11Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Modelling of physical layer behaviour in a HS-DSCH

network simulator

Frank BrouwerTwente Institute for Wireless and Mobile

Communications

22Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Overview

Network simulator• Link adaptation• Physical layer model requirements• Hybrid ARQ

Modeling for network simulator• Narrow band modeling• Wide band modeling

Physical layer behaviour Conclusions

33Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Overview

Network simulator• Link adaptation• Physical layer model requirements• Hybrid ARQ

Modeling for network simulator• Narrow band modeling• Wide band modeling

Physical layer behaviour Conclusions

44Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Network simulator

End-to-end performance analysis HSDPA Streaming video, web browsing, file transfer Mutual influence PHY, MAC, RLC <> IP, TCP/UDP

• Detailed implementation of MAC, RLC, IP, TCP/UDP• Abstract and realistic model PHY

Abstract PHY model• Channel conditions

Distance lossShadowing (correlation distance)Channel model (Vehicular A, Pedestrian A, Indoor A, …)

• Physical layer characteristicsBLER per TTILink adaptation, Hybrid ARQ

55Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Link adaptation

Keep BLER constant by changing Transport Block Size

More data under good channel conditions

0

5000

10000

15000

20000

25000

30000

TBS

12345678910111213

CQI generation

-16

-14

-12

-10

-8

-6

-4

-2

0 20 40 60 80 100 120 140 160 180 200

TTI

SN

R (d

B)

0

2

4

6

8

10

12

14

CQ

I

SNR

CQI

UE transmits CQI:max TBS with BLER = 0.1

Node-B decides TBS:CQI + own algorithm

66Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Physical layer model requirements

Condition in network simulator includes:• 30 Transport Block Sizes• Any SNR value (-20 to 15 dB continuous)

Required output• Monotonous relation SNR – BLER for given TBS• More focus on relative than on absolute accuracy• One BLER value per TTI

Calculation should not require more that some (tens of) floating point operations

77Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

PDUPDUPDU

Hybrid ARQ Reception in error => combine received signal with a

second reception Possible H-ARQ schemes

• Incremental redundancy (Send additional information)• Chase combining (Repeat the same information)

Chase combining assumed

Maximum Ratio Combining (= add powers)• Power of first reception aids second reception• Higher probability of successful reception

PDU+ = PDU

ErroneousSuccess

Node B UE

NACKACK

88Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Overview

Network simulator• Link adaptation• Physical layer model requirements• Hybrid ARQ

Modeling for network simulator• Narrow band modeling• Wide band modeling

Physical layer behaviour Conclusions

99Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Narrow band modeling

Generate a varying SNR in network simulator• All received power of wanted signal is captured• PHY layer behavior equal to AWGN

WP2 PHY AWGN simulations as input Modeled through analytical approximation

• Shape of curve equal for all CQI• Steepness function of CQI• Offset function of CQI

• Can generate for each CQI,SNR and BLER

CQI = Channel Quality Indicator

BLER vs SNR simulation and model

0.01

0.1

1

-20 -15 -10 -5 0 5 10 15

SNR (dB)

BLE

RCQI1 sim CQI22 sim CQI1 anal CQI22 anal

CQI8 sim CQI30 sim CQI8 anal CQI30 anal

CQI15 sim CQI15 anal

3.1703.1

)...1(log2

)(log3 7.01010

CQI

BLERCQISNR 1010

1010Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Wide band modeling (1)

Channel produces delayed copies

RAKE receiver:• Estimate tap delay line• One finger per tap• Maximum Ratio Combine

ISI model: All power over symbol border turns into noise

Transmitted signal

Channel

Received signal

RAKE fingers

Signal Interference

N

iit

N

i

niit

nt

p

pisi

1,

1,

,

))1(

(log10

1,,

1,,10

nisip

isipSNR N

iitit

N

iitit

t

10

1111Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Wide band modeling (2)

Symbol time options:Raw symbols (240

ksymbols/s for all CQI)Bitrate including overheadBitrate excluding overhead

Corrections needed for ISI performance of receiver

Example:• Vehicular A is 0.3 times bitrate

excluding overhead

0.01

0.1

1

-20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0 15.0

SNR (dB)

BLER

CQI1 sim CQI15 sim CQI1 anal CQI15 anal

CQI8 sim CQI8 anal CQI22 anal

1212Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Overview

Network simulator• Link adaptation• Physical layer model requirements• Hybrid ARQ

Modeling for network simulator• Narrow band modeling• Wide band modeling

Physical layer behaviour Conclusions

1313Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Physical layer behaviour

SNR generated from channel model

BLER generated from PHY model

Observations:• CQI lags to SNR (delay in

reporting• Actual BLER strongly

varyingRounding of CQILagging of CQI (“wrong”

selection of TBS)

CQI generation

-16

-14

-12

-10

-8

-6

-4

-2

0

0 50 100 150 200TTI

SNR

(dB

)

0

2

4

6

8

10

12

14

16

CQ

I

SNRCQI

Resulting BLER

1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

0 50 100 150 200TTI

BLER

1414Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Overview

Network simulator• Link adaptation• Physical layer model requirements• Hybrid ARQ

Modeling for network simulator• Narrow band modeling• Wide band modeling

Physical layer behaviour Conclusions

1515Session 2, Presentation: Modelling of physical layer behaviour in a HS-DSCH network simulator

Conclusions

Network level simulations need “simple” model covering all CQIs and all SNRs• No physical layer simulations• No difficult look-up structures

Physical layer model provides subset Analytical model matches perfectly in narrow

band channel conditions Model adaptation for wide band channel

conditions has sufficient match