Umts Link Budgets

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UMTS link budgetsUMTS link budgets

UMTS link budgets


ContentsContents• What is a link budget?• Link budget parameters.• Uplink link budget.• Downlink link budget.• Cell ranges.• Cell loading.

UMTS link budgets


The Link Budget ParametersThe Link Budget Parameters

•Information Rate •Interference margin (Intercell & Intracell)•Fast Fading Margin•Soft Handover Gain•Required Eb/No•Body Loss•Penetration Loss•Mobile antenna Gain•Base station antenna gain•Shadow Fading Margin

UMTS link budgets


Information RateInformation Rate

This is the bit rate that the user service requires.

Currently in UMTS the following non packet options are supported: 4.75,5.15,5.9,6.7,7.4,7.95,10.2,12.2kbit/s (AMR Voice Codec), 32, 64, 144, 384 kbits/s LCD

UMTS link budgets


Interference marginInterference margin

The interference margin is used to account for the increase in the interference levels within the cell due to other users.

It introduces in the link a budget a way for accounting for the loading of the cell.

The more loading is allowed the larger a margin is needed.

Typical values for the interference margin are between 1-3dBcorresponding to 20%-50% loading.

UMTS link budgets


Fast Fading marginFast Fading margin

The Fast Fading margin is included to account for the additional headroom needed in the mobile station transmitionpower to maintain adequate power.

This is a consequence of the fast power control utilised in UMTS

Typical values are between 2-5dB

UMTS link budgets


Soft Handover gainSoft Handover gain

Soft handover gain accounts for the diversity gain achieved during soft handover conditions.

The soft handover gain is extracted by the receiver being able to compensate for both slow and fast fading since it has information arriving from almost uncorrelated paths.

It is highly sensitive to channel conditions and number of link available.

Typical values are usually assumed to be between 2-4dB

UMTS link budgets


Required Required EbEb/No/No

This the required Eb/No needed by the user service to maintain error free links.

It can be affected by parameters such as-channel type -mobile speed-QoS-receiver implementation

UMTS link budgets


Body LossBody Loss

The body loss introduces in the link budget the effect of the human being handling the terminal.

It is a variable parameter that in general depend on the operational conditions the environment and the human being. Usually an average value is introduced in the link budget.

Typical values are about 3dB

Note that in UMTS it is expected that for a lot of non voice The use of the terminal will not result in losses due to the body.

UMTS link budgets


Penetration LossPenetration Loss

Penetration Loss accounts for the environment the mobile operates in.

Typical examples include:•Indoor. Typical generalised value of about 15dB•In car. Typical generalised value of about 8dB

Note that the actual value between different environments can vary significantly. Ideally measurements for the local conditions are needed

UMTS link budgets


Antenna GainAntenna Gain

Accounts for the gain at the antennas of the mobile terminal and Base Station

Typical values for the Mobile station are 0dBi although it is expected that some data terminal will have antennas giving slightly higher gain ~2dBi.

Base station antennas gains are dependant on configuration but Typically are similar to DCS 1800 values.

UMTS link budgets


Shadow fading MarginShadow fading Margin

The shadow fading margin introduces a way to include in the link budget the effect of reliability required.

It is dependant on the environment surrounding the base station and mobiles.

UMTS link budgets


• Processing gain Gp is the ratio of transmission bandwidth Bt to information bandwidth Bi.

• Gp = Bt

• It represents the ability of the receiver to disregard unwanted spread signals.

Processing gainProcessing gain

Bi

__

Channel

Spreading Code Signal

Rx Signal (= Tx Signal + Noise)

f

P

P

f

UMTS link budgets


Receiver NoiseReceiver Noise• The receiver noise power is mostly thermal noise which is increased by

the receiver noise figure.• Thermal noise can only be reduced by cooling the receiver.• The only way of reducing the level of noise is by selecting a receiver

with a low noise figure.Receiver noise power = Receiver noise density + Information rate

[dbm/Hz] [db Hz]

Receiver noise density = Thermal noise density + Receiver noise figure[dbm/Hz] [dbm/Hz] [db]

Information Rate = 10 log (Chip Rate)

UMTS link budgets


Uplink BudgetUplink Budget

Mobile Terminal Side Base Station Side

RequiredEb/No

Losses

Gains

Losses

Gains

TransmittedPower

ReceiverSensitivityEIRP Maximum

acceptableUplink

Path Loss

UMTS link budgets


Downlink BudgetDownlink BudgetMobile Terminal SideBase Station Side

RequiredEb/No

Losses

Gains

ReceiverSensitivity

Maximumacceptable

UplinkPath Loss

EnvironmentCorrection

Reliabilitymargin

UplinkPath loss

LossesGains

Output Powerper link

EIRP

LoadingFactor

UMTS link budgets


An Example of the Uplink BudgetAn Example of the Uplink BudgetService type RT 144kbit/s, 3km/h

Mobile speed km/h 3Frequency MHz 2000 FChip Rate MHz 3.84 WData Rate kb/s 144 R

Uplink link budget

Max Load 50 %Transmitter (MS) BSMax transmitted Power dBm 24 aAntenna Gain dBi 0 bBody Loss dB 0 cCable Loss 0 clEIRP dB 24 d=a+b-c-cl

Receiver (BS) MSThermal Noise density dBm/Hz -174 eReceiver NF dB 5 fReceiver Noise density dBm/Hz -169 g=e+fReceiver Noise Power (Pn) dBm -103.1566878 h=g+10*log(W*10^6)Interference Margin (Ir) dB 3.010299957 ITotal interference (Io) dBm -103.1566878 j=10*LOG(10^((i+h)/10)-10^(h/10))Total interfernce + noise (Io+Pn) dBm -100.1463878 k=10*log(10^(h/10)+10^(j/10))

Required Eb/No dB 1.5 lMDC Gain dB 0 IaProcessing Gain 14.25968732 m=10*LOG(W/R)Receiver sensitivity dBm -112.9060751 n=k-m+l-Ia

Antenna Gain dBi 18 oCable Loss dB 2 pBody Loss pblFast Fading margin (TPC) dB 4 q

Max Path loss dB 148.9060751 r=d-n+o-p-q

UMTS link budgets


An Example of the Downlink BudgetAn Example of the Downlink BudgetDownlink link budget

Max Load 50 %Transmitter (MS)Max transmitted Power dBm 8.564573042 dBm/channel a=d-b+clAntenna Gain dBi 18 bBody Loss dB cCable Loss 2 clEIRP dB 24.56457304 d=r+n-o+p+q+pbl

Receiver (BS)Thermal Noise density dBm/Hz -174 eReceiver NF dB 8 fReceiver Noise density dBm/Hz -166 g=e+fReceiver Noise Power (Pn) dBm -100.1566878 h=g+10*log(W*10^6Interference Margin (Ir) dB 3.010299957 ITotal interference (Io) dBm -100.1566878 j=10*LOG(10^((i+h)/Total interfernce + noise (Io+Pn) dBm -97.1463878 k=10*log(10^(h/10)+

Required Eb/No dB 5.5 lMDC Gain dB 1.2 IaProcessing Gain 14.25968732 m=10*LOG(W/R)Receiver sensitivity dBm -107.1060751 n=k-m+l-Ia

Antenna Gain dBi 0 oCable Loss dB 0 pBody Loss 0 pblFast Fading margin (TPC) dB 0 q

Path loss dB 131.6706482

UMTS link budgets


An Example of the Range An Example of the Range DimensionerDimensionerCell DimensioningPath loss dB 148.9060751

standard deviation 12Added In-car loss dB 0Added In building Loss dB 15Standard Deviation (Sw) in dB 12path loss exponent (n) 3.5

Area Location probability 80.00000183Log Normal fading margin dB 4.235426958Soft Handover Gain dB 2

Allowed Path loss 131.6706482

Frequency MHz 2000Base Station Antenna Height (Hb m 30Mobile Antenna Height (Hm) m 1.5Road Width (Rw) m 20Road orientation (ro) deg 90Building separation (Bs) m 50Building Height (BH) m 25

Clutter Correction loss (cm) 4Mobile antenna height correction (a(hm)) 0

0.516047894range in (Okumura-Hata) km 0.516016893

Range (Walfish-Ikegami) km 0.325279716

UMTS link budgets


Typical Ranges in UMTSTypical Ranges in UMTS

DenseUrban

Urban SubUrban Rural Open

12 kbps Speech 0.28 0.39 0.99 1.28 2.1664 kbps RT data 0.25 0.34 0.85 1.11 1.87144 kbps NRT data 0.29 0.40 1.00 1.30 2.19384 kbps NRT data 0.23 0.31 0.78 1.01 1.71

DenseUrban

Urban SubUrban Rural Open

12 kbps Speech 1.40 1.82 3.07 3.98 5.1764 kbps RT data 1.21 1.57 2.66 3.45 4.48144 kbps NRT data 1.42 1.84 3.10 4.03 5.24384 kbps NRT data 1.11 1.44 2.43 3.15 4.10

Indoor with 95% probability

Outdoor with 95% probability

UMTS link budgets


Uplink loadingUplink loading

The loading factor is defined as

∑∑∑∑====ηηηηtotal

rxdUL I

P

Where Prxd is the received power for that link

Itotal is the total interference in the cell

It can be linked to the Noise Rise as

UL11NoiseRiseηηηη−−−−

====

UMTS link budgets


Uplink loadingUplink loading

The loading factor can also be linked to the user generated traffic as:

(((( ))))(((( ))))

∑∑∑∑====

υυυυ⋅⋅⋅⋅⋅⋅⋅⋅++++

++++====ηηηηN

1j

jjj0b

UL

RNEW1

1i1

Where Rj is the bit rate of the j-th link in the cell

υj is the user activity factor

i is the other to own cell interference ratio

Eb/N0 is the target for the j-th link in the cell

W is the chip rate

UMTS link budgets


Uplink loading and RangeUplink loading and Range

0

0.5

1

1.5

2

2.5

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Cell Loading

Ran

ge (k

m)

Voice 12.2 kbit/s, 3km/h

Effect of loading on cell range

UMTS link budgets


Downlink loadingDownlink loading

In the Downlink the loading factor can be expressed as

Where αj is the orthogonality factor in the downlink

Rj is the bit rate of the j-th link in the cell

υj is the user activity factor

i is the other to own cell interference ratio

Eb/N0 is the target for the j-th link in the cell

W is the chip rate

(((( ))))(((( ))))∑∑∑∑

====

++++αααα−−−−

υυυυ⋅⋅⋅⋅⋅⋅⋅⋅++++

====ηηηηN

1jjj

jjj0b

DL i1

RNEW1

1

UMTS link budgets


Base Station Transmitted Power DimensioningBase Station Transmitted Power Dimensioning

The limiting factor in the Downlink is the maximum power that the amplifier can provide.

An estimate of the Base Transmitted power can be determined using: ( )

( )DL

N

j j

jobjrf

BStotal

RWNE

LWNP

η

υ

−

⋅⋅⋅=

∑=

11

_

Where Nrf is the noise spectral density at the receiver

NFNrf +−= 2.108

UMTS link budgets


Coverage Coverage vs vs Capacity relationCapacity relation

145

150

155

160

0 5 10 15 20 25 30 35 40 45 50UL Load

Path

loss

NRT Data 144k UL PathlossNRT Data 384k UL PathlossDL Pathloss, low asymmetryDL Pathloss, medium asymmetryDL Pathloss, high asymmetry

Capacity is uplink limited

Capacity is Downlink limited

UMTS link budgets

Umts Link Budgets

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