Another resource to exploit: multi-user diversity May 2007 doc.: IEEE 802.11-07/2187r0 July 2007 Another resource to exploit: multi-user diversity Authors: Date: 2007-07-17 Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair stuart@ok-brit.com as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>. Marc de Courville (Motorola) Marc de Courville (Motorola)

Motivation for 11vht multi band evolution July 2007 Motivation for 11vht multi band evolution Reality of the market: Wi-Fi penetration in the home/enterprise/outdoor is growing Need to face diversity of device classes and features in a robust way Need to support multiple connections: throughput shouldn’t drop when increasing the number of devices (in the home simultaneous support for IPTV/MP3 streaming & VoIP calls is a reality) All the more true for public access networks and office/enterprise communication solutions Core questions: How to support various BW devices without too much overhead? Is there a value to have several devices transmitting at the same time? OFDMA exists and provides solutions to: Unbalanced link budgets Improved spectral efficiency/higher capacity through more optimal resource scheduling Dynamic adaptive bandwidth enables spectrum allocation to be sized to traffic need Marc de Courville (Motorola)

Padding loss: it increases with the bandwidth! July 2007 Padding loss: it increases with the bandwidth! Fact: when increasing the bandwidth the OFDM granularity becomes quite large and even larger with MIMO to accommodate various packet sizes resulting in increased padding inefficiencies! Average: bit per carrier considering coverage of MCSs (SISO TGnD, 5% PER): around 1.47bit/carrier Padding loss on the useful message versus bandwidth utilization: 1.7dB (average) and up to 2.2dB for VoIP packet (ACELP AMR codec at 12.2kbps, 20ms sampling; counting RTP+UDP+IP=40B header and 11 MAC header=34B) Conclusion: with increased granularity we can gain some dBs… Marc de Courville (Motorola)

Materializing multi-user diversity gain July 2007 Materializing multi-user diversity gain In order to increase granularity let assume several STAs are allowed to transmit at the same time with an orthogonal divisions of subcarriers (OFDMA). Goal: determine upper bound provided by frequency selective scheduling a.k.a. multi-user diversity gain Assumptions: OFDMA, frequency multiplexing of the users SISO TGnD channel TRMS=50ns, coherent bandwidth Bc=20MHz thus as a rule of thumb channel is almost constant over 12 consecutive subcarriers (Bc/5). Same carrier spacing as for 20MHz is assumed: 312.5kHz 100MHz bandwidth representing 320 subcarriers 8 adjacent subcarriers are grouped into one chunk Nu users are present: 320/Nu/8 chunks are allocated to each user Chunks are chosen so as to maximize the sum rate capacity Acronyms: OCA: optimized chunk allocation RCA: random chunk allocation Marc de Courville (Motorola)

PHY over the air throughput July 2007 PHY over the air throughput 6 users: 66% rate increase 2 users: 33% rate increase Marc de Courville (Motorola)

Equivalent SNR Gain of OCA vs. RCA function of SNR July 2007 Equivalent SNR Gain of OCA vs. RCA function of SNR >2dB gain already with 2 users! Marc de Courville (Motorola)

PHY Rate CDF July 2007 ~50Mbps >75Mbps ~50Mbps Marc de Courville (Motorola)

Some conclusions on the simulations and implications July 2007 Some conclusions on the simulations and implications Simulation results: BTW OCA represents also a one user full bandwidth usage Multi-User diversity gain starts with a 2dB for 2 users served and reaches 5dB for 6 users In terms of throughput benefit: at 10dB SNR, 33% gain with 2 users and 66% gain with 6 users Marc de Courville (Motorola)

Next steps and challenges July 2007 Next steps and challenges Thoughts on link budget: is the OFDMA power boost required? AP 1W limitation (30dBm: 5GHz upper band), STA 200mW (SAR regulation 23dBm) DL: 100MHz (5x20MHz) yields same power spectral density as for 200mW 20MHz transmissions UL: 200mW limitation for STA indicates an unbalanced link budget that can be compensated with OFDMA serving 5 users increasing the energy per subcarrier by a factor of 5 Challenge: this presentation deals only with a potential PHY gain to be materialized by dedicated MAC protocols Open questions: What are the required ingredients to feed the PAR that will allow to capitalize on this new source of diversity? Can OFDMA be coupled with smart interference management to handle overlapping BSS for efficient deployments? From SISO to MIMO: does the frequency selective scheduling gain remain due to the “implicit antenna averaging”? It might depend on the MIMO mode. Conclusion: Multi-user diversity is a resource not exploited by IEEE802.11n OFDMA is a proven technology already present in IEEE802.16, 3GPP LTE is now investigating Multi-User MIMO (e.g. PU2RC). IEEE802.11vht should take these existing and new trends into consideration in the PAR and in the specification drafting process. Marc de Courville (Motorola)

Backup: influence of the chunk size July 2007 Backup: influence of the chunk size Context: comparison with chunks of size 4, 8, 32 Slight improvement with smaller chunks but 10 chunks of 32 carriers would require less MAC overhead Marc de Courville (Motorola)