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Doc.: IEEE 802.11-10/0783r0 Submission July 2010 Daewon Lee, LG ElectronicsSlide 1 MU-MIMO support for BSS load balancing Date: 2010-07-13 Authors:

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1 doc.: IEEE /0783r0 Submission July 2010 Daewon Lee, LG ElectronicsSlide 1 MU-MIMO support for BSS load balancing Date: Authors:

2 doc.: IEEE /0783r0 Submission July 2010 Daewon Lee, LG ElectronicsSlide 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.

3 doc.: IEEE /0783r0 Submission 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 July 2010 Daewon Lee, LG ElectronicsSlide 3

4 doc.: IEEE /0783r0 Submission 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? July 2010 Daewon Lee, LG ElectronicsSlide 4

5 doc.: IEEE /0783r0 Submission 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 July 2010 Daewon Lee, LG ElectronicsSlide 5

6 doc.: IEEE /0783r0 Submission 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 July 2010 Daewon Lee, LG ElectronicsSlide 6

7 doc.: IEEE /0783r0 Submission 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 July 2010 Daewon Lee, LG ElectronicsSlide 7

8 doc.: IEEE /0783r0 Submission 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 July 2010 Daewon Lee, LG ElectronicsSlide 8

9 doc.: IEEE /0783r0 Submission 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 July 2010 Daewon Lee, LG ElectronicsSlide 9

10 doc.: IEEE /0783r0 Submission 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 July 2010 Daewon Lee, LG ElectronicsSlide 10

11 doc.: IEEE /0783r0 Submission 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 July 2010 Daewon Lee, LG ElectronicsSlide 11

12 doc.: IEEE /0783r0 Submission BSS Load Element [3] BSS load element contains ‘Channel Utilization’ –Channel Utilization = Integer((channel_busy_time/(dot11ChannelUtilizationBeaconInter vals × 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 July 2010 Daewon Lee, LG ElectronicsSlide 12

13 doc.: IEEE /0783r0 Submission 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 July 2010 Daewon Lee, LG ElectronicsSlide 13

14 doc.: IEEE /0783r0 Submission Summary General observations – 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 July 2010 Daewon Lee, LG ElectronicsSlide 14

15 doc.: IEEE /0783r0 Submission Strawpoll July 2010 Daewon Lee, LG ElectronicsSlide 15 ADD TEXT HERE!!!1

16 doc.: IEEE /0783r0 Submission References [1] Greg Breit, Nachiket Desai, “Multi-User AoD Diversity Measurements,” IEEE /0699r0 [2] Kwak, B.-J. et al., “Measured Channel Capacity and AoD Estimation for Multi-User MIMO Scenarios,” IEEE /0543r0 [3] “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”, IEEE July 2010 Daewon Lee, LG ElectronicsSlide 16


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