1、January 2005,Tomoko Adachi, Toshiba Corporation,Slide 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 doc
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7、 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 .,Date: 2005-01-15,Authors:,January 2005,Tomoko Adachi, Toshiba Corporation,Slide 2,Abstract,Simulation res
8、ults are provided to compare the proposed 20/40 MHz coexistence methods. Results show the effectiveness of the TGn Sync 20 MHz-base method.,January 2005,Tomoko Adachi, Toshiba Corporation,Slide 3,40 / 20 MHz coexistence,When 40 MHz HT STAs coexist with 20 MHz legacy/HT STAs, there may be occasions w
9、hen 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
10、will increase to double. There are three solutions to this:Operate in base-20 managed mixed modeSelect a new 40MHz channel locationOperate the BSS in a 20MHz channelThis presentation compares the performance of the base-20 managed mixed mode with CSMA/CA operated across both 20 MHz channels.,January
11、 2005,Tomoko Adachi, Toshiba Corporation,Slide 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
12、 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.,January 2005,Tomoko Adachi, Toshiba Corporation,Slide 5,TGn Sync 20 MHz-base managed mixed mode operation,AP sets NAV in both control and exten
13、sion channels.40MHz duration is created after the NAV setting in both channels.,ch_a (control),CTSself/Bcn,CF-End,t,ch_b (extension),Bcn/ICB,CF-End,CF-End,t,DCB,NAV,NAV,NAVch_a,NAVch_b,20MHz,40MHz,CarrierSense(CS),CS,CS,Busy,NAV,NAV,NAVch_a+ch_b,January 2005,Tomoko Adachi, Toshiba Corporation,Slide
14、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.
15、,ch_a (primary),t,ch_b (secondary),t,NAVch_a,NAVch_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,CS,NAV,NAVch_a+ch_b,CS,CarrierSense(CS),January 2005,Tomoko Adachi, Toshiba Corporation,S
16、lide 7,Pros and cons analysis of the methods,Blue writing represents advantage.,January 2005,Tomoko Adachi, Toshiba Corporation,Slide 8,Performance comparison - Simulation Parameters -,January 2005,Tomoko Adachi, Toshiba Corporation,Slide 9,Network topologyfor case (1): Throughput/Collision Rate vs.
17、 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 BSS,20MHz STA in OBSS,d m,d : varied (5-70 m),40MHz commu
18、n.No. of nodes (Na) = 2,20MHz commun. in ch_b - interference to 40MHz commun.No. of nodes (Nb) = 2For Nb=4 case, 2 more STAs are added at regular intervals,January 2005,Tomoko Adachi, Toshiba Corporation,Slide 10,Performance comparison(1) Throughput/Collision Rate vs. Distance between OBSS,Coverage
19、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-STAs,Collision rate vs. Range of AP-STAs,January 2005,Tomoko Adachi, Toshiba Corporation,Slide
20、 11,Network topologyfor 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 commu
21、n.No. of nodes (Nb) = 0-24,1 m,1 m,1 m,1 m,.,January 2005,Tomoko Adachi, Toshiba Corporation,Slide 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.- Co
22、llision 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,January 2005,Tomoko Adachi, Toshiba Corporation,Slide 13,Summary,TGn Sync 20 MHz-base method lowers the probability of collision with 20 MH
23、z 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.,
