Ericsson WCDMA Radio-Coverage

4. WCDMA Radio Coverage

4 WCDMA Radio Coverage 

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OBJECTIVES: On completion of this chapter the student will be able to:

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•

Explain free space path loss.

•

Use Okumura-Hata and COST 231-Walfish-Ikegami 231-Walfish-Ikegami propagation formulas.

•

Explain the concept of log normal fading and how it is incorporated incorporat ed in WCDMA coverage calculations.

•

Calculate the sensitivity of a RBS for various services,

•

Perform link budget budget calculations for the uplink of a WCDMA system. system.

•

Use simulation simulation graphs to calculate the downlink downlink coverage coverage and and capacity capacity of a WCDMA cell.

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Contents RADIO WAVE WAVE PROPAGA PROPAGATION TION............ ......................... .......................... .......................... ..................... ........ 86 OKUMURAOKUMURA-HATA HATA PROPAGATION PROPAGATION FORMULA FORMULA .................................. ............................................ .......... 89 COST 231-WALFISH-IKEGAMI 231-WALFISH-IKEGAMI PROPAGATION FORMULA ................... .......... ............. .... 89 SIGNAL SIGNAL VARIATIONS VARIATIONS .................................. ................................................... .................................. ............................... .............. 90 POWER CONTROL MARGIN (PCMARG) .................................. ................................................... ...................... ..... 95 BODY LOSS (BL)......................... (BL).......................................... .................................. .................................. ............................... .............. 96 CAR PENETRAT PENETRATION ION LOSS (CPL)................ (CPL)................................. .................................. ............................... .............. 96 ANTENNA SYSTEM CONTROLLER (ASC) INSERTION LOSS (LASE) ...... ......... ... 96 FEEDER AND JUMPER LOSSES (LF+J) ................................. .................................................. ...................... ..... 97 RBS SENSITIVITY (RBSSENS) .................................. .................................................... ................................... ................... .. 98 UPLINK UPLINK LOAD ................................ ................................................. .................................. .................................. .......................... ......... 102

LINK BUDGET CALCULATION CALCULATION FOR UPLINK................ UPLINK ................................ .................. 103 MAXIMUM PATH LOSS (LPATHMAX)............................................... ).............................................................. ............... 104 WCDMA WCDMA CELL RAN RANGE................... GE.................................... .................................. .................................. .......................... ......... 106 SITE COVERAGE COVERAGE AREA .................................. ................................................... .................................. ......................... ........ 107

DOWNLINK DOWNLINK DIMENSIONING DIMENSIONING ..................... ............................... ..................... ..................... ................. ....... 109 DOWNLINK DOWNLINK LINK BUDGET BUDGET ................................... .................................................... .................................. .................... ... 110

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RADIO WAVE PROPAGATION In this course, we are primarily interested in the transmission tr ansmission loss between two antennas: the transmitter/emitter and the receiver. Many factors, including absorption, refraction, reflection, r eflection, diffraction, and scattering affect the wave propagation. However, in free space an electromagnetic wave travels indefinitely if unimpeded. This does not mean there are no transmission losses, as we will see in this first f irst simple model where isotropic emission from the transmitter and line of sight between the two antennas separated by a distance, d , in free space are assumed (Figure 4-1).

d Figure 4-1 Free space path loss 

Since an isotropic antenna, by definition, distributes the emitted power, P t t,  equally in all directions, the power density, S r r,  (power 2  per area unit) decreases as the irradiated area, 4 π  d πd      , at distance d , increases, that is: S r 

=

Pt 

4π d 2

If the transmitting antenna has a gain, G t t,  it means that it is concentrating concentrating the radiation towards the receiver. The power density at the receiving antenna increases with a factor proportional proportional to G t t,  that is: S r 

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=

Pt G t 

4π d 2

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The power received by the receiving antenna, P r r,  is proportional to the effective area, Ar , of that antenna, that is: Pr

= S ⋅A r

r 

It can be shown that the effective area of an antenna is proportional proportional to the antenna gain, G r r , and the square of the wavelength, λ , of the radio wave involved, that is: 2

 Ar 

=

Gr λ 

4π 

and, hence, the received power becomes 2

Pr 

=

Pt Gt Gr λ 

( 4π d ) 2

The transmission loss can be calculated as the ratio between the transmitted power and received power, that is: loss

=

Pt  Pr 

=

( 4π d ) 2 2

Gt Gr λ 

Radio engineers work with the logarithmic unit dB so the transmission loss, L, then becomes

 ( 4π d )   4π d     = 20 log   L = 10 log( loss) = 10 log  −  − 10 log(G ) − 10 log(G )     λ     G G λ    2

2

t

r

t 

r 

Radio engineers treat the antenna gains, 10log(G  10log(G r r)  and 10log (G  ( G t t ), separately, so that what is given in the literature as the path loss, Lp , is only the term 20log(4  20log(4 π  d πd/    / λ  λ). )  . In clearer terms, the path loss in free space is given by equation 14 below.

Free Space Path loss

 4π d   L p = 20 log     λ   

Equation 14 Free space path loss 

Note that the wavelength dependency of the path loss does not correspond to losses in free space as such. It is a consequence of the finite effective receiver area.

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This transmission loss expression is fairly general. The only thing t hing which changes when we improve our models is the expression for the path loss. The antenna gain is normally given in dB(i), that is, as 10log(G  10log(G ), ), where gain means a reduction of the total transmission loss, L, between a transmitting tr ansmitting and receiving antenna. This model helps us to understand the most important features of radio wave propagation. That is, the received power decreases when the distance between the antennas increases and the transmission loss increases when the wavelength decreases (or alternatively when the frequency increases). For cell planning, it is very important to be able to estimate the signal strengths in all parts of the area to be covered, that is, to predict the path loss. The model, described in this section, can be used as a first f irst approximation. However, However, more complicated models exist. Improvements can be made by accounting for:

• • • •

The fact that radio waves are reflected reflected towards the earth’s surface. Transmission losses, due to obstructions obstructions in the line of sight. sight. The finite radius of the curvature of the earth. The topographical topographic al variations in a real case, as well as the different attenuation properties of different terrain types, such as forests, urban areas, etc.

The best models used are semi-empirical, that is, based on measurements measurements of path loss/attenuation in various terrain. The use of such models is motivated by the fact that radio propagation cannot be measured everywhere. However, if measurements are taken in typical environments, the parameters of the model can be fine-tuned so that the model is as good as possible for that particular type of terrain. Two common propagation formulas are ‘Okumura-Hata’ (equation 15) and COST 231- Walfish-Ikegami (equation 16)

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OKUMURA-HATA PROPAGATION FORMULA

Lpath = A - 13.82logHb +(44.9-6.55logHb)logR - a(H m) [ dB ] Equation 15 Okumura-Hata Propagation formula 

where A = 155.1 for urban, A = 147.9 for suburban and semi-open areas A = 135.8 for rural, A = 125.4 for open areas. Hb = base station antenna height [m] Hm = UE antenna height [m] R = distance from transmitter [km] a(Hm) = 3.2(Log(11.75*H 3.2(Log(11.75*Hm))2- 4.97 or for 1.5m antenna a(1.5) = 0

COST 231-WALFISH-IKEGAMI PROPAGATION FORMULA

Lpath = 155.3 + 38logR – 18log(Hb – 17)

[dB]

Equation 16 COST 231-Walfish-Ikegami propagation formula 

where Hb = base station antenna height [m] R = distance from transmitter [km]

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SIGNAL VARIATIONS  The models, described in the previous section, can be used to estimate the average signal level (called the “global mean” mean”) at the receiving antenna. However, a radio signal envelope is composed of a fast fading signal super-imposed on a slow fading signal as shown in Figure 4-2 below. SS at Rx-antenna

Variations due to Rayleigh fading

Variations Variations due to Shadowing Shadowing (Local (Local mean)

Distance

Received Signal Level from formulae formulae (Global (Global mean) m ean)

Figure 4-2 Signal Variations 

These fading signals are the result r esult of obstructions and reflections. They yield a signal, which is the sum of a possibly weak, direct, line-of-sight signal, and several indirect, or reflected signals. The short term or fast fading (Rayleigh fading) signal (peak-topeak distance ≈ λ   /2) is usually present during during radio communication, communication, due to the fact that the mobile antenna is lower than the surrounding structures, such as trees and buildings. These act as reflectors. r eflectors. The resulting signal consists of several waves with various amplitudes and phases. Sometimes these almost completely cancel out each other. This can lead to a signal level below the receiver sensitivity. In open fields where a direct wave is dominating, this type of fading is less noticeable.

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The first and most simple solution is to use more power at the transmitter(s), thus providing a fading margin. Another way to reduce the harm done by Rayleigh fading is to use space diversity, which reduces the number of deep fading dips. Diversity means that two signals are received which have slightly different “histories” histories” and, therefore, the “best” best” can be used, or even better: the two can be combined. The signal variation received, if we smooth out the short-term fading, is called the “local mean” mean” and its power, often called the local average power. The measured mean value is log normally distributed distribut ed about the derived value with a standard deviation as shown in Figure 4-3 below.

Derived Mean

    y       t       i       l       i       b      a       b      o      r       P

Measured Mean

Standard Deviation ( )

SS at RX antenna

Figure 4-3 Log Normal Fading 

Therefore, this slow fading is called “log-normal fading” fading”. If we drive through a flat desert without any obstructions, the signal varies slowly with distance. However, in normal cases the signal path is obstructed. Obstructions near the mobile (for example, buildings, bridges, and trees) cause a rapid change in the local mean (in the range of five to fifty meters), whereas topographical topographical obstructions cause a slower signal variation (shadowing). Because log-normal fading reduces the average strength received, the total coverage from the transmitter is reduced. To combat this, a fading margin must be used.

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If outdoor base stations are used to provide indoor coverage building penetration loss must be take into consideration. consideration. Building penetration loss is defined as the difference between the average signal strength immediately outside the building and the average signal strength over the ground floor of the building. Typical values of the mean building penetration loss, BPL, are BPL, are given in Table 4-1 below. Environment

BPL [dB]

σ  LNF(o) [dB]

σ  LNF(i) [dB]

σ  LNF(o+i) [dB]

Dense urban

18

10

9

14

Urban

18

8

9

12

Suburban

12

6

8

10

Table 4-1 Building penetration loss 

The building penetration loss for different buildings is also lognormally distributed with a standard deviation of σ BP. BP. Variations of the loss over the ground floor could be described by a stochastic variable, which is log-normally distributed with a zero mean value and a standard deviation of σ floor  floor . Here σ BPL BPL and σ floor  floor  are lumped together by adding the two as if they were standard deviations in two independent log-normally distributed processes. The resulting standard deviation, σ indoor  indoor or σ LNF(i) t he sum of the LNF(i), could be calculated as the square root of the squares. Typical values of σ LNF(i) LNF(i) are presented in Table 4-1. The total log-normal fading is composed of both the outdoor lognormal fading, σ LNF(o) LNF(o),and the indoor log-normal fading σ LNF(i) LNF(i). The total standard deviation of the log-normal fading is given by the square sum: σ  LNF ( o +i )

=

σ  LNF ( o )

2

+ σ 

2

 LNF ( i )

Values of σ LNF(o+i) LNF(o+i) are presented in Table 4-1. These are the values that should be used in the link budgets when calculating the LNF marg  marg , required to achieve a certain probability of indoor coverage.

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This combining of standard deviations is illustrated in Figure 4-4 below.

σLNF(o+i) =

σLNF(o) 2+ σLNF(i) 2 σindoor or σLNF(i)

σLNF(o)

σBPL

σfloor Ground floor

Figure 4-4 Log-normal fading margins for indoor coverage 

Note that the characteristics of different urban, suburban etc. environments environments can differ significantly throughout the world. Thus the values in Table 4-1 must be treated with care. They should be considered as a reasonable approximation when no other information is obtainable. Rural areas are not considered in Table 4-1 since indoor coverage is not usually calculated for them. Once the standard deviation has been established the required LNF margin is determined from the required probability of coverage.

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In Figure 4-5 below it can be seen that a LNF margin of 4.1dB would be required to produce a 95 % probability of coverage if all users were outdoor outdoor in an urban environment. This increases to 7.5 dB if the same probability of coverage is required indoors.

Indoor Urban

95% probability of  coverage

Outdoor Urban

LNF=4.1 dB

Environment

BPL  [dB]

σ  LNF(o)  [dB]

σ  LNF(i) [dB]

Dense urba n

18

10

9

σ  LNF(o+i) [dB]

14

Ur ban

18

8

9

12

Suburb an

12

6

8

10

LNF=7.5 dB

Figure 4-5 LNF margins for urban environment 

A complete set of LNF margins for 3 sector sites is shown in Table 4-2 below.

Table 4-2 LNF marg  marg  for 3 sector sites 

The log-normal fading margins presented above reflect the case where the UE can make a handover to other cells when experiencing poor coverage. If handover is allowed, the log-normal fading margins can be reduced as compared to the single cell case. This reduction is referred to as handover gain and is included in the values for log-normal fading margins.

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POWER CONTROL MARGIN (PC MARG   )  MARG  In a WCDMA W CDMA system fast power control (1500 Hz) is employed. For slowly moving UEs the power control has the ability to compensate for the fast fading, thus reducing the Eb /No. However, due to the characteristics of the fast fading, more power will be required in the fading dips than t han the corresponding reduction in the fading tops. The result is that each UE (BS) has to t o increase its average power in order to combat fast fading. This effect is called TX increase. A sensitivity sensitivity degradation for UEs located at cell borders also appears, since the UE power control at cell borders no longer can fully compensate for fading f ading dips. To cater for the combined effect of TX increase and the sensitivity sensitivity degradation at cell borders a power control margin PC marg  marg  of typically 2 dB is used in the link budget. Note that this value is channel-model channel-mode l dependent. PCmarg for the various channel channel models is shown in Table 4-3 below.

Table 4-3 Power Control Margin (PC marg   ) marg 

The following losses must be considered for coverage calculations:

•

Body Loss (BL)

•

Car Penetration Loss (CPL)

•

Building Penetration Loss(BPL)

•

Feeder and Jumper losses (LF+J)

If an Antenna System Controller (ASC) is fitted at the base station, losses associated with the antenna feeder and jumper cables (LF+J) will be overcome overcome for the uplink. But they must be included included in downlink calculations calculations along with the insertion loss of the ASC (LASC).

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BODY LOSS (BL)  The human body has several negative effects on the UE performance. For example, the head absorbs energy, and the antenna efficiency of some UEs can be reduced. To cater for these effects a margin for body loss has to be included in the link budget. The body loss margin recommended by ETSI is 3 dB for 1900 MHz. Generally, body loss is not applied to data services since the users will most likely not have the terminal at their ear.

CAR PENETRATION LOSS (CPL)  When a UE is placed in a car without an external antenna, an extra margin has to be added in order to cope with the penetration loss to reach inside the car. This extra margin is approximately 6 dB. The recommended values for body and car losses are shown in Table 4-4 below.

Table 4-4 Body and Car penetration losses 

ANTENNA SYSTEM CONTROLLER (ASC) INSERTION LOSS (LASE  )  The ASC will add a propagation loss to the RBS downlink.

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FEEDER AND JUMPER LOSSES (LF+J  )  Feeder and jumper losses is the combined loss associated with the feeder and jumper cable, as below: Lf+J = Feeder attenuation + jumper attenuation Typical feeder attenuations are shown in Table 4-5 below.

Table 4-5 Typical Feeder Attenuation 

The jumper loss can vary depending on the length but typical values are in the order of 1dB.

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RBS SENSITIVITY (RBS SENS   )  SENS  The sensitivity of the RBS is the minimum signal level it needs to receive to decode the channel.

γ 

It is the C/I for the service ( ) added to the thermal noise (N) and the noise figure of the receiver (noise introduced by the RBS) as shown below: Minimum RX signal (RBSsens)= Noise + Nf +

γ 

In other words RBSsens is C/I dB above (Noise+Nf) as illustrated in Figure 4-6 below. RBSsens

C/I Noise +Nf

Figure 4-6 RBS Sensitivity 

The level of noise for a particular bandwidth and temperature can be calculated using the formula below. Noise = KTB W/Hz K is Boltzmann’ Boltzmann’s constant = 1.38 X 10-23 J/K T is the absolute temperature in Kelvin = 290 (17 o C) B is the bandwidth over which the noise is measured.

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If these are expressed as log values: Noise = KT KT + 10log(B) = Thermal noise noise (Nt) + 10 log (B) Therefore: RBSsens = Nt + 10log(B) + Nf +

γ 

γ 

However Eb/No =  +  + 10 log (B/Rinfo)

γ 

=  +  + 10 log (B) - 10 log (Rinfo) To solve for

γ 

γ 

=>  =  = Eb/No - 10 log (B) + 10 log (Rinfo)

γ 

If  is  is substituted into the equation for RBSsens it becomes: RBSsens = Nt + 10log(B) + Nf+ Eb/No - 10 log (B) + 10 log (Rinfo) The negative 10 log (B) will cancel out the positive one leaving equation 17 below.

RBSsens = Nt + Nf + 10 log (R info) +E +Eb/No dBm Equation 17 RBS Sensitivity equation 

where N t t is the thermal noise power density = -174 dBm/Hz   N f f is the noise figure = 3 dB with ASC, 4 dB without ASC   R user  user  is the total RAB bit rate in bps, i.e. user rate + 3.4 kbps signaling E b  b /N    o  o  is the energy per bit to noise ratio for the service.

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RBS Sensitivity Examples What is the sensitivity of an RBS with ASC for the services shown in Table 4-6 below?

Speech RBS sensitivity in dBm 64 kbps PS RBS sensitivity in dBm Table 4-6 Example RBS Sensitivities 

Nt = 10 log (KT) dBW/Hz K= Boltzman’ Boltzman’s constant 1.38 x 10-23 J/K T = Standard noise temperature = 290 o K => Nt = 10 log (KT/10-3) dBm/Hz = 10 log(1.38 x 10-23 X 290/10-3) = -174 dBm/Hz RBSsens = Nt + Nf + 10 log (Rinfo) +Eb /No dBm = -174 + 3 + 10log (Rinfo) +Eb /No dBm = -171 + 10log (Rinfo) +Eb /No dBm

For speech Rinfo = 12.2 kbps + 3.4 kbps = 15.6 kbps = 15600 bps RBSsens = -171 + 10log (15600) +Eb /No dBm = -171 + 41.9 +Eb /No = -129.1 +Eb /No

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When Eb /No = 4.9 dB RBSsens = -129.1 + 4.9 = -124.2 dBm When Eb /No = 6.4 dB RBSsens = -129.1 + 6.4 = ……… ……….. dBm

For 64kbps PS Rinfo = 64 kbps + 3.4 kbps = ….kbps = …… …….. .. bps RBSsens = -171 + 10log (……… (………..) ..) +Eb /No dBm = -171 + …… …….. +Eb /No = ……… ……….. .. +Eb /No When Eb /No = 3.2 dB RBSsens = ……… ……….. + 3.2 = …… …….... .... dBm When Eb /No = 4.5 dB RBSsens = …… ……..… + 4.5 = ……… ……….. dBm

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UPLINK LOAD  As users are connected to the cell the overall uplink noise will rise. This means that the sensitivity of the RBS will increase with also increase. As shown in Figure Figure 4-7 below the sensitivity of a loaded loaded RBS is the unloaded sensitivity plus the uplink noise rise (I UL) RBS RB Ssens (loaded) = RBSsens(unloaded) + I Ul Noise rise (I ul) RBS RB Ssens(unloaded) = N t + 10log (Bw) + Nf  +C/I

C/I Noise rise (Iul) Nt + 10log (Bw) + Nf

Figure 4-7 Sensitivity of loaded RBS 

Uplink noise rise can be derived from equation 18 below.

IUL = 10log

1 1-Q

dB

Equation 18 Uplink Noise Rise (I UL UL )

Where ‘Q ’ is the Uplink load in the cell (0 to 1)

Uplink Load Example How much will the uplink noise rise when a cell is becomes 50% loaded? Iul = 10 log (1/1-0.5) = ……… ………dB dB

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LINK BUDGET CALCULA C ALCULATION TION FOR UPLINK The signal level at the RBS receiver (SSRBS) will be the output power of the UE (PUE) minus any any losses plus plus any gains. gains. These losses and gains are shown in Figure 4-8 below.

Gant

RBS

SSRBS

Lf+j

Lpath PUE

Figure 4-8 Uplink link budget 

The losses are: Lpath is the path loss Lf+J = Losses in feeder and jumper The only gain is this example is that of the RBS antenna as the UE is assumed to have no antenna gain. This is expressed in equation 19 below.

SS RBS  = P UE – Lpath +G ant –Lf+j Equation 19 Signal strength at RBS 

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MAXIMUM PATH LOSS (LPATHMAX  )  The ideal uplink budget would be where the signal level at the RBS (SSRBS) is equal or greater than the RBS Sensitivity (RBSsens). In practice the loaded sensitivity should be used and the previous margins and losses must be included in the link budget calculations. This means that the SSRBS can be expressed as: SSRBS = RBSsens(loaded) + losses + margins  If the expression for SSRBS is substituted into this formula it becomes: PUE –  L  Lpath +Gant – Lf+j = RBSsens(loaded) + losses + margins  Since RBSsens(loaded) = RBSsens + IUL this formula becomes: PUE –  L  Lpath +Gant – Lf+j = RBSsens+ IUL+ losses + margins  Since Losses Since Losses = BL + CPL + BPL and margins = LNFmarg + PCmarg the formula can be written as: PUE –  L  Lpath +Gant – Lf+j = RBSsens + IUL + BL + CPL + BPL + LNFmarg + PCmarg If this equation is solved for ‘Lpath’ then the maximum path loss allowed for the cell (Lpathmax) is given by equation 20 below. Lpathmax  = PUE – RBSsens – IUL – LNFmarg – PCmarg – BL – CPL – BPL +Gant – Lf+j Equation 20 Maximum path loss (Lpathmax   )

where: Lpath is the path loss (on the t he uplink) [dB]. P UE  UE  is the maximum UE output power (= 21 or 24) [dBm]. RBS sens  sensitivity. [dBm]. sens  is the RBS sensitivity. LNF marg  fading margin [dB]. marg  is the log-normal fading

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I UL UL is the noise rise [dB]. PCmarg  is the power control margin [dB]. BL is BL is the body loss (= 0 or 3) [dB]. CPL is the car penetration loss (= 6) [dB]. [ dB]. BPL is the building penetration loss [dB]. G ant  ant  is the sum of the RBS and UE antenna gains [dBi]. Lf+j  is the loss in feeders and jumpers [dB]. This formula may be used to calculate the various maximum path losses for each service, as shown in Figure 4-9 below. PS

Lpathmax

TU, 50 km/h

PS

Lpathmax

TU, 3 km/h

Lpathmax  TU,  TU, 50 km/h

Lpathmax  TU,  TU, 3 km/h

Figure 4-9 Maximum uplink path losses 

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WCDMA CELL RANGE  When roughly estimating the size of macro cells, without taking into account specific terrain features in the area, the OkumuraHata propagation formula can be solved for R to give equation 21 below. R pathmax = 10α, where α = [Lpathmax - A + 13.82logHb + a(Hm)]/[44.9 - 6.55logH b]

Equation 21 Maximum range using Okumura-Hata formula 

where A = 155.1 for urban areas A = 147.9 for suburban and semi-open areas A = 135.8 for rural areas A = 125.4 for open areas Hb = base station antenna height [m] Hm = UE antenna height [m] R = distance from transmitter [km] a(Hm) = 3.2(Log(11.75*H 3.2(Log(11.75*Hm))2- 4.97 a(1.5) = 0 It must be emphasized that the Okumura-Hata formula only can be used for rough estimates. For more precise numbers, networkplanning tools should be used.

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For small cells in an urban environment the cell range is typically less than 1 km and in that t hat case the Okumura-Hata formula is not valid. The COST 231-Walfish-Ikegami model, gives a better approximation approximation for the t he cell radius in urban environments. environments. The COST 231-Walfish-Ikegami model formula is solved for R to give equation 22 below. Rpathmax = 10α, where α = [Lpath – 155.3 + 18log(Hb 1 8log(Hb – 17)]/38 Equation 22 Maximum range using COST 231-Walfish-Ikegami 

Note: The expressions above have been adapted to 2.05 GHz.

SITE COVERAGE AREA This range may now be used to calculate the coverage area of the site using equation 23, 24 or 25 for omni, three-sector and six sector sites respectively as illustrated in Figure 4-10 below.

 Area =

3 2

2 3 R

 Area =

9 8

 R

SitetoSite = 3 R Equati on 23

2 3 R

 Area =

3 2

 R

 R

SitetoSite =

3 2

R

Equati on 24

2 3 R

SitetoSite = 3 R Equati on 25

Figure 4-10 Relationships between coverage area and cell range 

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 Example Uplink calculation Complete Table 4-7 below for a three sector urban site to deliver 95 % probability of coverage to AMR 12.2 kbps to TU 3 km UEs at 50 % load. PUE 

21

 RB  RBS sens Outdoor LNF marg marg

4.1

PC marg

0.7

 I UL  BL  BL

3

Gant 

17.5

 L f+j

0

 L path  pathm max (outdoor) CPL

6

 L path  pathm max (in-car)  BP  BPL

18

 Ind  Indoor LNF marg

7.5

 L path  pathm max (indoor)

Table 4-7 Example UL Calculation 

NOTE: the outdoor service is assumed to be pedestrians as opposed to users in vehicles.

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4. WCDMA Coverage

DOWNLINK DIMENSIONING For the downlink it is not as easy to separate the coverage and capacity in the way that is done for the uplink. The main difference as compared to the uplink is that the UEs in the downlink share one common power source. Thus the cell range is not dependent only on how many UEs there are in the cell but also on the geographical geographical distribution of the UEs. Despite orthogonal codes, the downlink channels can not be perfectly separated due to multipath propagation. This means that a fraction of the BS power will be experienced as interference. Also, the downlink interference, caused by neighboring base stations transmitting channels that are not orthogonal to the serving base station, is user equipment position dependent. dependent. The final equations are quite complex and difficult to use. In order to facilitate the dimensioning dimensioning process, curves have been generated based on the equations. The curves display the cell load (M/M  (M/M pole  range. The curve for an urban urban 3pole ) versus the cell range. sector site is shown in Figure 4-11 below.

Figure 4-11 DL capacity verses Cell Range 

Typical parameter values have been used and 20% of the power has been allocated to control channels. A homogenous user

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WCDMA Radio Network Design

distribution has been assumed. To account for non-homogenous distributions and log-normal fading a 5 W headroom has been used. Thus the curves are based on a total power Ptot,s of 15 W instead of 20 W. This roughly corresponds to 95% coverage probability.

DOWNLINK LINK BUDGET  Before we can use this t his curve we must calculate the downlink margin DLmarg with equation 26 below.

DLmarg = BL + CPL + BPL +∆Gant ant + Lf+j f+j + LASC +∆Nf + ∆A0 Equation 26 Downlink Margin (DLmarg  )

BL is BL is the body loss. CPL is the car penetration loss. Since this is an urban area car loss will not be considered. BPL is the building penetration loss. ∆G ant  ant  is

the difference in antenna gain compared compared to the value used in the curves. 17.5 –  G  Gant ∆Gant= 17.5 –  Lf+J  is the loss in feeders and jumpers. ∆N f f is  

the difference in UE noise figure compared to the value used in the curves ∆Nf = Nf  – 7 LASC  is the insertion loss of the ASC (if used). ∆A0 is

the difference of the distance independent term, in Okumura Hata, compared to the value used in the curves  – A0curves , where A0  = A –  13.82  13.82 logH  logH b  A0curves  is ∆A0  = A0  – A b and   134.68 or approx. 134.7

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4. WCDMA Coverage

Example Downlink Calculation What load could a 40m, 3-sector Urban Cell cope with at a range of 1.5 km? Firstly the DL margin must be calculated:

DLmarg = BL + CPL + BPL +∆Gant ant + Lf+j f+j + LASC +∆Nf + ∆A0 BL= BL= 3 dB. CPL = CPL = 0 dB  BPL = BPL = 18 dB  ∆G ant  ant  =

17.5 –  17.5 –  G  Gant      ant = 0 dB

Lf+J  5 dB (typical value) ∆N f f =  

Nf       f= 0 dB

LASC =0.4 ∆A0 =

A0 - 134.7 but A0 = 155.1 –  155.1 –  13.82  13.82 log(40)= 133  0 = 133 - 134.7 = -1.7 dB

Dlmarg = 3 + 0 + 18 + 0 + 5 + 0 + 0.4 -1.7 = …… …….. dB

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WCDMA Radio Network Design

Where a line drawn through 1.5 km interecets the closest DLmarg plot to …… …….. .. will give the supported load of the cell as shown in Figure 4-12 below  belo w.

Figure 4-12 Example DL Calculation 

The maximum load supported by the cell is …… …….. .. %.

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