1. [SDMA operation within 802.11]
May 2009
doc.: IEEE /0532r0
May 2009
[SDMA operation within ]
Date:
Authors:
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

2. Abstract SDMA = Promising technology for the evolution of 802.11
May 2009
doc.: IEEE /0532r0
May 2009
Abstract
SDMA = Promising technology for the evolution of
Points to consider when deploying SDMA in arena
Un-coordinated neighboring networks
Un-coordinated traffic flow
Some techniques to mitigate these issues are introduced
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

3. May 2009
doc.: IEEE /0532r0
May 2009
SDMA Technology for
SDMA Operation
With the vast deployment of .11 technology, SDMA that allows for multiple simultaneous links, is a natural course of evolution for .11
As the number of .11 devices grow, we believe that the effect would become more prominent
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

4. Important characteristics of 802.11
May 2009
doc.: IEEE /0532r0
May 2009
Important characteristics of
The unlicensed nature of has allowed successive generations to interoperate with existing legacy installed base
Unlike cellular systems, coordination between BSS’s are not widely deployed in
has to serve many different application types and therefore typically specifies broad flexibility in packet size with each generation
Accommodates video, bulk data transfer, real-time audio, etc.
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

5. Related Topics Considered
May 2009
Related Topics Considered
Packet structure for SDMA that is decodable by Legacy
Strict time alignment of simultaneous packets
Loose OBSS coordination
SDMA PPDU size adjustment methods
Uplink SDMA
Uncoordinated Neighboring Networks
Yuichi Morioka, Sony Corporation

6. Legacy Interoperability for SDMA [1/3]
May 2009
doc.: IEEE /0532r0
May 2009
Legacy Interoperability for SDMA [1/3]
Example SDMA Sequence
Effect of OBSS
Legacy Interoperability has been the key factor in evolution of
If above sequence is assumed, TRQ and Sounding Frames need to be legacy interoperable
TRQ can be sent in legacy PPDU format
However, Sounding Frame has to contain a unique sequence for SDMA separation, so they can not be sent at legacy PPDU format
Also, a STA may overhear multiple simultaneous Sounding Frames sent from different STAs (e.g. blue X)
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

7. Legacy Interoperability for SDMA [2/3]
May 2009
doc.: IEEE /0532r0
May 2009
Legacy Interoperability for SDMA [2/3]
Example Frame Structure 1
Example Frame Structure 2
Example Frame Structure 3
Legacy Location
To convey NAV information with SDMA Sounding Frame, the front portion of the frame has to be legacy understandable
Structure 1: legacy compatible up to L-SIG, rely on PHY Level Spoofing
Structure 2: legacy compatible up to MAC Header, unique sequence immediately follow
Structure 3: entire PPDU compatible with legacy, unique sequence encoded with 90 degree shift of BPSK signal constellation
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

8. Legacy Interoperability for SDMA [3/3]
May 2009
doc.: IEEE /0532r0
May 2009
Legacy Interoperability for SDMA [3/3]
Legacy Location
SIFS Variability
Some STAs may hear multiple Sounding Frames from different STAs
In order for this legacy STA to be able to decode the frame, the frame has to be:
Identical in content, at least up to the part that convey NAV information
Received within at least guard interval, to interpret them as single frame from different paths
In ac, a more strict timing constraint may need to be in place
Perhaps a time adjustment mechanism using RTS/CTS, Data/ACK transaction may be beneficial
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

9. OBSS Scenarios in 802.11 May 2009 Two types of OBSS scenarios
doc.: IEEE /0532r0
May 2009
OBSS Scenarios in
STA1
STA1
STA2
AP1
AP2
AP1
AP2
OBSS Case 1
OBSS Case 2
Two types of OBSS scenarios
Case1: A STA in a BSS can over-hear the AP in the OBSS
Case2: A STA in a BSS can over-hear only the non-AP STA in the OBSS
Case 2 is more severe because;
Case 1 is easily avoidable, because the OBSS AP can hear the STA in the other BSS and select another channel to operate
More probably of case 2 because it involves a larger area
In order to mitigate problems caused by Case 2, packets sent by the “STA” must be recognized by the OBSS
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

10. OBSS Coordination [1/2] May 2009 SDMA operates under strict scheduling
doc.: IEEE /0532r0
May 2009
OBSS Coordination [1/2]
Two Neighboring BSS
Example Sequence
SDMA operates under strict scheduling
When two Neighboring BSSs both operate SDMA, it may be inefficient, causing collision
If some information can be given to the other BSS, it may be helpful
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

11. OBSS Coordination [2/2] May 2009
doc.: IEEE /0532r0
May 2009
OBSS Coordination [2/2]
Sounding Frame Structure
If the scheduling information is copied in the response frame, the information can be overheard by the OBSS
.11ac STA in the OBSS may pass the scheduling information to the OBSS .11ac AP
The conveyed information can be used to schedule SDMA in the OBSS, so collision is minimized
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

12. Packet Size Adjustment[1/2]
May 2009
doc.: IEEE /0532r0
May 2009
Packet Size Adjustment[1/2]
Mismatch of Packet Size
Padding/Training
Packet size to different STAs may vary in length
The unused “space” would be a waste, and would lower SDMA efficiency
One solution may be to use the “space ” for additional training to improve signal quality
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

13. Packet Size Adjustment[1/2]
May 2009
doc.: IEEE /0532r0
May 2009
Packet Size Adjustment[1/2]
Mismatch of Packet Size
Multi-User Aggregation
Multi-User Aggregation for packet size adjustment
This will improve transmission power per user
In above left, tx power per data receiver is ¼ the total tx power
In above right, tx power per data receiver is ½ the total tx power
Also use of different channel width per packet could be considered to adjust PPDU size
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

14. May 2009
doc.: IEEE /0532r0
May 2009
Uplink SDMA
Uplink SDMA
Uplink SDMA can be realized with RDG to further improve SDMA efficiency
By using the RDG mechanism introduced in n, uplink SDMA can be easily realized
Additional information in the RDG Field may be necessary to unify uplink packet size, in order to avoid drastic change in receive power at the AP
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

15. Conclusion SDMA = Promising technology for the evolution of 802.11
May 2009
doc.: IEEE /0532r0
May 2009
Conclusion
SDMA = Promising technology for the evolution of
Points to consider when deploying SDMA in arena
Un-coordinated neighboring networks
Un-coordinated traffic flow
Techniques to mitigate these issues were introduced
Legacy decodable SDMA packet structure
Time Alignment
Loose OBSS coordination
SDMA PPDU size adjustment methods
Uplink SDMA
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation

16. Thank you! May 2009 May 2009 doc.: IEEE 802.11-09/0532r0
Yuichi Morioka, Sony Corporation
Yuichi Morioka, Sony Corporation