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 ≈
W
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 ≈
W
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 ≈
W
E b (1 + i ) N 0
DL Pole Capacity ≈
W
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
i
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
6º
0ºElec 6ºMech
-6º 6ºElec -6ºMech
6º 0º
0º
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 ≈
W
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= 3.8dB@64kbps
▪
100%
▪
128PS= 2.8dB@128kbps
▪
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 penetration@80% = 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 ≈
W
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
