UMTS Linkbudget and Capacity Analysis.pdf

8/12/2019 UMTS Linkbudget and Capacity Analysis.pdf

1/26

UMTS Link Budgetand Capacity Analysis

Dr, Hatem MOKHTARISenior RF Systems Expert

(2G/3G/4G/WIMAX)


2/26

Link Budgets

A Link budget analysis should include

Uplink service link budget

Downlink service link budget

CPICH link budget

Link budgets should be completed for each serviceand each environment type

Each link budget generates a maximum allowedpath loss result

The smallest result defines the cell range once anappropriate path loss model has been applied


3/26

Interference Floor (dBm)

Eb/No

(dB)

Processi

ng Gain

(dB)C/I

(dB)

Sensitivity

(dBm)

Link Budget Concepts

C/I Requirement = Eb/No Requirement Processing Gain

Sensitivity = Interference Floor + C/I Requirement

Interference Floor = kTB + Noise Figure + Interference Margin

Interference Margin = -10 LOG(1 Cell Load)

Thermal Noise

(dBm)

Interferenc

e margin(dB)


4/26

Service Type Speech CS Data PS Data

Uplink bit rate 12.2 64 64 kbps

Maximum transmit power 21.0 21.0 21.0 dBm

Antenna gain 0.0 0.0 2.0 dBi

Body loss 3.0 0.0 0.0 dB

Transmit EIRP 18.0 21.0 23.0 dBm

Processing gain 25.0 17.8 17.8 dB

Eb/No Requirement 4.4 2.0 2.0 dB

Target loading 50 50 50 %

Rise over thermal noise 3.0 3.0 3.0 dB

Thermal noise density -174.0 -174.0 -174.0 dBm/Hz

Receiver noise figure 3.0 3.0 3.0 dB

Interference floor -168.0 -168.0 -168.0 dBm/Hz

Receiver sensitivity -122.8 -118.0 -118.0 dBm

RX antenna gain 18.5 18.5 18.5 dBi

Cable loss 0.0 0.0 0.0 dB

Fast fading margin 3.0 3.0 3.0 dB

Soft handover gain 2.0 2.0 2.0 dB

Building penetration loss 12 12 12 dB

Slow fade margin 10 10 10 dB

Isotropic power required -118.3 -113.5 -113.5 dBm

Allowed propagation loss 136.3 134.5 136.5 dB

Maximum uplink bit rate is 64 kbps

Separate CS and PS link budgets

UE antenna gain and body lossassumptions can be service specific

Eb/No includes benefit of uplinkreceive diversity

Target loading is environment

dependent such that high trafficareas have greater load and anincreased site density

MHA is assumed to compensate forcable loss in the uplink direction

Fast fade margin is a function of UE

speed

Building penetration loss isevironment dependent

Example Uplink Service Link Budgets


5/26

Service coverage isdownlink limited

Maximum downlinktransmit powerscomputed by RNC RRM

Downlink Eb/No excludereceive diversity

MDC gain represents asoft handover gain thatreduces the Eb/No

Downlink load typicallygreater than uplink load

Soft handover gain

represents a softhandover gain thatreduces the transmitpower requirement

Service Type Speech CS Data PS Data PS Data PS Data

Downlink bit rate 12.2 64 64 128 384 kbps

Maximum transmit power 32.2 35.2 35.2 38.0 40.0 dBmAntenna gain 18.0 18.0 18.0 18.0 18.0 dBi

Cable loss 2.0 2.0 2.0 2.0 2.0 dB

Transmit EIRP 48.2 51.2 51.2 54.0 56.0 dBm

Processing gain 25.0 1 7.8 17.8 14.3 10 .0 dB

Required Eb/N0 7.9 5.0 5.0 4.7 4.8 dB

MDC Gain 1.2 1.2 1.2 1.2 1.2 %

Loading 80 80 80 80 80 %

Rise over thermal noise 7.0 7.0 7.0 7.0 7.0 dB

Thermal noise density -174.0 -174.0 -174.0 -174.0 -174.0 dBm/Hz

Receiver noise figure 8.0 8.0 8.0 8.0 8.0 dB

Interference floor -159.0 -159.0 -159.0 -159.0 -159.0 dBm/Hz

Receiver sensitivity -110.3 -106.0 -106.0 -102.8 -98.4 dBm

RX antenna gain 0.0 0.0 2.0 2.0 2.0 dBi

Body loss 3.0 0.0 0.0 0.0 0.0 dB

Fast fading margin 0.0 0.0 0.0 0.0 0.0 dB

Soft handover gain 2.0 2.0 2.0 2.0 2.0 dB

Building Penetration Loss 12 12 12 12 12 dB

Slow Fade Margin 10 10 10 10 10 dB

Isotropic power required -87.3 -86.0 -88.0 -84.8 -80.4 dBm

Allowed propagation loss 135.5 137.2 139.2 138.8 136.4 dB

Example Downlink Service Link Budgets


6/26

CPICH transmit power typically 10 % of thetotal transmit power capability

CPICH Ec/Io requirement may be planned toa more stringent value, e.g. 12 dB

No soft handover in CPICH link budget

Service Type CPICH

Transmit power 33.0 dBm

Antenna gain 18.0 dBi

Cable loss 2.0 dB

Transmit EIRP 49.0 dBm

Ec/Io Requirement -15.0 dB

Loading 80 %

Rise over thermal noise 7.0 dB

Thermal noise density -174.0 dBm/Hz

Receiver noise figure 8.0 dBInterference floor -159.0 dBm/Hz

Receiver sensitivity -108.2 dBm

RX antenna gain 0.0 dBi

Body loss 3.0 dB

Fast fading margin 0.0 dB

Building Penetration Loss 12 dB

Slow Fade Margin 10 dB

Isotropic power required -83.2 dBm

Allowed propagation loss 132.2 dB

Example Downlink CPICH Link Budget


7/26

In this example, overall coverage is CPICH limited and the resultant maximumallowed path loss is 132.2 dB

This figure can be used to trigger inter-system handovers, i.e. when the UEmeasures a CPICH RSCP which corresponds to a path loss of 132.2 dB

RSCP which corresponds to 132.2 dB:

33 dBm 2 dB +18 dBi 132.2 dB = -83.2 dBm

Slow fade margin and building penetration loss should be removed

because UE incurs these prior to making the measurement, thus

-83.2 dBm 10 dB 12 dB = -105.2 dBm

Link Budget results can also be used in a planning tool to define the downlinkcoverage thresholds, e.g. if planning tool is run with a downlink EIRP of 50 dBmthen the planning threshold = 50 dBm 132.2 dB = -82.2 dBm. The EIRP is

arbitrary and does not matter. Link budget results can also be used to define RF scanner drive test coverage

thresholds

Using Link Budget Results


8/26

The WCDMA radio environment has an impact upon:

Eb/No requirement Power control headroom

Diversity

Soft handover gains

Orthogonality

Inter-cell interference

Power control generated rise in inter-cell interference

Each impacts coverage and/or capacity

WCDMA Radio Environment


9/26

Eb/No Requirement (I)

Eb/No is the energy per L2 bit divided by the noise spectral density Eb/No impacts both coverage and capacity

Eb/No requirement is a function of

BLER requirement

bit rate

transmission time interval (interleaving depth)

channel coding

UE speed

power control step size and algorithm

propagation channel

receiver and transmitter implementation

Eb/No form part of the RNC data build


10/26

Eb/No Requirement (II)

RNC contains up to 15 sets of Eb/No tables. These tables can be

selected on a per cell basis using the WCEL parameter -EbNoSetIdentifier

Each set of tables contains:EbNoPlannedCSAMRULEbNoCSAMRclassAULEbNoCSAMRclassBULEbNoCSAMRclassCUL

EbNoPlannedDataULEbNoPlannedSLUL

EbNoCSspeechULmaxEbNoCSspeechULmin

EbNoDataULmaxEbNoDataULmin

EbNoSLULmaxEbNoSLULmin

EbNoPlannedCSAMRDLEbNoCSAMRclassADLEbNoCSAMRclassBDLEbNoCSAMRclassCDL

EbNoPlannedDataDLEbNoPlannedSLDL

Uplink figures used for:

Calculation of rate matchingAttributes

Calculation of initial target SIR

Evaluating capacity requests

Downlink figures used for:

Calculation of rate matchingattributes

Evaluating capacity requests

Calculation of maximumdownlink transmit power

RNC data build Eb/No do notinclude DPCCH overhead


11/26

Power Control Headroom (I)

Changeinpath

loss

Transmitp

ower

requirem

ent

Av. txpower

Max. txpower

Power control headroom is the transmit power margin required to

track fast fading (fast fading margin) Power control headroom impacts coverage

Power control headroom is a function of

UE speed

Propagation channel

Inner loop power control step size and algorithm


12/26

Power Control Headroom (II)

Transmitpower

require

ment

Av. txpower

Max. txpower

Power control headroom has greatest impact upon slow moving

UEs Channel coding performs best when bit errors are evenly

distributed throughout a block of data

Bit errors generally occur in bursts and deinterleaving isresponsible to re-distributing them

If fades are wide i.e. slow moving UE, then deinterleaving isless able to avoid consecutive bit errors (depends upon TTI)

Fast moving UE Slow moving UE

Transmitpower

require

ment

Av. txpower

Max. txpower

Narrow bursts oferrors

Wide bursts oferrors


13/26

Diversity

Time diversity is provided by interleaving over the Transmission Time

Interval (TTI) Effectiveness of interleaving depends upon the width of any bursts of bit

errors

Multi-path diversity is provided by the combination of delay spread

components within the rake receiver Delay spread has to be > 1 chip (path difference > 78 m) to be resolved

Space diversity can be introduced by using multiple antenna elements tocover the same coverage area

Space diversity may be used in the uplink (receive diversity) and/or downlink (transmit diversity)


14/26

Soft Handover Gains

Soft handover gain is another form of diversity gain

The greater the multi-path, time or space diversity already present, thesmaller the incremental soft handover gain

Soft handover gains appear at both the transmitter and receiver there arethree types of soft handover gain:

reduction in Eb/No (impacts capacity and coverage)

reduction in fast and slow fading margins (impacts coverage) reduction in the rise of intercell interference (impacts capacity)


15/26

Orthogonality

Orthogonality is a measure of how transparent one code channel is to

other code channels OSVF codes are completely orthogonal when time synchronised

OSVF codes are transmitted in a time synchronised fashion from the NodeB

Multi-path delay spread introduces non-synchronised components

Delay spread is small within an indoor environment relative to an outdoorenvironment resulting in a greater orthogonality

Orthogonality impacts downlink capacity

Scrambling codes are not orthogonal to one another i.e. inter-cell

interference does not benefit from orthogonality

Introducing a secondary scrambling code e.g. for capacity reasons, has an

impact upon orthogonality

Orthogonality forms part of the RNC data build


16/26

Intercell Interference Ratio

Some overlap between cells is essential to support soft handover and

provide contiguous coverage Excessive overlap results in a reduced system capacity in both the uplink

and downlink directions

Inter-cell interference ratio is defined as:

Intercell Interference Ratio=

IotherIown

Intercell interference ratio does not form part of the RNC data build


17/26

Rise in Uplink Intercell Interference Ratio

Uplink intercell interference ratio may be increased by power spikesreceived from UEs whose transmit power is being controlled by a

neighboring cell

Serving cell provides UE with inner loop power control commands tomaintain constant power at its receiver

Power received by neighboring cells is not constant and may be spikey

Power spikes cause an increase in the level of intercell interference

TPCcommand

s

Other cellinterferenc

e

Receivedpower(relativelystrong andconstant)

Neighborcell

Serving cell

Fading1

Fading2

Receivedpower(relativelyweak butspikey)


18/26

Node B Capacity

Node B capacity is defined by: Dedicated channel (DCH) capacity Random access channel (RACH) capacity Forward access channel (FACH) capacity Paging channel (PCH) capacity

The DCH capacity is typically assumed to be thebottleneck

The DCH capacity is determined by: WSP card configuration Radio network plan, e.g. intercell interference,

cell range Node B RF configuration, e.g. sectors, carriers

Channelisation code configuration

Capacity is often expressed in terms of kbps for aspecific traffic mix


19/26

Uplink Air-Interface Capacity

Uplink air-inteface capacity is defined by the maximum allowed increase inuplink interference

Uplink air-interface capacity can be estimated using the uplink loadequation

iaRW

NoE

j

jbNj

j

jUL *1/

/

1

ActivityFactor ChipRate BitRate

IntercellInterference Ratio

Rise in IntercellInterference Ratio

Eb/NoRequirement

Uplink Load

Number of connections can be computed for a specific uplink load

Result is sensitive to the Eb/No requirement


20/26

Downlink Air-Interface Capacity

Downlink air-inteface capacity is defined by the maximum downlink transmitpower capability

Downlink air-interface capacity can be estimated using a combination of thedownlink load equation and a downlink link budget calculation

Activity

Factor

Chip

Rate

Bit

Rate

Intercell

Interference Ratio

Rise in IntercellInterference Ratio

Eb/NoRequirementDownlink Load

Transmit power consumed by the common channels must be accounted for

The link budget calculation computes the transmit power requirement per UE

iRW

NoEOHSHO

j

jbNj

j

jDL *1/

/)_1(

1

Softhandover

overhead


21/26

Mast Head Amplifiers

Dedicatedantenna

system

Sharedfeeders

MHAs

Bias-Ts GSM WCDMA

Diplexors

DC line

Friis' equation used to evaluate the

composite receiver noise figure.

Benefit depends upon receiver feederlength

Receiver sensitivity improved byreduction in noise figure

Capacity affected by downlinkinsertion loss and greater isotropicpath loss

Dedicated Feeders Shared Feeders

Feeder

Loss

NF without

MHA

NF with

MHA

Benefit NF without

MHA

NF with

MHA

Benefit

1.0 dB 4.0 dB 2.6 dB 1.4 dB 4.6 dB 2.7 dB 1.9 dB

2.0 dB 5.0 dB 2.8 dB 2.2 dB 5.6 dB 2.9 dB 2.7 dB

3.0 dB 6.0 dB 3.0 dB 3.0 dB 6.6 dB 3.2 dB 3.4 dB

4.0 dB 7.0 dB 3.3 dB 3.7 dB 7.6 dB 3.5 dB 4.1 dB


22/26

Dual branch upl ink receive diversity generally included asstandard

Higher order receive diversity planned on a site by site basis

Direct impact is to decrease Eb/No requirement

0 200 400 600 800 1000

Mean Ptx = 4.4 dBm (2 Rx Div)

Mean Ptx = 1.57 dBm (4 RX Div)

Distance alongroute (m)

Mobile PTx (dBm)

-20

-10

0

10

20

30

Mobile transmissionpower is reducedon average 2.8 dB

Precise gain dependent uponthe radio channel, typically2.5dB

Able to simultaneouslyimprove both coverage andcapacity

Impact upon capacitydependent uponcapacity limitation - ULor DL

Coverage gain similarto that provided byMast Head Amplifiers

2 cross polarantennas insingle housing

2 spatiallyseparated cross

polar antennas

Higher Order Receive Diversity (UL SRC)


23/26

RF CarriersMajority of 3G operators have 2 or 3 FDD carriers assigned byregulator

Provides the simplest and most effective means of increasing systemcapacity

Coverage improves while cell loading is reduced - returns to normalonce the level of traffic increases such that cell load is equal tooriginal load

Node B transmit power capability is used most effic iently when spreadacross the maximum number of carriers i.e. 2 carriers each w ith 10Whas greater capacity than 1 carrier with 20W

Carrier increase can be done with only additional TRXs or addit ionalTRXs and WPAs

Doubling the number of carriers and doubling the number of WPAs

leads to at least twice the cell capacity - more than twice when RadioResource Management supports load balancing across carriers -trunking gain

PATRX

Tx

Rx Rx

PATRX

Tx

Rx Rx

TRX

Tx

Rx Rx

PATRX

Tx

Rx Rx

TRX

Tx

Rx Rx

PA

1 carriercapacity = x

2 carriercapacity =

2x

2 carriertypical capacity =

1.6x(scenario


24/26

Transmit Diversity (DL SRC)

Increases the downl ink system capacity by reducing the downlink Eb/Norequirement

Functionality is mandatory in the UE

PATRX

Tx

Rx Rx

Duplexor

PowerAmplifiers

Transceivers

PATRX

Tx

Rx Rx

Modified Vehicular A Pedestrian A

3 km/h 50 km/h 120 km/h 3 km/h

Open Loop Mode 1.0 dB 0.5 dB 0.5 dB 3.0 dB

Closed Loop Mode 1 1.5 dB 1.0 dB 0.0 dB 3.5 dB

Benefit is greatest when there is litt le multipath and litt le timediversity

Microcells may benefit f rom up to 70% capacity increase

Macrocells typically benefit f rom up to 30% capacity increase

Multi-carrier transmit diversity configurations may share PAmodules

Reduction in downlink Eb/No requirement


25/26

BTS Transmit Power Configuration

0

10

20

30

40

5060

70

80

140 145 150 155 160 165 170

Isotropic Path Loss (dB)NumberofSpeechU

sers

Base StationTransmit Power per

Cell per Carrier

37dBm (5W)40dBm (10W)

43dBm (20W)

46dBm (40W)

requirement dependent upon downl ink cell loading and cell l ink

budgetsmaller cells are less sensit ive to BTS transmit powerconfiguration range of typical BTS

transmit powerconfigurations

power used mostefficiently when sharedacross carriers


26/26

Sectorisation

65 antenna

33 antenna

Effective solution for increasing capacity for operators with limitedcarriers

Increased difficulty in managing soft handover and intercell isolation

Choice of antenna beamwidth impacts intercell isolation

Application

1 Sector Microcell or low capacity macrocell

2 Sector Sectorised microcell or macrocell providing roadside coverage

3 Sector Standard macrocell configuration providing medium capacity

4, 5 Sector Not commonly used but may be chosen to support a specific traffic scenario

6 Sector High capacity macrocell configuration

Typical AntennaBeamwidth and

Gain

Typical Inter-cellInterference Ratio

Typical SoftHandoverOverhead

1 Sector 65/ 12.0dBi 25% 20%Microcell

2 Sector 65/ 12.0dBi Scenario dependent Scenario dependent1 Sector 360/ 6.0dBi 55% 30%

2 Sector 90/ 16.5dBi 60% 40%

3 Sector 65/ 18.5dBi 65% 40%

4, 5 Sector 65/ 18.5dBi 75% 40%

Macrocell

6 Sector 33/ 21.0dBi 85% 40%

UMTS Linkbudget and Capacity Analysis.pdf

Documents

Transcript of UMTS Linkbudget and Capacity Analysis.pdf