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Etisalat AcademyPage 1 of 31Anand Alexander

UMTS DOWNLINK BUDGET

"We see what we want to see unless we make a conscious effort to see

what is really there."

- Anon

Anand Alexander

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By the end of this session, the participants will be able to:

Differentiate between GSM and UMTS link budgets

Consider all the UMTS parameter network interactions in the UMTS uplink anddownlink budget

Estimate the log normal fade margin for a % age area coverage

Calculate the uplink load factor

Illustrate the concept of uplink intra-cell noise rise and its impact on range.

Illustrate how inter-cell interference limits the effective capacity of a cell.

Objectives

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The Downlink Link Budget Dilemma!

Downlink Range is highly dependent upon all the MobilesPositions and their individual Power Consumptions from theBase Station

UplinkRange

DownlinkRangeUplinkRange

DownlinkRange

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UMTS Downlink Link Budget

Uplink

Range

DownlinkRange Uplink

Range

DownlinkRange

UplinkRange

DownlinkRange

UplinkRange

DownlinkRange

1 2

3 4

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Max

PathLoss

Rx

Sensitivity

AntennaGain

BodyLosses

Penetr-

ationLosses

LogNormalFade

Margin

AntennaGain

DiversityGain

FeederLosses-+ + -+= Tx Power - - -

ProcessingGainInterCellInt. IntraCellInt. Eb/NoTarget

Thermal

NoisePower

NoiseFigure+ + + - +

Log

NormalFade

Margin

Soft

HandoverGain

-

Eb/NoTarget

FastFade

Margin-

BaseStation

Max.

Power

PowerConsumedIn Common

Channels

PowerConsumed

For

Handovers

PowerConsumedBy Other

Users

- - -

Other

UsersUplinks

Other

UsersLocations

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Downlink Range is dependent upon: Usual Link Parameters (Losses, Gains, etc.)

Intracell Interference (from other user channels on base site)

Intercell Interference (from other base sites)

Available Downlink Power, which depends upon

Current Power Consumption, which depends upon The number of mobiles

Their Eb/No Downlink Targets

Their Datarates

Their Activity Factors

Their locations (distances from Base Site)

etc, etc.


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Downlink Link Budget

Uplink

Range

Downlink

Range

Equal Distribution

Uplink

Range

DownlinkRange

Edge Distribution

We need to know all mobile

positions to be able to model the

downlink.

We can use some assumptions,

like assuming that all mobiles areat the cell edge, or are somehow

equally distributed.

Even with such assumptions the

Link Budget becomes a complex

task.

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Intra cell Interference (1/2)

In the Downlink the Intracell Interference is different.

The Uplink is Asynchronous

In the Uplink the Air Interface uses the OVSF Tree to allocate different

datarates for a particular user, and therefore datarate can change on a

frame by frame basis.

In the Uplink the Air Interface uses the Scrambling codes to separate

different uses in the same Cell.Scrambling codes are of equal length and have good cross-correlation

properties (time shifted versions have low cross-correlation values).

As Uplink is Asynchronous we will receive time shifted versions of the

Scrambling Codes due to unsynchronised access, and dispersion in the

radio channel.

In the Uplink we preserve Orthogonality between users due to the propertiesof the Scrambling code. We do not have to consider Interference due to

degraded Orthogonality.

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Intra Cell Interference (2/2)

In the Downlink the Intracell Interference is different.

The Downlink is Synchronous

In the Downlink there is only one OVSF Tree and the Air Interface uses the

OVSF Tree to separate different users in the same Cell.

In the Downlink the Air Interface uses rate adaptation and discontinuous

transmission to cater for different datarates for a particular user.In the Downlink the Air Interface uses the Scrambling Codes to separate

different Cells in the network.

OVSF codes have poor cross-correlation properties (time shifted versions

have high cross-correlation values). Orthogonality is only preserved

when not time shifted, and hence the need for the Downlink to be

Synchronised.Dispersion in the Radio Channel can cause Energy to be time shifted and

hence degrade Orthogonality between different users channels on the

Downlink.

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DOWNLINK LOAD FACTOR

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Load Factor

Receiver noise floor PN

K Boltzmann constant, = 1.38

T Kelvin temperature, normal temperature 290 K

W Signal bandwidth, WCDMA signal bandwidth 3.84MHz

NF: Receiver noise figure

10log(KTW) = -108dBm/3.84MHz

NF = 7dBUE typical value

NFWTKPN )**log(10

KJ/10 23

MHzdBmNFWTKPN

84.3/101)**log(10

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Interference from users of same cell

The downlink users are identified with the mutually orthogonal OVSF codes.

In the static propagation conditions without multi-path, no mutual

interference exists.

In case of multi-path propagation, certain energy will be detected by the

RAKE receiver, and become interference signals. Define the orthogonal factor to describe this phenomenon.

PT is a total transmitting power of NodeB, which includes the dedicated

channel transmitting power and the common channel transmitting power

1 Town jjj

PI

PL

N

jCCHTPPP

1

ownI

Load Factor

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Interference from users of adjacent cell

The transmitting signal of the adjacent cell BTS will cause interference to

the users in the current cell. Since the scrambles in use are different, such

interference is non orthogonal.

Assume the service is distributed evenly, transmitting power of all NodeBs

will be equal. In the system, there are K adjacent cell NodeBs, where path

loss from the number k NodeB to the user j is PLk,j. Hence we obtain:

K

jk

TjotherPL

PI1 ,

1

otherI

Load Factor

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N

K

jk

T

j

T

j

NotherownTOT

PPL

PPL

P

PIII

1 ,

11

Suppose the power control is desired, we obtainSuppose the power control is desired, we obtain

jjjTOT

j

j

jvR

W

I

PL

P

NoEb1

/

ThenThen

jjTOTj

j

jjPLIv

W

RNoEbP /

AnalysisDownlink Interference Composition

Load Factor

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jN

K

jk

j

TTj

N

j

j

jCCH

N

K

jk

T

j

T

j

N

jj

j

jCCH

N

jjTOTj

j

jCCHT

PLPPL

PLPPv

W

RNoEbP

PPL

PPL

PPLv

W

RNoEbP

PLIvW

RNoEbPP

1 ,1

1 ,1

1

1/

11/

/

N

jCCHTPPP

1

Because

Downlink Interference Analysis

Then

Load Factor

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N

j

j

jjj

N

jj

j

jNCCH

T

vW

R

NoEbi

PLvW

RNoEbPP

P

1

1

/11

/

K

jk

jj

PLPLi

1 ,

Resolve PT to obtain

where i j is the adjacent cell interference factor of the user, defined as:


Load Factor

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N

j

j

jjjDLv

W

RNoEbi

1

/1


According to the analysis, we can define the downlink load factor:

As different from the theoretic calculation of uplink capacity, and in the

downlink capacity formula are variable related to user position. Namely, the

downlink capacity is related to the spatial distribution of the users, and can

only be determined through system emulation.

Load Factor

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Load Factor

M

j

j

j

jo

b

DLW

R

N

Ei 1

Average Downlink Load Factor is presented, based upon usingaverage values for the Orthogonality factors, j, and Other Cell to

Own Cell Powers, ij. This results in a modified equation as:

If all Musers in the Cell were using the same type of service, then

Eb/No, Activity Rate, and Bit Rate would be the same.

In this case we can state that the Average Downlink Load Factor,

DL can be expressed as:

W

R

N

EMi

o

b

DL1

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Emulation Result

When Node B Tx is 43dBm(20W), the maximum numberof users is approx. 114

To ensure system stability, themean Tx power of Node B

should not be more than 80%of the maximum Tx power, 42dBm. This way, the supportednumber of users is 110

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Coverage/Capacity

Downlink Noise Rise as a Function of Downlink Data Throughput and

i for avg = 0.6 (ITU Vehicular A Channel)

0

2

4

6

8

10

12

14

16

18

20

0 1000 2000 3000 4000 5000 6000

Throughput (kbps)

NoiseRise(dB)

10%

25%

50%

75%

90%

Average i

Downlink Noise Rise as a Function of Downl ink Data Throughput and

i for avg = 0.9 (ITU Pedestrian A Channel)

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

0 1000 2000 3000 4000 5000 6000

Throughput (kbps)

No

iseRise(dB)

10%

25%

50%

75%

90%

Average i

Downlink Noise Rise as a function ofdata throughput.

Assumes:

Eb/No = 5.5dB

User Average i= 10% to 90%

LCD144 Users

User Average a = 0.6 and 0.9 50% Cell Load

Intercell Interference (from iavg) andIntracell Orthogonality (from aavg)limits Pole Capacity

Intracell Interference (additionalthroughput) limits range

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Coverage/Capacity

UMTS Dow nlink Range as a function of Capacity and Average User i

for avg = 0.6 (ITU Vehicular Channel A)

0

1

2

3

4

5

6

0 1000 2000 3000 4000 5000 6000

Throughput (kbps)

Range(km)

10%

25%

50%

75%

90%

UMTS Down link Range as a function of Capacity and Average User i

for avg = 0.9 (ITU Pedestrian Channel A)

0

1

2

3

4

5

6

0 1000 2000 3000 4000 5000 6000

Throughput (kbps)

R

ange(km)

10%

25%

50%

75%

90%

Average i

Average i

DownlinkRange as a function of datathroughput.

Assumes:

BS Power = 20W

Eb/No = 5.5dB

User Average i = 10% to 90%

LCD144 Users User Average = 0.6 and 0.9

50% Cell Load

Intercell Interference (from iavg) andIntracell Orthogonality (from aavg)limits Pole Capacity

Intracell Interference (additional

throughput) limits range

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Coverage/Capacity

Uplink and Downlink range as a function of

capacity, or throughput, are shown together.

LCD144 Services

Uplink:

Eb/No = 1.5dB

i = 0.65

Downlink:

Eb/No = 5.5dB

iavg = 0.8

aavg = 0.6

UMTS Uplink and Downlink Range as a function of Uplink and Downlink

Capacity

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 500 1000 1500

Load (kbps)

CellRadius(km)


Capacity

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 500 1000 1500

Load (kbps)

CellRadius(km)


Capacity

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 500 1000 1500

Load (kbps)

CellRadius(km)


Capacity

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 500 1000 1500

Load (kbps)

CellRadius(km)

Downlink Coverage/Capacity values forcombinations of User Positions, and Cell Loading

I.e. due to User Movement and Loading

Uplink Coverage/Capacity values forcombinations of Cell Loading.

Downlink

Uplink

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Coverage/Capacity

In WCDMA/UMTS there exists awhole range of possible Capacity

and Coverage combinations, based

upon Service Mixes, user speeds,

Interference Geometry, User

Positions, Channel Multipath, etc,

etc.

In contrast with GSM there existsessentially one Capacity/Coverage

point, and is not dependent upon

user locations, Service mix, user

speeds, etc.

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Impact of Soft(er) Handover

Handover Area where DownlinkPilot Power is within xdB of

each other and within Range

Large Handover Area = GoodResilience for MS at cell edge, given

that Cell can breathe, but lowercapacity

Small Handover Area = PoorResilience for MS at cell edge, giventhat Cell can breathe, but higher

capacity

75%Load Range

75%Load Range

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Impact of Soft(er) Handover

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LINK BUDGET ANALYSIS

We shall look at the impact on the Network Design of:

Antenna Downtilt

Antenna Sectorisation

Mast Head Amplifiers

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Network Simulation

Parameters used in simulation.

13.5km2 of Tokyo

10 Sites, 50m Height

20W Base Station Power

15dB Penetration Losses = 12dB

Channel Profile = ITUVehicular 3km/h

Average UserOrthogonality,

avg

= 0.5

Soft Handover AdditionWindow = 4dB

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Analysis

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Antenna Tilts

With Antenna Downtilt, one would expectthe Intercell Interference to be better

contained, at the expense of reducing

Coverage Quality.

The Table shows the results obtained four

types of Antenna.

The graph homes in on the tri-sectoredantenna.

i decreases with Tilt Angle

No. of Users increase with Tilt

Angle

Coverage increases then decreases

with Antenna Tilt

Antenna Tilt

Other/Own Cell

Interference

Ratio, i

Served

Users

Soft

Handover

Overhead8kbps 64kbps 144kbps

0o

0.79 239 28% 70% 32% 40%

0o 0.88 575 40% 86% 59% 62%

4o

0.75 624 39% 91% 71% 72%

7o

0.59 697 36% 92% 76% 76%

10o 0.37 856 30% 90% 75% 74%

14o

0.38 787 32% 81% 62% 61%

0o 1.09 604 41% 92% 70% 71%

4o

0.94 707 30% 95% 81% 81%

7o

0.72 833 26% 96% 84% 83%

10o 0.47 959 21% 94% 82% 81%

14o

0.50 886 26% 86% 69% 68%

0o 1.15 880 48% 93% 76% 76%

4o 1.03 946 49% 96% 83% 83%

7o

0.88 1037 45% 96% 85% 84%

10o 0.73 1054 41% 95% 83% 82%

14o

0.58 930 33% 86% 70% 69%

UL Coverage Probability

3-Sectored, 65o

4-Sectored, 65o

6-Sectored, 65o

Omni

Uplink i and Cell capacity as a Function of Antenna Tilt

for 3-Sectored 65o

antennas

0

100

200

300400

500

600

700

800

900

0 2 4 6 8 10 12 14

Antenna Tilt

Numbe

rofUsers

(Capacity)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

OtherCe

ll/OwnCell

Interfe

rence,i

Served Users

Other/Own Cell Interference Ratio, i

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Antenna Beamwidth

MHA in use, No Downtilt, MS Tx

Power = 24dBm Max.

Higher Sectorisation, More Capacity

per site achieved.

Narrower Beamwidth results in lower

Other Cell to Own Cell Interference.

Narrow Beamwidth results in moreCapacity and Reduction in SoftHandover Overhead

Coverage Probability has an Optimum

value.

Antenna

Beamwidth

Other/Own Cell

Interference

Ratio, i

Served

Users

Soft

Handover

Overhead

8kbps 64kbps 144kbps

360o

0.79 240 28% 70% 32% 40%

120o

1.33 441 39% 85% 50% 59%

90o

1.19 461 35% 87% 55% 62%

65o 0.88 575 34% 86% 59% 62%

120o 1.72 489 54% 90% 62% 68%

90o 1.49 510 51% 92% 67% 72%

65o

1.09 604 41% 92% 70% 71%

33o

0.92 691 40% 88% 65% 64%

120o

2.18 593 64% 95% 75% 79%90

o1.97 627 59% 96% 80% 82%

65o 1.43 758 55% 96% 80% 81%

33o 1.15 880 48% 93% 76% 76%

6-Sectored


Omni

3-Sectored

4-Sectored

Uplink Coverage probability and Users Served as a Function

of Antenna Sectorisation and Beamwidth

84%

86%

88%

90%

92%

94%

96%

98%

0 100 200 300 400 500 600 700 800 900 1 000

No. of Users

Coverage

Probability(8Kbps 3-Sectored 120deg

3-Sectored 90deg3-Sectored 65deg4-Sectored 120deg4-Sectored 90deg4-Sectored 65deg6-Sectored 120deg6-Sectored 90deg6-Sectored 65deg

6-Sectored 33deg4-Sectored 33deg

3-sectors

4-sectors

6-sectors

Uplink Coverage probability and Users Served as a Function

of Antenna Sectorisation and Beamwidth

84%

86%

88%

90%

92%

94%

96%

98%

0 100 200 300 400 500 600 700 800 900 1 000

No. of Users

Coverage

Probability(8Kbps 3-Sectored 120deg

3-Sectored 90deg3-Sectored 65deg4-Sectored 120deg4-Sectored 90deg4-Sectored 65deg6-Sectored 120deg6-Sectored 90deg6-Sectored 65deg

6-Sectored 33deg4-Sectored 33deg

3-sectors

4-sectors

6-sectors

90o

120o65o

120o

120o

90o

65o

65o90o

33o

33o

L N i M H d A lifi (MHA) U li k

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Low Noise Mast Head Amplifier (MHA) on Uplink

MHA

Other/Own CellInterference

Ratio, i

ServedUsers in

UL

Servedusers in

DL

8kbps 64kbps 144kbps

no MHA 0.60 1038 807 93% 78% 78%

with MHA 0.61 1064 746 95% 82% 82%

no MHA 0.73 1089 884 96% 86% 85%

with MHA 0.73 1107 846 98% 89% 89%

no MHA 0.88 1124 1052 97% 87% 86%

with MHA 0.90 1132 1021 98% 90% 90%


3-Sectored, 65o

4-Sectored, 65

o

6-Sectored, 65o

Antenna Tilt = 7o

; MS Power = 27dBm Increase in Number of UL users with MHA

Decrease in Number of DL users with MHA

Increase in UL Coverage Probability with MHA

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Question and Answers

Discussion

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