Long SlotTime Option for RTS/CTS Procedure May 2007 Long SlotTime Option for RTS/CTS Procedure Date: 2007-05-15 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.kerry@philips.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>. Y. Inoue & K.Kawamura (NTT)

May 2007 Abstract This submission contains a proposal called Long SlotTime option for RTS/CTS procedure which is simple modification of legacy RTS/CTS handshake to be effective in the outdoor deployments. Y. Inoue & K.Kawamura (NTT)

May 2007 Rationale 802.11y systems will be widely deployed in outdoor environments There will be more opportunity to see the “hidden station problem” Although RTS/CTS procedure is defined in the base standard to minimize the effect of hidden station problem, some problems are still remained. This proposal provides a solution for the issue in current RTS/CTS procedure Y. Inoue & K.Kawamura (NTT)

Issue in current RTS/CTS Procedure May 2007 Issue in current RTS/CTS Procedure DIFS/ AIFS RTS STA#1 Collision! hidden AP RTS SlotTime STA#2 Hidden STA could start its transmission even when another station is sending the RTS to the AP This is because SlotTime is shorter than the RTS frame duration Y. Inoue & K.Kawamura (NTT)

Solution: Long SlotTime Option May 2007 Solution: Long SlotTime Option DIFS/ AIFS RTS STA#1 hidden CTS AP SIFS NAV LongSlotTime STA#2 Use LongSlotTime for the RTS transmission can minimize the collision probability of RTS frames Y. Inoue & K.Kawamura (NTT)

LongSlotTime: How long should it be? May 2007 LongSlotTime: How long should it be? A station may not realize that a hidden node started a transmission of RTS frame until it receives CTS frame  LongSlotTime should be LongSlotTime >= TRTS_Duration + SIFS + a where a is the time to detect a frame. Y. Inoue & K.Kawamura (NTT)

May 2007 Pros and Cons Pros. LongSlotTime option effectively minimizes the collision probability of RTS frames from different stations. Cons. Increased overhead. Y. Inoue & K.Kawamura (NTT)

Some Results Prob. Successful Transmission [%] May 2007 100 80 60 40 CW = 127 CW = 1023 60 LongSlotTime Option Prob. Successful Transmission [%] Legacy RTS Transmission 40 20 CW = 15 5 10 15 20 25 30 Number of STAs Y. Inoue & K.Kawamura (NTT)

May 2007 Maximum Throughput (1) All frames are assumed to be sent using 6M bit/s mode. Long SlotTime: 72 [us] Since the SlotTime for RTS transmission is increased, maximum throughput will be decreased. Y. Inoue & K.Kawamura (NTT)

Maximum Throughput (2) Similar calculation with the previous page. May 2007 Maximum Throughput (2) Similar calculation with the previous page. Data & ACK: 24M bit/s RTS & CTS: 6M bit/s Long SlotTime: 72 [us] Y. Inoue & K.Kawamura (NTT)

Simulation Result Maximum throughput is also decreased by collision. May 2007 Simulation Result Maximum throughput is also decreased by collision. 2 4 6 8 10 12 14 16 18 20 Offered Traffic [M bit/s] Throughput [M bit/s] w/ Long SlotTime Option w/o Long SlotTime Option Data Rate = 24M bit/s Coverage Class = 0 Better throughput performance will be expected when the Long SlotTime option is used. Y. Inoue & K.Kawamura (NTT)

May 2007 Summary Use of LongSlotTime in transmitting RTS frames minimizes the collision probability of RTS frames in the hidden station scenarios. 802.11y should provide this option for the purpose of outdoor deployment. Y. Inoue & K.Kawamura (NTT)

May 2007 Questions? Y. Inoue & K.Kawamura (NTT)

May 2007 Straw Poll How many people would like to see the LongSlotTime Option in the next version of IEEE 802.11y draft? Yes: No: Abstain: Y. Inoue & K.Kawamura (NTT)

May 2007 Motion Y. Inoue & K.Kawamura (NTT)