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Spatial Reuse and Coexistence with Legacy Devices

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  1. Spatial Reuse and Coexistence with Legacy Devices Date:2014-05-13 Authors: James Wang et. al., MediaTek

  2. Background • Several contributions [references 1-10] show that significant network throughput improvements can be achieved via spatial re-use using higher CCA, TPC, DSC, or combination of these. • However, some co-existence issues are observed from the simulation results • Starvation of legacy devices, when legacy devices co-exist with the spatial reuse devices • Higher collision • This contribution analyze these issues and explore the fairness basis for co-existence with legacy devices James Wang et al, MediaTek

  3. Channel Access Issues in Dense Environment Ref 11 provides a real life scenario of a dense deployment campus network which shows high channel busy condition (low likelihood of channel access) despite high percentage (>50%) of STAs transmit with highest MCS James Wang(MediaTek)

  4. Starvation of Legacy Devices • STA3 and STA4 use spatial re-use during TXOP 1 to access the channel, it delays the legacy STAs channel access window from the end of TXOP1 to the end of TXOP 2. • STA3 and STA4 have unfair advantage (over legacy devices) for channel access  the starvation of legacy devices during co-existence. James Wang et al, MediaTek

  5. Fairness to Legacy Devices The fairness issue during spatial re-use can be addressed with the medium sharing rules (from 11ah Clause 9.48.4) which mandates spatial-reuse TXOP (TXOP2) to end at or before the expiration of TXOP 1. James Wang et al, Mediatek

  6. Higher Collision Issue • The spatial re-use STAs should reduce its transmit power level during spatial reuse to prevent causing collisions to legacy STAs. Spatial Reuse STA 3 Legacy STA1 Legacy STA2 • Spatial reuse STA using higher CCA levels can transmit in the middle of a TXOP owned by a legacy STA, which operates at lower CCA levels, potentially causing collision to legacy STA, resulting in • higher power consumption due to re-transmission • reduced throughput James Wang et al, Mediatek

  7. TPC during Spatial Re-use STA AP TX Pwr TX PWR Reduction = CCI AP TPC SpaceLoss CCI SpaceLoss CCI CCI Spatial re-use STA CCA CCA Noise floor Noise floor • A reasonable transmit power level for the spatial reuse device is to reduce TX PWR by CCI (co-channel interference) • This transmit control is only used during spatial re-use and is based on the received CCI. (Note that spatial reuse STA needs to operate at high noise level (CCA+CCI)) James Wang et al, MediaTek

  8. Spatial Detection Window Spatial Reuse CCI 1 Legacy STA1 CCI 1 STA 3 CCI 2 CCI2 Legacy STA2 • Since there are two STAs involved in a frame exchange, the spatial re-use STA should consider CCIs from both STAs involved in the frame exchange. • TPC power level for spatial re-use STAs should be TX PWR reduction = max(CCI1, CCI2) • Spatial reuse STA uses a spatial detection window to measure CCI 1 and CCI 2 before transmission James Wang et al, Mediatek

  9. Conclusions and Future Works • This contribution discusses the legacy device starvation issues due to spatial re-use as observed from previous contributions • This contribution proposes mechanisms to achieve fairness for co-existence with legacy STAs when spatial re-use is used. • Spatial re-use should have independent channel contention and its TXOP should be confined within the duration original TXOP • Transmit power of the spatial reuse STAs should be constrained as described in Slide 7 (or 6) • Future work • Simulation results for the use case scenarios will be presented • Further investigation of transmit power control mechanism for spatial re-use James Wang et al, Mediatek

  10. References Ron Porat, Broadcom, 11-14-0082-00 Improved Spatial Reuse Feasibility - Part I Jinjing Jiang, Marvell, 11-14-0372-00 System level simulations on increased spatial reuse Graham Smith, DSP Group, 11-14-1290-01 Dynamic Sensitivity Control for HEW Graham Smith, DSP Group, 11-14,0294-02 Dynamic Sensitivity Control Channel Selection and Legacy Sharing Imad Jamil, Orange, 11-14-0523-00-00ax Mac Simulation Results for DSC and TPC Graham Smith, DSP Group, 11-14-0328-02 Dense Apartment Complex Throughput Calculations Graham Smith, DSP Group, 11-14-0045-02 E-Education Analysis Graham Smith, DSP Group, 11-14-0058-01 Pico Cell Use Case Analysis Graham Smith, DSP Group, 11-13-1489-05 Airport Capacity Analysis Graham Smith, DSP Group, 11-13-1487-02 Apartment Capacity - DSC and Channel Selection Chingwa Yeh, MediaTek, 11-14-0648-00 Performance Observation of a Dense Campus Network r0 James Wang et al, Mediatek