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MU-MIMO STA scheduling strategy and Related PHY signaling

MU-MIMO STA scheduling strategy and Related PHY signaling. Date: 2010-03-15. Authors:. 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

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MU-MIMO STA scheduling strategy and Related PHY signaling

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  1. MU-MIMO STA scheduling strategy and Related PHY signaling Date: 2010-03-15 Authors: Daewon Lee, LG Electronics

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

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

  11. Properties ofSpatial 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

  12. Comparison ofSS 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 Daewon Lee, LG Electronics

  13. 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

  14. Straw Poll 1 • Considering environments which MU-MIMO may have outstanding performances, do you agree to have further investigation on the grouping concept for MU-MIMO STA co-scheduling? • Yes • No • Abstain Daewon Lee, LG Electronics

  15. Straw Poll 2 • Do you support adding the Spatial Stream Configuration Index (SSCI) field to VHT-SIG as described in 10/0362r0 and similar in 10/0073r3, and editing the spec framework document, 11-09-0992, accordingly? • Yes • No • Abstain Daewon Lee, LG Electronics

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