1. Preamble design aspects for MU-MIMO support
Month Year
doc.: IEEE yy/xxxxr0
Preamble design aspects for MU-MIMO support
Date:
Authors:
Name
Company
Address
Phone
Yujin Noh
LG Electronics, Inc.
LG R&D Complex 533, Hogye-1dong, Dongan-Gu, Anyang-Shi, Kyungki-Do, , Korea
Daewon Lee
Yongho Seok
Bonghoe Kim
John Doe, Some Company

2. Accelerate Contribution
November 2009
Accelerate Contribution
Introduction
Preamble modes
VHT mixed mode
VHT green field mode
Outstanding issues in order to support MU-MIMO
General PLCP design principle for SU/MU-MIMO support
Over-lapping PLCP design or Non-over-lapping PLCP design
Introduction of scramble signal and steered sounding PPDU
Straw poll Questions
LG Electronics, Inc.

3. Accelerate Contribution
November 2009
Accelerate Contribution
Discussion Topics
General PLCP design principle for SU/MU-MIMO support
Over-lapping PLCP design
Introduction of potential issues with over-lapping design and methods to mitigate interference issues
Non-over-lapping PLCP design
LG Electronics, Inc.

4. Preamble Modes for consideration
VHT-Mixed Mode
To support VHT transmission in BSS with Legacy, HT and VHT stations
VHT-Green Field Mode
To support VHT transmission in BSS with only VHT stations

5. General concept on SU/MU-MIMO
SU-MIMO
MU-MIMO
Each STA can use all transmitted streams from its own AP
More than one STA can use partial spatial streams from one AP
* Note that number of spatial streams for each STA can be larger than 1

6. General PLCP frame format design issue
Separate design for SU/MU-MIMO
Optimization for SU-MIMO and MU-MIMO separately
Transmission of SU or MU PLCP frame format chosen by transmitter (e.g. AP)
For SU, simple extension of HT PLCP frame format (e.g. MCS, number of supported layers, etc)
For MU, optimized MU PLCP frame format design
Common PCLP frame format for both SU/MU-MIMO
PLCP frame designed (and optimized) for MU-MIMO
Consider SU-MIMO a subset of MU-MIMO operation

7. Accelerate Contribution
November 2009
Accelerate Contribution
Discussion Topics
General PLCP design principle for SU/MU-MIMO support
Over-lapping PLCP design
Introduction of potential issues with over-lapping design and methods to mitigate interference issues
Non-over-lapping PLCP design
LG Electronics, Inc.

8. PLCP frame format design Option 1 (1/3)
November 2009
Accelerate Contribution
PLCP frame format design Option 1 (1/3)
Overlapping PLCP format design
STA specific VHT-SIG fields
Pre-coding of VHT-SIG
Spatial multiplexing of VHT-SIG for different STAs
Insertion of VHT-STF prior to VHT-SIG due to pre-coding effects
Partial spatial stream channel estimation as baseline
Only estimate spatial stream of appropriate receive data streams
May only allow partial MMSE (or even MRC) at receiver side
Note: all STAs may estimate channel of entire transmitted spatial streams depending on VHT LTF and VHT-SIG designs and utilize full MMSE
LG Electronics, Inc.

9. PLCP frame format design Option 1 (2/3)
November 2009
Accelerate Contribution
PLCP frame format design Option 1 (2/3)
Conceptual example PLCP transmission for overlapping PLCP design
VHT-mixed mode
*Note : the example shown assumes STA1 with 3 spatial streams and STA2 with 2 spatial streams are MU-MIMO paired
LG Electronics, Inc.

10. PLCP frame format design Option 1 (3/3)
Conceptual example PLCP transmission for overlapping PLCP design
VHT GF mode
*Note : the example shown assumes STA1 with 3 spatial streams and STA2 with 2 spatial streams are MU-MIMO paired

11. Accelerate Contribution
November 2009
Accelerate Contribution
Discussion Topics
General PLCP design principle for SU/MU-MIMO support
Over-lapping PLCP design
Introduction of potential issues with over-lapping design and methods to mitigate interference issues
Non-over-lapping PLCP design
LG Electronics, Inc.

12. Potential issues with overlapping design (1/2)
Scatter-rich environments
In scatter-rich environments, imperfect pre-coding can cause spatial streams to interfere with each other
Interference can cause degradation in channel estimation, data demodulation performance loss, etc.

13. Potential issues with overlapping design (2/2)
Null-space deficient environments
STAs with large number of receive antennas increase the statistical probability of null-space deficiency between AP-STA
Zero Forcing or Block Diagonal beam-forming may not be possible when null-space is not available for certain STAs
Case 1-1
Case 1-2
Clear separation between Two STAs
STA1 suffering from interference from paired STA2

14. Steered Sounding PPDU
Partial channel sounding or virtualized channel sounding instead of full channel sounding
AP recognizes smaller number of Rx antenna for STA
restrict the subspace of STA in order to increase null-subspace between AP-STA

15. Stream Scrambling Scramble signals for each STA
Scrambling allows the possibility to suppress interference with scrambling processing gain

16. Accelerate Contribution
November 2009
Accelerate Contribution
Discussion Topics
General PLCP design principle for SU/MU-MIMO support
Over-lapping PLCP design
Introduction of potential issues with over-lapping design and methods to mitigate interference issues
Non-over-lapping PLCP design
LG Electronics, Inc.

17. PLCP frame format design Option 2 (1/3)
November 2009
Accelerate Contribution
PLCP frame format design Option 2 (1/3)
Non-overlapping PLCP format design
STA specific VHT-SIG fields
VHT-SIG transmitted in omni-directional transmission method (cyclic delay shifting across physical antenna)
No spatial multiplexing of VHT-SIG (single stream transmission)
spatial stream (virtual spatial layer) indication for each STA receiving data
All MU STA can estimate channel for all spatial layers
allow full MMSE equalization implementation at receiver side
LG Electronics, Inc.

18. PLCP frame format design Option 2 (2/3)
November 2009
Accelerate Contribution
PLCP frame format design Option 2 (2/3)
Conceptual example PLCP transmission for Non-overlapping PLCP design
VHT-Mixed mode
그림이 overlapping으로 바껴있음 -_-;
*Note : the example shown assumes STA1 with 3 spatial streams and STA2 with 2 spatial streams are MU-MIMO paired
LG Electronics, Inc.

19. PLCP frame format design Option 2 (3/3)
Conceptual example PLCP transmission for Non-overlapping PLCP design
VHT-GF mode
*Note : the example shown assumes STA1 with 3 spatial streams and STA2 with 2 spatial streams are MU-MIMO paired

20. Straw poll Questions
Q1) Single PLCP frame format for both SU/MU-MIMO ?
Yes No
Q2) Support of spatial multiplexing of STA specific VHT-SIG in order to reduce preamble overhead ?
Single stream transmission of VHT-SIG (conceptually non over-lapped design)
Multi-stream transmission of VHT-SIG (conceptually over-lapped design)