4 WCDMA Radio Network Planning

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    Wideband CDMA

    Radio Network Planning

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    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)

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    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 (suchas number of BSs and RNCs)

    These estimations will be based on the operators

    requirements on coverage, capacity and quality ofservice.

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    WCDMA-specific parameters in the link budget

    compared to those parameters used in a TDMA-basedradio systems are:

    1. Interference margin

    The value of the interference margin used in the linkbudget depends on the loading of the cell.

    Higher is the value of the interference margin in theuplink, the smaller is the coverage area. Typical valuesare 1.0-3.0 dB in the coverage-limited cases,

    corresponding to 20-50% loading.

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    2.Fast fading margin

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

    3.Soft handover gain

    Due to uncorrelated channels from the MS to the BSs,handover gives a gain against slow fading. Also, softhandover gives an additional macro diversity gain

    against fast fading. The total handover gain can beassumed to be in the range of 2.0-3.0 dB.

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    Link budget approach

    Coverage requirement for a specific data rate with uniform load

    Derive Link Budget

    Coverage satisfied?

    Input existing 2G sites that can be

    Upgraded to 3G

    Refine design, put new sites using

    Planners individual judgment

    End

    No

    Yes

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    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

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    14 dBiBase station antenna gainP

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

    5 dBRequired Eb/NoN

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

    12.2 Kb/sData rateL

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

    3 dBInterference Margin (noise rise)J

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

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    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

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    Cell range

    From the link budget, the cell range Rcan be easily calculatedusing a known propagation model, for example the Okumura-Hatamodel. The Okumura-Hata propagation model for an urbanmacro-cell with base station antenna height of 30m, mobile antennaHeight of 1.5m and carrier frequency of 1950 MHz is given by:

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

    For suburban areas we assume an additional area correction factorof 8 dB and therefore the path loss is:

    L = 129.4 + 35.2

    )(log 10 R

    )(log 10 R

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    Some DefinitionsRatio 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.)

    own

    other

    I

    Ii

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    For the downlink, i is defined as:

    i =

    where is the power received from other BSs andpj is the power

    received from the serving BS.

    Noise rise

    noise rise =

    j

    other

    P

    I

    N

    Notherownj

    N

    total

    P

    PIIP

    P

    I

    otherI

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    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,jis the received signal power for mobile userj,is the activity factor of userj, Rjis the bit rate of userj and the

    total received wideband power including thermal noise power in the BS.totalI

    jrtotal

    jr

    jj PI

    P

    RW

    jo

    bN

    E,

    ,

    j

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    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

    jjR

    joN

    bE

    wjrP

    1

    1,

    totaljjr ILP

    ,

    jL

    jL

    jjR

    joN

    bE

    wjL

    1

    1

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    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

    NP

    totalI

    N

    j

    totalIj

    LN

    j

    jrP

    NP

    totalI

    11

    ,

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    Noise rise (6)

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

    (7)

    when becomes close to 1, the corresponding noise rise approaches

    to infinity and system has reached its pole capacity.

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

    can write

    N

    jj

    LUL1

    UL

    ULN

    jj

    N

    total

    LP

    I

    11

    1

    1

    1

    UL

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    (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 allvoice service network, where all N users in the cell have

    a low bit rate ofR, we can write

    1

    RN

    EW

    o

    b

    UL

    N

    j

    jjR

    oN

    bE

    W

    N

    j

    iLi

    j

    jUL

    11

    1

    1

    )1()1(

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    and hence equation (9) is simplified to

    )1( iNR

    W o

    NbE

    UL

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    - Downlink load factor

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

    In the absence of interferences, we definedand hence,

    NP

    jrP

    jRj

    W

    joN

    bE ,

    NPjLjrP ,

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    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 own

    cell base station power, received by the mobile user j.

    jR

    WjoN

    bEjj

    ijj

    L1

    1

    j

    j

    ji

    jR

    Wj

    joNb

    E

    P

    jrP

    jLN

    1,

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    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

    ji

    j

    j

    RW

    joNbEN

    jj

    1

    1

    N

    jj

    LDL

    1

    j

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    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.

    i

    jR

    W

    joN

    bE

    N

    j

    jDL

    1

    1

    DL

    1log10

    DL

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    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

    jR

    W

    joN

    bE

    jP

    ,

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    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

    joN

    bEj

    LWoN

    totalP

    1

    1

    oN

    FKTN oo

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    Throughput per cell

    whereNis the number of users per cell,R is the bit rate and

    is the block error rate.

    BLERRNThroughout 1

    BLER

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    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 WCDMAwhere 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

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    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 andnetwork parameters.

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    Static simulation approach

    Coverage/traffic/QoS requirements

    Input existing 2G sites which can be

    upgraded to 3G

    Refine design, put new sites using

    Planners individual judgment

    WCDMA static simulator

    Coverage/capacity/QoS

    Satisfied?

    End.

    No

    Yes

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    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

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    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.

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    Network optimiser

    Feed in your site portfolio

    Set optimisation criteria

    Run Optimiser algorithms

    End

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    Optimisation phase

    Coverage information

    WCDMA FDD

    parameters

    Traffic information

    Site locations

    Optimisation criteria

    Optimiser

    Optimised site

    locations

    Coverage,

    Capacity/QOS

    statistics

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    Reference

    WCDMA for UMTS, Edited by Harri Holma and Antti Toskala,

    Second edition, John Wiley & Son Ltd, ISBN 0-470-84467-1.