1. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 1 Comparison of 20/40 MHz coexistence methods 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, 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 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.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfstuart.kerry@philips.compatcom@ieee.org Date: 2005-01-15 Authors:

2. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 2 Abstract Simulation results are provided to compare the proposed 20/40 MHz coexistence methods. Results show the effectiveness of the TGn Sync 20 MHz-base method.

3. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 3 40 / 20 MHz coexistence When 40 MHz HT STAs coexist with 20 MHz legacy/HT STAs, there may be occasions when the HT AP has 20MHz legacy STAs operating on both 20MHz channels. Unmanaged CSMA/CA operated across the entire 40MHz has these issues: –While waiting the other channel to be idle, a 20 MHz STA may start to use the channel which was idle. –To acquire both channels at HT STAs, contention probability will increase to double. There are three solutions to this: –Operate in base-20 managed mixed mode –Select a new 40MHz channel location –Operate the BSS in a 20MHz channel This presentation compares the performance of the base-20 managed mixed mode with CSMA/CA operated across both 20 MHz channels.

4. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 4 Approach for 20-base managed mixed mode proposal The goal is to reduce the probability of 20MHz legacy/HT STAs and 40MHz STAs contending for the medium simultaneously. Some kind of mechanism needed to prevent 20 MHz legacy/HT STAs from transmitting by the HT AP when using 40 MHz channel. Coexistence with the existing 20 MHz legacy STAs is a must, especially in the transition period from 11a to 40 MHz 11n.

5. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 5 TGn Sync 20 MHz-base managed mixed mode operation AP sets NAV in both control and extension channels. –40MHz duration is created after the NAV setting in both channels. ch_a (control) CTS self /Bcn CF- End t ch_b (extension) Bcn/ ICB CF- End CF- End t DCB NAV ch_a NAV ch_b 20MHz 40MHz Carrier Sense (CS) CS Busy NAV ch_a+ch_b

6. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 6 WWiSE Operation A STA that wishes to transmit a frame on both channels of 40MHz shall conduct CCA on both the primary and the secondary channels. –Frame is transmitted on both channels of 40MHz if both channels are idle. –Frame is transmitted on the primary channel if only the primary channel is idle. ch_a (primary) t ch_b (secondary) t NAV ch_a NAV ch_b CS NAV Frame Exchange (20MHz) Busy 20/40 switching time may be required. Unclear, so not covered this behaviour in the simulation. CS Frame Exchange (40MHz) CS NAV ch_a+ch_b CS Carrier Sense (CS)

7. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 7 Pros and cons analysis of the methods Overhead to get 40MHz channel 40 MHz Tx basisContention with 20 MHz STAs in the extension channel Contention for 40 MHz transmission TGn Sync 20 MHz- base - Large Channel switching time and NAV setting in both channels required. - Can provide sequential TXOPs (CAPs) without access overhead. - Low probability Because HT AP takes care most of the part at the start of the 40 MHz period. - Low probability Due to access limited to 40 MHz HT STAs. WWiSE - Small Channel switching may occur under some conditions. - Need to access for each 40 MHz TXOP. - High probability Each 40 MHz STA including the HT AP has to contend. - High probability Due to contention needed in two channels. Blue writing represents advantage.

8. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 8 Performance comparison --- Simulation Parameters --- Number of nodes in target BSS : Na2 or 4 (including 1 AP) Number of nodes in legacy OBSS : Nb2 or 4 for (1), Varied for (2) (including 1 AP) Load on 40 MHz node50 Mbps Load on legacy 20 MHz node in OBSS5 Mbps for (1), 2 Mbps for (2) Beacon interval100 ms Number of aggregated frames16 MPDU size1500 bytes Transmission rate in 40 MHz216 Mbps Transmission rate in 20 MHz (for Beacon, control frames for 20-base, and OBSS) 54 Mbps Channel switching time (TGn Sync)1 ms CWmin15 AIFSSIFS + 3*slottime Maximum retry count4 Position of nodesVaried based on range of AP-STAs

9. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 9 Network topology for case (1): Throughput/Collision Rate vs. Distance between OBSS --- Na=2, Nb=2 or 4 --- 40MHz in ch_a 20MHz in ch_b 40MHz AP in BSS 1 [m] BSS by 40MHz AP (using ch_a for 20MHz transmission, ch_a & ch_b for 40MHz transmission) OBSS by 20MHz AP (using ch_b) 20MHz AP in OBSS 1 [m] 40MHz STA in BSS20MHz STA in OBSS d [m] d : varied (5-70 [m]) 40MHz commun. No. of nodes (Na) = 2 20MHz commun. in ch_b -> interference to 40MHz commun. No. of nodes (Nb) = 2 For Nb=4 case, 2 more STAs are added at regular intervals

10. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 10 Performance comparison (1) Throughput/Collision Rate vs. Distance between OBSS Coverage is smaller in 40 MHz -> more probability of STAs within/outside BSS not setting NAV by WWiSE method -> more probability of collision from 20MHz-STAs in the extension channel Throughput in 40MHz vs. Range of AP-STAsCollision rate vs. Range of AP-STAs

11. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 11 Network topology for case (2): Throughput/Collision rate vs. Number of OBSS nodes --- Na=4(fixed), Nb=0-24(varied) --- 40MHz AP BSS by 40MHz AP OBSS by 20MHz AP 20MHz AP in ch_b 1 [m] 20MHz STA in ch_b 20 [m] 40MHz commun. No. of nodes (Na) = 4 40MHz STA 20MHz commun. in ch_b -> interference to 40MHz commun. No. of nodes (Nb) = 0-24 1 [m]...

12. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 12 Performance comparison (2) Throughput/Collision rate vs. Number of OBSS nodes (Number of nodes in the target BSS=4) In WWiSE spec, prohibiting the usage of the extension channel cannot be perfect. -> Collision increases as the number of STAs in the extension channel increases. Throughput in 40MHz vs. Number of OBSS nodes Collision rate vs. Number of OBSS nodes

13. doc.: IEEE 802.11-05/1633r0 Submission January 2005 Tomoko Adachi, Toshiba CorporationSlide 13 Summary TGn Sync 20 MHz-base method lowers the probability of collision with 20 MHz STAs in the extension channel resulting in higher throughput in 40MHz communication compared with the WWiSE method. TGn Sync 20 MHz-base method is more effective, –When OBSS exists on the extension channel, especially when it has large number of STAs. –When STAs in the extension channel are locating where CCA can be detected for 20 MHz but cannot for 40 MHz.