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  1. HEW SG PHY Considerations For Outdoor Environment • Date:2013-05-12 Authors: Wookbong Lee, LG Electronics

  2. Abstract • This document includes PHY considerations for HEW development especially for Outdoor Environment. Wookbong Lee, LG Electronics

  3. Introduction • IEEE 802.11a/b/g/n/ac have been developed focusing on indoor usage cases. • Even though the indoor usage case will be one of the major environment for HEW project, we also need to consider outdoor environment as well. [1] • Outdoor channel environment is quite different from indoor channel model as measured and modelled in [2][3]. • In this contribution, we analyze major characteristics of outdoor channel model (urban macro cell (UMa)). Wookbong Lee, LG Electronics

  4. Delay Spread • Following figures shows CDF of the maximum excess delay for UMa channel model at 2.4GHz Wookbong Lee, LG Electronics

  5. Delay Spread • Following figures shows CDF of the maximum excess delay for UMa channel model at 5GHz Wookbong Lee, LG Electronics

  6. Impact of Larger Delay Spread • Performance loss due to larger inter-symbol-interference. • There is no other solution than increasing CP length in this case. • Just increasing CP length brings throughput loss due to larger PHY overhead. (See Appendix for more details) • During the development of IEEE 802.11afor .11ah, members come up with increasing CP length by increasing FFT size for a given bandwidth to maintain physical layer overhead. • For example, the subcarrier spacing of .11af is 41.7kHz (in case of U.S. channel) and that of .11ah is 31.25kHz while the subcarrier spacing of .11a/n/ac is 312.5kHz. • With same logic, we can increase CP length by increasing FFT size for a given bandwidth (20MHz, 40MHz, 80MHz or 160MHz). Wookbong Lee, LG Electronics

  7. Impact of Larger Delay Spread Wookbong Lee, LG Electronics

  8. Impact of Larger Delay Spread Wookbong Lee, LG Electronics

  9. Channel Variation • In outdoor channel, per tone channel is varying faster than that in indoor channel due to faster environmental change as well as more channel tap (more multi-path) Wookbong Lee, LG Electronics

  10. Impact of Larger Channel Variation • Channel variation of one tone per one OFDM symbol • Observation during the PPDU max Time • In 802.11 ac, aPPDUMaxTime is 5.484 ms Wookbong Lee, LG Electronics

  11. Impact of Larger Channel Variation • Channel variation of one tone per 1ms • It is possible to check that channel is very fast change in outdoor Wookbong Lee, LG Electronics

  12. Design Consideration Points for HEW Wookbong Lee, LG Electronics

  13. Wookbong Lee, LG Electronics Appendix

  14. Performance result for just increasing CP Wookbong Lee, LG Electronics

  15. Channel Model * (μ,σ) For SNR evaluation, we assume noise figure 5dB, cable loss 2dB, signal power 1W for 20MHz. See page 30-41 of reference [2] Wookbong Lee, LG Electronics

  16. Channel Model hBS = 25 m, hUT = 1.5 m, d′BP= 4 h′BSh′UTfc/c, h′BS = hBS – 1.0 m, h′UT = hUT – 1.0 m Wookbong Lee, LG Electronics

  17. Delay profile vs. CP length • And we need to have proper modeling on how channel and CP impact performance. • One of possible modeling is as follows [4]: TFFT is FFT period CP is CP period |αm|2 is power of m-th tap τm is delay of m-th tap including OFDM symbol timing Wookbong Lee, LG Electronics

  18. Delay profile vs. CP length • Modified SINR by equations in previous slide matches performance of without ISI Wookbong Lee, LG Electronics

  19. Simulation Assumption for Slide 7 and 8 Wookbong Lee, LG Electronics

  20. HTTP traffic [4] • Main Object Size (Truncated Lognormal: μ=8.37, σ=1.37, Min=100byte, Max=2Mbyte) • Embedded Object Size (Truncated Lognormal: μ=6.17, σ=2.36, Min=50byte, Max=2Mbyte) • Number of Embedded Objects per page (Truncated Pareto: α = 1.1, k=2, Max = 53) Mean: 8,728byte Wookbong Lee, LG Electronics

  21. References • [1] IEEE 802.11-13/0331r5- Laurent Carious et al., “High- efficiency WLAN,” March 2013 • [2] Report M.2135, “Guidelines for evaluation of radio interface technologies for IMT-Advanced, ” available at http://www.itu.int/pub/R-REP-M.2135 • [2] IST-4-027756 WINNER II D1.1.2 V1.2, “WINNER II channel models,” available at http://www.ist-winner.org/deliverables.html • [3] MickaelBatariere, Kevin Baum, and Thomas P. Krauss, “Cyclic Prefix Length Analysis for 4G OFDM Systems,” VTC 2004 Fall • [4] IEEE 802.16m-08/004r5, “IEEE 802.16m Evaluation Methodology Document (EMD),” Jan. 2012 Wookbong Lee, LG Electronics