.4 Capacity Plots

12.7 36.4 38.2 12.7

Capacity Planning 

Coverage vs. Capacity Coverage vs. Capacity    ) 170.00    B    d    ( 165.00    s    s    o 160.00    l    h    t    a    P 155.00    m    u 150.00    m    i    x    a 145.00    M

Uplink Dow nlink

100

200

300

400

500

600

700

800

Throughput (kbps)

Capacity Planning 

Link Loss vs. Capacity 1200    ) 1000    s    /    t    i    b 80 0    k    ( 60 0    y    t    i    c    a 40 0    p    a 20 0    C

0 120

130

140

150

160

Link Loss (dB) +37 dBm

+40 dBm

+43 dBm

+46 dBm

Capacity Planning 

Orthogonality vs. Capacity 1200    ) 1000    s    /    t    i    b 800    k    ( 600    y    t    i    c    a 400    p    a 200    C

0 0

0.2

0.4

0.6

0.8

1

Orthogonality BTS Power: 37 dBm

40 dBm

43 dBm

46 dBm

Capacity Planning 

Out of Cell Interf. vs. Capacity 1400    ) 1200    s    /    t    i 1000    b    k    ( 80 0    y    t    i 60 0    c    a 40 0    p    a    C 20 0 0 0

0.4

0.8

1.2

1.6

Out of Cell Interference BTS Power: 37 dBm

40 dBm

43 dBm

46 dBm

2

Capacity Planning 

Capacity Planning Summary ▪

Capacity dependant on: ▫

Number of users



Position of users relative to the cell



Services demanded



UE Power Control



Multiple Services Traffic characteristic of UMTS



Pole Capacity, UL Cell Loading and DL Cell Power



Erlangs vs. Number of Terminals

5- UMTS-GSM Co-location Issues

GSM Co-location 

Co-location main Issues ▪

Have to live with existing GSM sites



Have to live with existing antenna heights/azimuths



GSM Interference: GSM1800, GSM1900, etc



Different coverage extents

GSM Co-location 

Interference Issues ▪



Interference can occur: ▫

between carriers



between operators



between systems

Co-location of GSM and UMTS sites raises special problems.

GSM Co-location 

3rd Generation Spectrum Allocations 1885

ITU

1980

IMT-2000

MSS

Land Mobile

(WARC-92)

1880 1900 1920

Europe

UMTS

GSM 1800

DECT

Unpaired

Japan

1980

Paired UL

2110

IMT-2000

20102025 UMTS

SAT

Unpaired

2110

1850

PCS

1800

1850

Land Mobile DL 2110 IMT-2000 2170

Land Mobile DL

PCS

1990

1950

2200

2110

Reserved

DL

1900

SAT

Land Mobile UL IMT-2000 1980

2200

UMTS

2110 IMT-2000 2170

1910 1930

UL

2170

Paired DL

Land Mobile UL

USA

UMTS

2200

MSS

Land Mobile

Land Mobile

UMTS

2170

IMT-2000

1920 IMT-2000 1980

1920

Korea

UMTS

20102025

2000

2050

2100

2150

2200

GSM Co-location 

Intersystem Interference Issues ▪

Wideband Noise - unwanted emissions from modulation process and non-linearity of transmitter



Spurious Emissions - Harmonic, Parasitic, Inter-modulation products



Blocking - Transmitter carriers from another system



Inter-modulation Products - Spurious emission, specifications consider this in particular ▫





Active: non-linearities of active components - can be filtered out by Cell Equipment Passive: non-linearities of passive components - cannot be filtered out by Cell Equipment

Other EMC problems - feeders, antennas, transceivers and receivers

GSM Co-location 

Isolation Requirements GSM 900

GSM 1800

UMTS

Receiving band 890 – 915 MHz 1710 – 1785 MHz (UL) Transmitting band 935 – 960 MHz 1805 – 1880 MHz (DL)

1920 – 1980 MHz 2110 – 2170 MHz

For example example - To prevent UMTS BTS blocking: with transmit power = 43 dBm Max level of interfering signal for blocking = -15 dBm in UMTS

Isolation required = 58 dB

1805 MHz 1710 MHz

1785 MHz

GSM 1800 Rx

2110 MHz

1880 MHz 1920 MHz

1980 MHz

UMTS Rx

GSM 1800 Tx

2170 MHz

UMTS Rx

GSM Co-location 

Typical Isolation Requirements Isolation Requirements Specification Requirements

GSM UMTS Tx to UMTS Tx to UMTS Tx 900/GSM1 GSM 900 GSM 1800 to UMTS 800 to Rx Rx Rx UMTS Rx

Blocking isolation

58 dB

40 dB

48 dB

63 dB

Spurious emissions/inter -modulation products

39 dB

34 dB

34 dB

39 dB

GSM Co-location 

Achieving Isolation Requirements ▪

GSM

Isolation can be provided in a variety of different ways. UMTS ▫



By antenna selection and positioning.

GSM Filter

By filtering out the interfering signal. UMTS



GSM

By using diplexers and triplexers with shared feeder and multiband antennas.

Diplexer

UMTS

6- Practical Examples

Practical Examples 

Small, isolated cell ▪

Traffic is spread across a small area with low path loss to the base station. The cell is heavily loaded. Eb/No and Ec/Io failures are



associated with path loss.

Noise Rise will be the only radio-



related cause of failure.

Practical Examples 

Small, isolated cell ▪

Capacity improvements can be achieved by: ▪

Increasing Noise Rise limit.



Reducing target Eb/No on the uplink and the downlink.



A Mast Head Amplifier will not be of much use as uplink Eb/No is not a significant cause of failures.

Practical Examples 

Large, isolated cell ▪

As loading increases, meeting Eb/No targets will be a problem.



Heavy loading will result in Cell Breathing. Users at a great distance from the base station will not be able to make a connection.



Gaps will appear in network coverage.



Practical Examples 

Sectored Sites ▪

Capacity will be affected by overlap of cell coverage areas.





Cell overlap can be controlled by pointing of antennas.

Combining mechanical and electrical tilt can control backlobe radiation.

Practical Examples 

Pilot Pollution ▪

A mobile can be too well served.







It may be impossible to decode a dominant pilot. Ec/Io and Eb/No failure due to cochannel interference. Scaling pilot power and controlling radiation patterns is vital.

Practical Examples 

Soft Handover ▪

Soft handover regions must be controlled to ensure that capacity is maximised. ▪

Handover margin can be adjusted.



Pilot powers can be scaled.



Effect on handover region can be monitored.

Practical Examples 

Dimensioning and Simulating a Network ▪







We are able to approximately dimension a network with a simple spreadsheet.

This is a simplified network not considering the effects of mapping data and uneven traffic distribution.

However, it is possible to simulate such a simplified network so that a clear understanding of the working of the simulator can be established.

The network can then be modified to incorporate practical features such as terrain features and traffic distribution.

6.1 Simulation Examples

Practical Examples 

The Network and Height Profile ▪

3dB NR limit



20m antennas





No MHA, no RX diversity

500 Terminals spread on Urban and Suburban areas

Practical Examples 

Voice- Reason for Failure ▪



Polygon area OK as far as Voice Service

Some NR Limit reached failures (aqua pixels)

Practical Examples 

VT- Reason for Failure ▪





Polygon area shows UL Eb/No failures

NR Limit reached failures (aqua pixels)

Changing azimuths on site to the right of polygon is not an option due to existing traffic restrictions

Practical Examples 

VT- NR Limit increased to 6dB ▪





NR limit parameter changed from 3 dB to 6 dB on all cells

NR Limit reached problem fixed

UL Eb/No problem still there

Practical Examples 

Pilot Coverage for Polygon ▪



Looking for the causes of the failure, a Pilot Coverage plot is done

It can be seen that Pilot level in Polygon area is very low (around -105 dB)

Practical Examples 

Height Profile for Polygon ▪



Looking for the causes poor coverage, a Height Profile is performed It can be seen that there is a significant obstruction preventing a good UL

Practical Examples 

Height increased to 40m ▪





Trying to fix the UL Eb/No failure, antenna height is increased from 20m to 40m

This decreases the pathloss, however, the original problem is not solved

No interference problems are created either

Practical Examples 

Adding MHA and RX Diversity ▪





Another option is to add an MHA and RX Diversity

These additions prove the solution for most of the problem pixels inside the polygon

Height is still 40m, due to obstructions and poor site location

View more...

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