Section 6 Wideband CDMA Radio Network Planning

Radio Network Planning

A radio network planning consists of three phases:

1. Network Dimensioning (using link budgets)

2. Detailed capacity and coverage planning (using planning tools)

3. Network optimisation (using optimisation tool)

Phase 1 :Network Dimensioning

• Dimensioning the WCDMA radio network includes radio link budget and coverage analysis, capacity estimation and estimation of the amount of network equipment (such as number of BSs and RNCs) required.

• These estimations will be based on the operator’s requirements on coverage, capacity and quality of service.

• WCDMA-specific parameters in the link budget compared to those parameters used in a TDMA-based radio systems are:

-Interference margin The value of the interference margin used in the link

budget depends on the loading of the cell. Higher is the value of the interference margin in the uplink, the smaller is the coverage area. Typical values are 1.0-3.0 dB in the coverage-limited cases, corresponding to 20-50% loading.

-Fast fading margin

For slow-moving mobiles, to take care of fast fading effect, a fast fading margin in the range of 2.0-5.0 dB should be included in the link budget.

-Soft handover gain

Due to uncorrelated channels from the MS to the BSs, handover gives a gain against slow fading. Also, soft handover gives an additional macro diversity gain against fast fading. The total handover gain can be assumed to be in the range of 2.0-3.0 dB.

Link budget approach

Coverage requirement for a specific data rate with uniform load

Derive Link Budget

Coverage satisfied?

Input existing 2G sites that can beUpgraded to 3G

Refine design, put new sites usingPlanner’s individual judgment

End

No

Yes

Uplink Link Budget Example

3.84 Mchip/sChip rateH

-169 dBm/HzReceiver noise density (E+F)G

5 dBBase station receiver noise figureF

-174 dBm/HzThermal noise densityE

18 dBmMobile EIRP (A+B-C)D

3 dBBody lossC

0 dBiMobile antenna gainB

21 dBmMobile transmit power (125 mW)A

14 dBiBase station antenna gain P

-120.2 dBmBase station receiver sensitivity (K-M+N) O

5 dBRequired Eb/No N

25 dBProcessing gain (10 log (H/L) )M

12.2 Kb/sData rate L

-100.2 dBmTotal effective noise & interference (I+J) K

3 dBInterference Margin (noise rise) J

-103.2 dBmReceiver noise power (G + 10log H)I

137.2 dBMaximum path loss for cell range

(D-O+P-Q-R-S+T)U

4 dBSoft handover gainT

8 dBIn-car lossS

9 dBLognormal shadowing marginR

2 dBCable losses in the base stationQ

Cell range From the link budget, the cell range R can be easily calculated using a known propagation model, for example the Okumura-Hata model. The Okumura-Hata propagation model for an urban macro-cell with base station antenna height of 30m, mobile antenna Height of 1.5m and carrier frequency of 1950 MHz is given by:

L = 137.4 + 35.2 where L is the path loss in dB and R is the cell range in Km.

For suburn areas we assume an additional area correction factor of 8 dB and therefore the path loss is:

L = 129.4 + 35.2

)(log10 R

)(log10 R

Some Definitions• Ratio of other cell to own cell interference In the uplink, it is calculated for the BS, therefore i is similar for all connections within one cell. However in the downlink, it is calculated for each MS and therefore depends on the MS location. i ranges from 0.15 (very well isolated microcells) to 1.2 ( poor radio network planning.)

i

own

othIIi

For the downlink, i is defined as:

i =

where is the power received from other BSs and pj is the power received from the serving BS.

• Noise rise noise rise =

j

otherP

I

N

Notherownj

N

totalP

PIIP

PI

otherI

Capacity estimation The second part of dimensining is to estimate the capacity per cell i.e., supported traffic per BS. The capacity per cell depends on the amount of interference per cell, hence it can be calculated from the load equations.- Uplink load factor equation

(1) where W is the chiprate, pr,j is the received signal power for mobile user j, is the activity factor of user j, Rj is the bit rate of user j and the total received wideband power including thermal noise power in the BS.

totalI

jrtotal

jr

jj PI

P

RW

jo

bN

E,

,

j

Equation (1) can be rewritten as: (2)

we define

where is the load factor of one connection.

Using this equation and equation (2), one can obtain as:

(3)

totalI

jjRjoNbE

wjrP

1

1,

totaljjr ILP ,

jL

jL

jjRjoNbE

wjL

1

1

The total received interference, excluding the thermal noise ,canbe written as:

(4)

The noise rise is defined as:

Noise rise (5)

and using (4), we can obtain

NP

NPtotalI

N

jtotalIjL

N

jjrPNPtotalI

11,

Noise rise (6)

where is defined as the uplink load factor and equals to:

(7)

when becomes close to 1, the corresponding noise rise approachesto infinity and system has reached its pole capacity.

If the interference from the other cells is taken into account, then one can write

N

jjLUL

1

UL

ULN

jj

N

total

LP

I

11

1

1

1

UL

(9)

where i is the ratio of other cells to own cell interference.The interference margin used in the link budget must be equal to the maximum planned noise rise i.e., -10 log(1- ).

For an all – voice service network, where all N users in the cell have a low bit rate of R, we can write

1

RN

EW

ob

UL

N

j

jjRoN

bEW

N

jiLi

j

jUL

111

1)1()1(

and hence equation (9) is simplified to

)1( iNR

WoN

bE

UL

- Downlink load factor

In the absence of intra- and inter- cell interferences, one can write

In the absence of interferences, we defined and hence,

NPjrP

jRj

W

joNbE ,

NPjLjrP ,

when we take into account both intra- and inter- cell interferences, we have

where is the orthogonality of the channel of mobile user j.Its value depends on the channel multipath fading ; where = 1 means no multipath fading. is the ratio of other cell to owncell base station power, received by the mobile user j.

jRWjoN

bEjjijjL

11

jj

ji

jRW

jjoN

bEP

jrP

jLN

1,

The downlink load factor is defined as:

since, in the uplink, i and depends on the location of the mobile user and they should ; therefore, be approximated by their average values across the cell, and .

jji

jij

jRW

joNbE

N

jj 1

1

N

jjLDL

1

j

The average value of the downlink load can then be approximated as:

the noise rise is given by:

noise rise Interference margin

when 1 noise rise

the system approaches its pole capacity.

ijR

WjoN

bE

N

jjDL

11

DL1log10

DL

Total BS transmission power The total BS transmission power can be written as:

where is the average attennation between the BS and mobile receiver (6 dB less than the maximum path loss) since

DL

N

jjrPL

totalP

11

,

L

Njr P

jRW

joNbE

jP

,

and then

where is the power spectral density of the mobile receiver and is given by:

where F is the noise figure of the mobile receiver with typical values of 5-9 dB.

WNP oN

DL

N

jjR

W

joNbE

jLWoN

totalP

1

1

oN

FKTN oo

Throughput per cell

where N is the number of users per cell, R is the bit rate and is the block error rate.

BLERRNThroughout 1

BLER

Link budget approach

• Pros - Enables fast planning of coverage for a pre-specified uniform load - Skilled 3G staff not a requirement

• Cons - Too simplistic for WCDMA where coverage/capacity/QoS are closely related - The final performance of the network cannot be derived based on this method - Mix of traffic cannot be taken into account

Phase2 :Detailed capacity and coverge planning

• In this phase, real propagation data from the planned area and the estimated user density and user traffic are used.

• The output of this phase are the base station locations, configuration and network parameters.

Static simulation approachCoverage/traffic/QoS requirements

Input existing 2G sites which can beupgraded to 3G

Refine design, put new sites usingPlanner’s individual judgment

WCDMA static simulator

Coverage/capacity/QoSSatisfied?

End.

No

Yes

Static simulation approach•Pros - Average QoS, capacity and coverage may be assessed for a mix of traffic

•Cons - Can only be run on a limited area, typical figures for running time for a 3 Km x 3 Km area is ~5-8 hours on a Unix work station - Manual judgment must be exercised in interpreting the results and making decisions to improve the plan. - Plans may need to be iterated several times (on average 5 times) before the desired capacity/QoS/ coverage is achieved. This takes total planning time for a 3 Km x 3 Km to ~1 to 2 working days at best! - Skilled 3G a prerequisite

Phase 3 : Optimisation Phase

Network optimiser

•Optimises WCDMA FDD network plan minimising the number of sites required to achieved the coverage/traffic/QoS targets set by the user. •An Optimiser also automatically selects the most appropriate antenna tilt, direction and sectorisation in order to achieve the required coverage/traffic/QoS.

Network optimiser

Feed in your site portfolio

Set optimisation criteria

Run Optimiser algorithms

End

Optimisation phase

Coverage information

WCDMA FDDparameters

Traffic information

Site locations

Optimisation criteria

Optimiser

Optimised sitelocations

Coverage,Capacity/QOS

statistics

Reference “WCDMA for UMTS”, Edited by Harri Holma and Antti Toskala, Second edition, John Wiley & Son Ltd, ISBN 0-470-84467-1.