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OBSS Issue and Simulation Scenarios in TGac

This paper discusses the OBSS (Overlapping Basic Service Set) issue in TGac and compares it with TGaa, focusing on video streaming. It examines measured propagation loss in a typical Japanese apartment and presents OBSS simulation scenarios in TGac.

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OBSS Issue and Simulation Scenarios in TGac

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  1. OBSS issue and simulation scenarios in TGac Authors: Yasushi Takatori (NTT)

  2. Outline • Background • Measured propagation loss in a typical Japanese apartment • Difference between OBSS issue in TGac and that in TGaa • OBSS simulation scenarios in TGac • Video Streaming with 11ac devices Yasushi Takatori (NTT)

  3. Background • TGac agrees that it is important to see how 11ac devices behave in OBSS [1]. • TGaa has addressed OBSS issue for video streaming. Frequency channel assignment and time sharing mechanism have been developed to support video streaming[2]. • OBSS in TGac is caused by both possible frequency band enlargement and increase in the number of WLAN devices. • The behavior of 11ac devices in OBSS should be examined not only for video streaming but also for othertraffic. Yasushi Takatori (NTT)

  4. TG ac Ad Hoc groups discussion topics doc.:IEEE 802.11-09/1175r1 TG ac Coex PHY MAC MU- MIMO • OBSS Management • Multi-Channel • Non-contiguous channelization • MC MAC protocol • > 80MHz channel • Backwards compatibility • CCA • Channel access Fairness • Scanning and channel selection Pilots Data tones Preamble Enhanced MCS Sounding Higher Bandwidth modulation Parsing and Interleaving Coding, STBC Spatial Mapping & Cyclic Delays • Power saving • Capability negotiations • Frame formats Downlink MU-MIMO Uplink MU-MIMO MU-MIMO parameters (e.g. # of streams, # of clients) Training protocols ACK protocols Reservation/polling protocols Yasushi Takatori (NTT)

  5. Measured propagation loss in a typical Japanese apartment Yasushi Takatori (NTT)

  6. Measurement place 3.0 m 6 7.3 m 1 2 3 4 5 7 Yasushi Takatori (NTT)

  7. Layout of each room in the measurement place 7.3 m 1 S2 S1 S5 3.0 m S3 S4 2 S * APNumber of antennas = 8, Linear array (Spacing 0.5λ) STANumber of antennas = 4, Linear array (Spacing 0.5λ) Yasushi Takatori (NTT)

  8. D/A D/A D/A D/A Measurement equipment 4x8 MIMO channel measurement was carried out for SDMA evaluation. Long preamble signal is continuously transmitted. Interference between two APs or AP/STA is assumed in this measurement. Tx (STA) : 4 element h = 2.12/0.9, 0.75 m Rx (AP) : 8 element h = 2.12 m AGC LNA Up-conv. Down-conv. HPA A/D AGC LNA Up-conv. Down-conv. HPA A/D AGC Up-conv. LNA Down-conv. HPA A/D Up-conv. HPA AGC LNA Down-conv. A/D Channel estimator TCP-IP Yasushi Takatori (NTT)

  9. AP AP STA Image of interference from OBSS (other person’s room) (my room) (desired) (OBSS) Measured path STA (OBSS) (desired) Yasushi Takatori (NTT)

  10. Measurement parameters • Frequency 4.85 GHz • Bandwidth 40 MHz (20MHz x 2) • Signal OFDM signal • Number of FFT 128 • Number of subcarrier 96 (Legacy .11a mode) • Antenna height 2.12 m (Rx side) 0.75m (Tx side) Yasushi Takatori (NTT)

  11. AP AP Results on Interference power ~ Horizontal neighborhood rooms~ (Case 1) (Case 1) [dBm] 3m -74.46 -76.54 -68.28 -69.18 -64.63 -63.52 -56.89 -56.23 -50.18 -45.79 Averaged. height = 2.12 m (Case 2) (Case 2) [dBm] -78.61 -69.98 -65.73 -55.57 -41.39 3m height = 0.9 m Yasushi Takatori (NTT)

  12. -22 -32 -42 -52 -62 -72 -82 -92 TGn Model [3] Measurement Result Measurement result agrees with the path-loss model in TGn [2]. Relative Received Power [dB] Indoor propagation loss formula (11n) *, F in MHz, d in feet For d<16.5ft Lp = – 38 + 20 log F + 20 log d + Wall/Floor loss (Free Space formula) For d>16.5ft Lp = – 38 + 20 log F + 20 log 16.5 + 35 log (d/16.5) + Wall/Floor Loss Yasushi Takatori (NTT)

  13. Summary for measured propagation loss • When considering the interference betweens rooms on horizontal direction, interference seems to be almost the same with the TGn model.[2] Hence, the model in TGn seems to be reasonable in the evaluation of OBSS in the apartment. • As well as described in [2], this result shows the influence on the interference by OBSSs is serious problem in Japanese apartment. • OBSS in TGac would be a serious problem because 80MHz bandwidth is likely to be used. Yasushi Takatori (NTT) Slide 13 K.Nishimori, T. Murakami, R.Kudo, Y.Takatori, Y.Asai (NTT)

  14. Difference between OBSS issue in TGac and that in TGaa Yasushi Takatori (NTT)

  15. OBSS issue in TGaa [2][3] OBSS issue in TGaa is focusing on video streaming. Frequency channel assignment and time sharing mechanism have been developed to support video streaming in OBSS. Simple competitionamong general traffic is considered to be sufficient. July xx, 2009 Information of QoS traffic load is advertised among multiple BSSs. QAP-1 QAP-2 Qload EDCA or HCCA EDCA or HCCA Frequency Channel K1 Frequency Channel K2 STA-11 STA-21 Slide 15 Yasushi Takatori (NTT) Names

  16. OBSS Issue in TGac • OBSS issue is important in TGac because frequency channel shortage is expected. • OBSS issue in TGac is not only for video streaming but also for other traffic. • Frequency channel assignment algorithm using TGaa approach may mitigate OBSS effect. • However, TGaa approach seems not to be directly applicable to 11ac because TGac should take into account other traffic also. Frequency band allocation in Japan 20MHz mode 5150 5250 5350[MHz] 40MHz mode 5190 5230 5270 5310 (80MHz mode) 5470 5725[MHz] 5510 5550 5590 5630 5670 5710 Yasushi Takatori (NTT)

  17. Direction • Time resource is fairly shared by CSMA/CA with RTS/CTS mechanism [2]. SDMA scheme in 11ac should not degrade this level of fairness. Sharing scheduling information among multiple BSSs may improve the throughput [5]. • Interference management has a potential to achieve further throughput improvement in OBSS. It has been also addressed in TGaa [2][3][4]. Yasushi Takatori (NTT)

  18. Possible Interference Management • Frequency domain: • Access mechanism that enables frequency channel assignment would be devised to use 80MHz bandwidth for all traffic.(For 11aa case, see [2]) • Falling back to narrowband mode,e.g. 20/40MHz mode, can be one of the practical solutions. (For 11aa case, see [3]) • Spatial domain.: • Transmission power control (TPC) might be effective to decrease the number of OBSSs. (TGh addressed TPC to avoid interference to other systems. Although it is effective in an apartment scenario, TPC might cause range limitation in other scenarios [4].) • Beamforming might be also useful because 11ac devices already have beamforming capability to enable MU-MIMO. Yasushi Takatori (NTT)

  19. Basic flow to mitigate influence of OBSS (1) OBSS detection • Carrier Sensing • Others (2) Exchanging control messages • RTS/CTS mechanism • TRM/Sounding signals • (Advertisement of Qload) • Others (3) Resource allocation • NAV setting • (Frequency channel selection) • (TPC/Beamforming ) (4) Data transmission (5) ACK (1) (3) (1) (3) (2) AP-1 AP-2 (2) (2) (2) (2) (4) (4) (5) (5) (2) STA-11 STA-21 Yasushi Takatori (NTT)

  20. Summary of possible approaches • OBSS issue is important in TGac because frequency channel shortage is expected. It is not only for video streaming but also for other traffic. • TGaa has addressed OBSS issue to support video streaming in OBSS. Other general traffic is not taken into account. • Frequency channel assignment and time sharing mechanism have been developed in TGaa to support video streaming in OBSS. • The following interference management approaches are suggested. • Frequency domain approach: • Modification of TGaa mechanism is one of the possible approaches. • Frequency channel assignment / Falling back to narrow band modes • Spatial domain approach: • Interference management with TPC / Beamforming Yasushi Takatori (NTT)

  21. OBSS Simulation Scenario in TGac There two scenarios, enterprise scenario [6] and home network scenario [7]. The following slides explain home network scenario with OBSS. Yasushi Takatori (NTT)

  22. Home Network Evaluation Scenario • To simplify OBSS scenario, the following effects are focused on. • Overlapping with 11ac • Overlapping with 11n • Effect of hidden terminals in OBSS • Throughput degradation from isolated Home Entertainment scenario • Evaluation model • BSS A: In-Home entertainment application • BSS B: 11ac with 3 STAs • BSS C: 11n with 3 STAs • Room walls are inserted to evaluate effect of hidden terminals Yasushi Takatori (NTT)

  23. AP and STA locations Attenuation factors of room wall and outside wall are TBD. In-home entertainment application 11n 11ac Yasushi Takatori (NTT)

  24. Channel Assignment • BSS A is identical to the BSS in TGac scenario #3 • BSS B is an 11ac BSS • BSS C is a upper 40MHz 802.11n BSS • Both 11ac have the same bandwidth (40MHz or 80MHz) Case 1 Case 2 Yasushi Takatori (NTT)

  25. Traffic flow at overlapping BSS B Flow number 1 and 12 in simulation scenario #3 are considered. Yasushi Takatori (NTT)

  26. Traffic flow at overlapping BSS C Flow No.1 in BSS B is changed to Flow No.1 of 802.11n scenario #1. Yasushi Takatori (NTT)

  27. References [1] Yasushi Takatori, “Importance of Overlapped BSS issue in 802.11ac,” Doc. IEEE802.11-09/0630r1. [2] Graham Smith, “TGaa OBSS Background,” Doc. IEEE802.11-09/0762/r0. [3] Graham Smith, “20/40MHz Channel Selection,” Doc. IEEE802.11-09/0740/r0. [4] Graham Smith, et al., “Overlapping BSS Proposed Solution,” Doc. IEEE802.11-08/0457/r3. [5] Yuichi Morioka, “Two Levels of OBSS Control in 11ac ,” Doc.IEEE802.11-09/0833/r0. [6] Brian Hart, Enterprise Simulation Scenario, IEEE 802.11-09/816r5, Sept. 22, 2009. [7] Yasushi Takatori, et al., Home Network Simulation Scenario with OBSS, Doc. IEEE802.11-09/1076r0. Yasushi Takatori (NTT)

  28. Video Streaming in 11ac • There seems to be three possibilities to support video streaming services with 11ac devices. (A) 11aa + 11ac: Simple combination (B) 11aa+ + 11ac: Creation of new standard, 11aa+ (C) 11ac only: Basic functions of 11aa are supported by 11ac • Question: Which one is suitable for video streaming services with 11ac devices? (A) 11aa + 11ac: (B) 11aa+ + 11ac: (C) 11ac only: Yasushi Takatori (NTT)

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