[SDMA operation within 802.11]

[SDMA operation within 802.11] Authors: Date: 2009-05-09 Yuichi Morioka, Sony Corporation

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

SDMA Technology for 802.11 • 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 SDMA Operation Yuichi Morioka, Sony Corporation

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

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] • 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) Example SDMA Sequence Effect of OBSS Yuichi Morioka, Sony Corporation

Legacy Interoperability for SDMA [2/3] • 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 Example Frame Structure 1 Example Frame Structure 2 Example Frame Structure 3 Legacy Location Yuichi Morioka, Sony Corporation

Legacy Interoperability for SDMA [3/3] • 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 Legacy Location SIFS Variability Yuichi Morioka, Sony Corporation

OBSS Scenarios in 802.11 • 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 STA1 STA2 STA1 AP1 AP2 AP1 AP2 OBSS Case 1 OBSS Case 2 Yuichi Morioka, Sony Corporation

OBSS Coordination [1/2] • 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 Two Neighboring BSS Example Sequence Yuichi Morioka, Sony Corporation

OBSS Coordination [2/2] • 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 Sounding Frame Structure Yuichi Morioka, Sony Corporation

Packet Size Adjustment[1/2] • 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 Mismatch of Packet Size Padding/Training Yuichi Morioka, Sony Corporation

Packet Size Adjustment[1/2] • 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 Mismatch of Packet Size Multi-User Aggregation Yuichi Morioka, Sony Corporation

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 Uplink SDMA Yuichi Morioka, Sony Corporation

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

Thank you! Yuichi Morioka, Sony Corporation

[SDMA operation within 802.11]