MU-MIMO STA scheduling strategy and Related PHY signaling March 2009 doc.: IEEE 802.11-10/XXXXr0 doc.: IEEE 802.11-yy/xxxxr0 March 2010 MU-MIMO STA scheduling strategy and Related PHY signaling Date: 2010-03-15 Authors: Name Affiliation Address Phone email Daewon Lee LG Electronics LG R&D Complex 533, Hogye-1dong, Dongan-Gu, Anyang-Shi, Kyungki-Do, 431-749, Korea +82-31-450-7897 daewon.lee@lge.com Yonho Seok yonho.seok@lge.com Yujin Noh +82-31-450-1947 yujin.noh@lge.com Daewon Lee, LG Electronics Daewon Lee, LG Electronics

MU-MIMO Usage Scenarios (1/2) March 2010 MU-MIMO Usage Scenarios (1/2) Observations on Usage Scenarios In typical usage scenarios, SU-MIMO will perform better than MU-MIMO MU-MIMO will only out perform SU-MIMO in MU-MIMO favorable environments Operation for MU-MIMO should prioritize optimizations for MU-MIMO favorable environments Optimization for other environments should be secondary Daewon Lee, LG Electronics

MU-MIMO Usage Scenarios (2/2) March 2010 MU-MIMO Usage Scenarios (2/2) MU-MIMO favorable environments (combination of below) Correlated Tx antennas at AP (Low channel rank for single STA) Interference footprint of each STA in case of correlated Tx antenna is stable Large number of Tx at AP & Small number of Rx antennas at STA (increased interference null subspace) Large number of STAs within BSS (increased probability of low interfering STA grouping, and potential STA pairing) Channel State Information (CSI) feedback from all STAs with MU-MIMO capability CSI feedback for STA grouping purposes should be infrequent Typical Precoding/Beamforming CSI has longer coherent time compared to MCS coherent time Receiving CSI from multiple STAs in every MU-MIMO transmission instant results in significant management overhead Daewon Lee, LG Electronics

MU-MIMO STA grouping strategy (1/3) March 2010 MU-MIMO STA grouping strategy (1/3) STA grouping in no-strong spatial correlation between STAs No specific grouping of STAs is needed AP will perform link adaptation depending on which STAs are co-scheduled Unless QoS sensitive traffic needs MU-MIMO transmission, STAs can be (logically) grouped arbitrarily SU-MIMO transmission can be always used for STAs which need data transmission right away Daewon Lee, LG Electronics

MU-MIMO STA grouping strategy (2/3) March 2010 MU-MIMO STA grouping strategy (2/3) STA grouping in strong spatial correlation between STAs Grouping decision based on Spatial interference footprint/signature STAs with strong spatial interference are preferably grouped in the same group Grouping is only logical grouping, which does not require specification in standard Daewon Lee, LG Electronics

MU-MIMO STA grouping strategy (3/3) March 2010 MU-MIMO STA grouping strategy (3/3) STA grouping in strong spatial correlation between STAs AP decides on which STAs out of low co-interfering STA group depending on traffic, fairness, QoS, throughput (interference), etc Daewon Lee, LG Electronics

Proposed STA co-scheduling signaling March 2010 Proposed STA co-scheduling signaling AP signals Spatial Stream Configuration Indication (SSCI) in VHT-SIG SSCI field is a VHT-SIG SSCI denotes {# of columns of Qk (NSTS-K) for k=0,1,2,3,…}, where Qk is the steering matrix for user k column vector indication in document 10/0073 Each STA is assigned a Spatial Stream Paging Index (SSPI) (e.g. 0,1,2,3, …) SSPI can be assigned by AP through MAC signaling (e.g. management frames) To save protocol overhead, SSPI can initially have a default value for STAs (e.g. Association ID hashed value) SSPI denotes NSTS-K index in SSCI Daewon Lee, LG Electronics

March 2010 Transmission Reception Operations for Spatial Stream Paging Method (1/3) For a given MU-MIMO transmission all STAs try to decode columns of Qk (NSTS-K) using SSPI indicated by AP respectively Each STA only decodes a particular set of spatial streams governed by SS paging index (Single Decoding) Receive STA ambiguity solved at MAC layer (just as in 11a/b/g/n) SSPI configuration If two or more STAs with same SSPI needs MU-MIMO transmission SSPI re-configuration can take place configuration/re-configuration can be done through MAC signaling Daewon Lee, LG Electronics

March 2010 Transmission Reception Operations for Spatial Stream Paging Method (2/3) Allows dynamic selection of combination of STAs without need for additional signaling Only required information in VHT-SIG is Spatial Stream configuration information (e.g. number of SS for each SSPI) Daewon Lee, LG Electronics

March 2010 Transmission Reception Operations for Spatial Stream Paging Method (3/3) Conceptual STA receive state for SS Paging ID based approach Daewon Lee, LG Electronics

Properties of Spatial Stream Paging Method March 2010 Properties of Spatial Stream Paging Method Supported combinations of STA is dramatically increased by use of overhearing feature supported combinations of STA for MU-MIMO No STA is left un-grouped and All STAs is available for MU-MIMO transmission Efficient in following cases slowly changing CSI conditions large number of STAs small number of STAs (e.g. less than 4~8) Daewon Lee, LG Electronics

Comparison of SS Paging ID based and Group ID based (10/0073r0) March 2010 Comparison of SS Paging ID based and Group ID based (10/0073r0) Example of supported combinations of STAs Assume maximum 4 co-schedule STA for MU-MIMO (i.e. 4 SS Paging ID) Assume 4 bit VHT-SIG signaling for Group ID based : 16 comb. Supported Note : comparison assuming long term CSI is available for MU-MIMO capable STAs NSTA C( NSTA, N ) Supported Comb. For SS Paging ID based 7 35 8 70 16 9 126 24 10 210 36 11 330 54 12 495 81 13 715 108 14 1001 144 15 1365 192 1820 256 17 2380 320 18 3060 400 Daewon Lee, LG Electronics

March 2010 Conclusion MU-MIMO optimization support in MU-MIMO favorable environments is preferred slowly changing CSI (especially precoding/beamforming information) environments Large number of STAs Spatial Stream Configuration Indication (SSCI) in VHT-SIG is needed allows dynamic selection of STAs and number of SS for each STA Spatial Stream Paging Index (SSPI) configuration for MU-MIMO capable STA seems beneficial allows larger amount of STA combination pairing without any additional configuration management frame overhead Daewon Lee, LG Electronics

March 2010 Straw Poll 1 Do you support adding the Spatial Stream Configuration Index (SSCI) field to VHT-SIG as described in 10/0362r0, and editing the spec framework document, 11-09-0992, accordingly? Yes No Abstain Daewon Lee, LG Electronics

March 2010 Straw Poll 2 Do you support concept of Spatial Stream Paging as in 11-10/0362r0 ? Yes No Abstain Daewon Lee, LG Electronics