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Modelling of physical layer behaviour in a HS-DSCH network simulator

Modelling of physical layer behaviour in a HS-DSCH network simulator. Frank Brouwer Twente Institute for Wireless and Mobile Communications. Overview. Network simulator Link adaptation Physical layer model requirements Hybrid ARQ Modeling for network simulator Narrow band modeling

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Modelling of physical layer behaviour in a HS-DSCH network simulator

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  1. Modelling of physical layer behaviour in a HS-DSCH network simulator Frank Brouwer Twente Institute for Wireless and Mobile Communications

  2. 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

  3. 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

  4. 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 loss • Shadowing (correlation distance) • Channel model (Vehicular A, Pedestrian A, Indoor A, …) • Physical layer characteristics • BLER per TTI • Link adaptation, Hybrid ARQ

  5. Link adaptation • Keep BLER constant by changing Transport Block Size • More data under good channel conditions • UE transmits CQI:max TBS with BLER = 0.1 • Node-B decides TBS:CQI + own algorithm

  6. 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

  7. 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 Node B UE PDU NACK PDU PDU PDU Erroneous PDU + = Success ACK

  8. 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

  9. 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 10 10 Narrow band modeling

  10. Channel RAKE fingers 10 Signal Interference 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 Received signal

  11. Wide band modeling (2) • Symbol time options: • Raw symbols (240 ksymbols/s for all CQI) • Bitrate including overhead • Bitrate excluding overhead • Corrections needed for ISI performance of receiver • Example: • Vehicular A •  is 0.3 times bitrate excluding overhead

  12. 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

  13. Physical layer behaviour • SNR generated from channel model • BLER generated from PHY model • Observations: • CQI lags to SNR (delay in reporting • Actual BLER strongly varying • Rounding of CQI • Lagging of CQI (“wrong” selection of TBS)

  14. 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

  15. 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

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