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MU-MIMO support for BSS load balancing

MU-MIMO support for BSS load balancing. Authors:. Date: 2010-07-13. Abstract.

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MU-MIMO support for BSS load balancing

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  1. MU-MIMO support for BSS load balancing Authors: Date: 2010-07-13 Daewon Lee, LG Electronics

  2. Abstract We discuss BSS load balancing in OBSS scenarios with MU-MIMO supporting APs and STAs. We analyze BSS load element in 11n and give general observations. Further discussions on how to support load balancing taking into account MU-MIMO operations seems needed. Daewon Lee, LG Electronics

  3. BSS load balancing without MU-MIMO • Example scenario with two AP with only legacy STAs • If BSS load of AP1 is lower than AP2 than association with AP1 will give better throughput for the STA Daewon Lee, LG Electronics

  4. BSS load balancing with MU-MIMO case 1 • Example scenario with two AP with legacy STAs and MU-MIMO supported STAs • In case BSS load of AP1 similar to AP2 and MU-MIMO supported STAs associated with each AP is different, association with which AP will give more benefits to the STA? Daewon Lee, LG Electronics

  5. Example of BSS load status (1/3) • Example timeline for an AP with only legacy STAs • BSS load is calculated by ratio of idle and busy time in a given measurement window • BSS load status definition will still work for SU-MIMO Daewon Lee, LG Electronics

  6. Example of BSS load status (2/3) • Example timeline for an AP with only MU-MIMO capable STAs • BSS load status definition does not take into account under utilized spatial streams which is available by MU-MIMO STA pairing Daewon Lee, LG Electronics

  7. Example of BSS load status (3/3) • Example timeline for an AP with legacy STAs and MU-MIMO capable STAs • BSS load status definition only give partial information of actual load and does not take into account spatial stream utilization Daewon Lee, LG Electronics

  8. BSS load balancing with MU-MIMO case 2 • Example scenario with two AP with MU-MIMO supported STAs • In case BSS load of AP1 similar to AP2, target STA associating with BSS with less spatial interfering STAs will be beneficial Daewon Lee, LG Electronics

  9. Examples of STA spatial interference footprint • Assuming STAs only utilize RSSI and BSS load • STAs which may have strong spatial interference between each other may be in the same BSS • Assuming STA have some form of spatial interference footprint information of STAs in BSS • STA potential make smart decisions on associating with BSS with less interfering MU-MIMO STAs Daewon Lee, LG Electronics

  10. Discussion of STA spatial interference (1/2) • In small indoor environment signal Angular Spread (AS) is typically high (as shown in reference [1][2]) • this does not necessary mean in MU-MIMO transmission, the spatial interference between STAs are identical regardless of STA pairing • high AS typically means AP is required to apply frequency selective beamforming (precoding) to spatially separate interference between STAs • certain spatial interference correlation still may exist depending on what kind of beamforming mechanism is deployed at the AP Daewon Lee, LG Electronics

  11. Discussion of STA spatial interference (2/2) • In large spaced indoor environments (e.g. auditoriums) or outdoor environments • smaller AS compared to indoor environments and stronger spatial interference depending on physical locations of STAs • Although small indoor environments are important, we recommend 11ac to also support other deployment scenarios • note support does not necessary mean critically optimized, but we should strive to insure it does work well Daewon Lee, LG Electronics

  12. 802.11 BSS Load Element [3] • BSS load element contains ‘Channel Utilization’ • Channel Utilization = Integer((channel_busy_time/(dot11ChannelUtilizationBeaconIntervals × dot11BeaconPeriod × 1024)) × 255) • “channel_busy_time” is defined by CS busy time within the measurement window • No consideration of actual system capacity of MIMO-capable APs Daewon Lee, LG Electronics

  13. Issues with 11n BSS load element • Channel Utilization metric • does not take into account additional resource dimensionality the MU-MIMO capable AP has • resource dimensions { time, frequency, space } • does not take into account any potential spatial interference footprint between potential STAs • Station Count • does not distinguish STAs with MU-MIMO support Daewon Lee, LG Electronics

  14. Summary • General observations • 802.11 BSS load element does not seem to adequately take into account particulars of MU-MIMO operation • BSS load balancing in MU-MIMO environment are especially important since MU-MIMO benefits high data rate transmissions and large number of active STA • Better mechanisms supporting MU-MIMO supported environments seems necessary • Potential solution is to introduce a new control element for MU-MIMO supported STA association • details and exact mechanism needs further study Daewon Lee, LG Electronics

  15. Strawpoll ADD TEXT HERE!!!1 Daewon Lee, LG Electronics

  16. References [1] Greg Breit, Nachiket Desai, “Multi-User AoD Diversity Measurements,” IEEE 802.11-09/0699r0 [2] Kwak, B.-J. et al., “Measured Channel Capacity and AoD Estimation for Multi-User MIMO Scenarios,” IEEE 802.11-09/0543r0 [3] “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”, IEEE802.11-2007 Daewon Lee, LG Electronics

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