1. MU-MIMO STA scheduling strategy and Related PHY signaling
March 2009
doc.: IEEE /XXXXr0
doc.: IEEE yy/xxxxr0
March 2010
MU-MIMO STA scheduling strategy and Related PHY signaling
Date:
Authors:
Name
Affiliation
Address
Phone
Daewon Lee
LG Electronics
LG R&D Complex 533, Hogye-1dong, Dongan-Gu, Anyang-Shi, Kyungki-Do, , Korea
Yonho Seok
Yujin Noh
Daewon Lee, LG Electronics
Daewon Lee, LG Electronics

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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, , accordingly?
Yes No
Abstain
Daewon Lee, LG Electronics

15. 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