Analysis on IEEE 802.11n MAC Efficiency Month Year doc.: IEEE 802.11-yy/xxxxr0 September 2007 Analysis on IEEE 802.11n MAC Efficiency Date: 2007/09/13 Authors: 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>. Minyoung Park, Intel Corp. John Doe, Some Company

Month Year doc.: IEEE 802.11-yy/xxxxr0 September 2007 Abstract This analysis is to understand how efficient current IEEE 802.11n MAC protocol is when used for PHY rate of 1Gbps and beyond, and to understand what the challenges are to achieve over 1Gbps MAC throughput with current technology. Minyoung Park, Intel Corp. John Doe, Some Company

Contention Window (CW) September 2007 802.11n MAC Protocol Improving MAC efficiency Contention Window (CW) pr RTS pr CTS pr DATA pr ACK DIFS SIFS SIFS SIFS preamble CW pr RTS pr CTS pr DATA pr ACK DIFS SIFS SIFS SIFS Block Ack CW pr RTS pr CTS pr DATA … DATA pr BA DIFS SIFS SIFS SIFS CW pr RTS pr CTS pr DATA … DATA pr BA DIFS SIFS SIFS SIFS pr DATA … DATA pr BA SIFS SIFS Minyoung Park, Intel Corp.

802.11n MAC Overhead and Efficiency September 2007 802.11n MAC Overhead and Efficiency TXOP up to 64 subframes CW (variable) Actual data Actual data pr RTS SIFS pr A-MPDU SIFS pr A-MPDU SIFS DIFS pr CTS SIFS pr BA SIFS pr BA overhead overhead overhead Total MAC payload (bits) MAC throughput = Time consumed transmitting total MAC payload (sec) MAC throughput MAC efficiency = PHY rate MAC efficiency increases as TXOP fixed overhead (e.g. DIFS and SIFS) Number of BAs aggregation overhead CW (or # of stations) contention overhead Minyoung Park, Intel Corp.

MAC Throughput with Contention September 2007 MAC Throughput with Contention Collision overhead TXOP CWmax doubled CW=4 CW=2 CW=8 STA-A RTS RTS SIFS RTS SIFS SIFS A-MPDU SIFS DIFS DIFS CTS DIFS CTS SIFS BA freeze CWmax doubled CW=2 CW=10 STA-B CW=2 RTS SIFS A-MPDU SIFS RTS SIFS RTS DIFS CTS SIFS BA DIFS CTS DIFS freeze Aggregate throughput: STA-A + STA-B overhead Actual data Collision overhead overhead Actual data overhead CW=8 CW=2 RTS SIFS A-MPDU SIFS RTS SIFS RTS SIFS SIFS A-MPDU SIFS DIFS CTS SIFS BA DIFS CTS DIFS CTS SIFS BA When there is no collision between the stations, the station with the smallest CW will access the channel and thus CW overhead gets smaller as the number of stations increases Overhead due to collision is shared by all the stations in the network Minyoung Park, Intel Corp.

CSMA/CA Contention Overhead Analysis September 2007 CSMA/CA Contention Overhead Analysis Minimum overhead Contention overhead = CW overhead + collision overhead CW overhead decreases as # of STAs increases  STA with smallest CW will access the channel Collision overhead increases as # of STAs increases Minyoung Park, Intel Corp.

802.11n MAC Throughput (Single STA) September 2007 802.11n MAC Throughput (Single STA) HT 4x4 320MHz TXOP=1, 2, 3ms HT 4x4 160MHz TXOP=1, 2, 3ms 1Gbps MAC throughput HT 4x4 80MHz TXOP=1, 2, 3ms HT 4x4 120MHz TXOP=1, 2, 3ms BER=1e-5 CW=15 Packet size =1500 Bytes For 4x4 MIMO, 802.11n needs at least >160MHz bandwidth and large TXOP (>1ms) Minyoung Park, Intel Corp.

802.11n MAC Efficiency (Single STA) Month Year doc.: IEEE 802.11-yy/xxxxr0 September 2007 802.11n MAC Efficiency (Single STA) HT 4x4 80MHz HT 4x4 160MHz HT 4x4 320MHz HT 4x4 120MHz BER=1e-5 CW=15 Packet size =1500 Bytes Efficiency decreases below 50% as PHY rate increases over 3Gbps Minyoung Park, Intel Corp. John Doe, Some Company

802.11n MAC Throughput and Efficiency (Multiple STAs) September 2007 802.11n MAC Throughput and Efficiency (Multiple STAs) Throughput Efficiency PHY rate Target MAC throughput 802.11n BER=1e-5 Packet size = 1500 Bytes TXOP=3ms Number of STAs: 1~50 Current 802.11n requires 2Gbps PHY rate to achieve >1Gbps MAC throughput Minyoung Park, Intel Corp.

MAC Overhead Analysis September 2007 5 STAs (TXOP=3ms) Varying PHY rate 1040 Mbps (e.g. 4x4 80MHz, TXOP=3ms) Varying number of STAs As PHY rate increases, aggregation overhead increases For a small number of STAs (PHY rate > 1Gbps) aggregation overhead dominates For a large number of STAs (PHY rate > 1Gbps) contention overhead + aggregation overhead dominates Minyoung Park, Intel Corp.

September 2007 Conclusions The approach to extend 802.11n for PHY rate > 1Gbps has MAC efficiency problem MAC efficiency is ~64% for PHY rate ≈ 1Gbps (5 STAs, TXOP=3ms) MAC efficiency is ~40% as PHY rate increases to 4Gbps Contention and aggregation overheads dominate the overall overhead 802.11n needs at least 160MHz BW for 4x4 MIMO to reach 1Gbps MAC throughput Evolution from 802.11n requires higher spectral and MAC efficiency, for example: PHY rate = 1.3Gbps @ 80MHz BW MAC efficiency = 80% Performance metric recommended for VHT Aggregate network throughput (instead of point-to-point throughput) Minyoung Park, Intel Corp.