[SDMA operation within 802.11] May 2009 doc.: IEEE 802.11-09/0532r0 May 2009 [SDMA operation within 802.11] Date: 2009-05-09 Authors: Yuichi Morioka, Sony Corporation Yuichi Morioka, Sony Corporation

Abstract SDMA = Promising technology for the evolution of 802.11 May 2009 doc.: IEEE 802.11-09/0532r0 May 2009 Abstract SDMA = Promising technology for the evolution of 802.11 Points to consider when deploying SDMA in 802.11 arena Un-coordinated neighboring 802.11 networks Un-coordinated 802.11 traffic flow Some techniques to mitigate these issues are introduced Yuichi Morioka, Sony Corporation Yuichi Morioka, Sony Corporation

May 2009 doc.: IEEE 802.11-09/0532r0 May 2009 SDMA Technology for 802.11 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

Important characteristics of 802.11 May 2009 doc.: IEEE 802.11-09/0532r0 May 2009 Important characteristics of 802.11 The unlicensed nature of 802.11 has allowed successive generations to interoperate with existing legacy installed base Unlike cellular systems, coordination between BSS’s are not widely deployed in 802.11 802.11 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

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

Legacy Interoperability for SDMA [1/3] May 2009 doc.: IEEE 802.11-09/0532r0 May 2009 Legacy Interoperability for SDMA [1/3] Example SDMA Sequence Effect of OBSS Legacy Interoperability has been the key factor in evolution of 802.11 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

Legacy Interoperability for SDMA [2/3] May 2009 doc.: IEEE 802.11-09/0532r0 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

Legacy Interoperability for SDMA [3/3] May 2009 doc.: IEEE 802.11-09/0532r0 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 802.11ac, 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

OBSS Scenarios in 802.11 May 2009 Two types of OBSS scenarios doc.: IEEE 802.11-09/0532r0 May 2009 OBSS Scenarios in 802.11 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

OBSS Coordination [1/2] May 2009 SDMA operates under strict scheduling doc.: IEEE 802.11-09/0532r0 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

OBSS Coordination [2/2] May 2009 doc.: IEEE 802.11-09/0532r0 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

Packet Size Adjustment[1/2] May 2009 doc.: IEEE 802.11-09/0532r0 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

Packet Size Adjustment[1/2] May 2009 doc.: IEEE 802.11-09/0532r0 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

May 2009 doc.: IEEE 802.11-09/0532r0 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 802.11n, 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

Conclusion SDMA = Promising technology for the evolution of 802.11 May 2009 doc.: IEEE 802.11-09/0532r0 May 2009 Conclusion SDMA = Promising technology for the evolution of 802.11 Points to consider when deploying SDMA in 802.11 arena Un-coordinated neighboring 802.11 networks Un-coordinated 802.11 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

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