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TXOP Redundancy NAV Clear

TXOP Redundancy NAV Clear. Date: 2013-9-16. Authors:. Background. Figure 2. Figure 1. As in fig1 ， STA3 stays in the OBSS of BSS1 and BSS2, and AP1 will send MU-MIMO frame to STA1~STA3.

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TXOP Redundancy NAV Clear

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  1. TXOP Redundancy NAV Clear Date:2013-9-16 Authors:

  2. Background Figure 2 Figure 1 • As in fig1，STA3stays in the OBSS of BSS1 and BSS2, and AP1will send MU-MIMO frame to STA1~STA3. • As in fig2, BSS1 occupies 80M bandwidth and the primary20 channel is #1; and the primary20 channel of BSS2 is #2.

  3. Problem Description Figure 3 • The DL-MIMO exchange procedure as in fig3 • 1) AP1 competes for the channel and sends RTS to STA1~STA3. Then STA1~STA3 responds with CTS frame in the idle channel including the primary channel, #1, of BSS1. • 2) when the channel occupied by the CTS frame responded by STA3 covers the primary channel, #2, of BSS2, then the NAV of AP2 and STA4 will be set to the TXOP time of AP1。 • 3) Then AP1 decides the DL-MIMO sending according to the CTS responds of STA1~STA3. There are two cases that the NAV of AP2 and STA4 will not be efficient for the duration of the TXOP.

  4. Problem Descriptioncon. Figure 4 • Problem • Case I: As in fig4, when the NAV of AP2 and STA4 were set, however the MU-MIMO data were not sent in the primary channel,#2, of BSS2. • As in fig4. a)AP1 select the primary20 channel,#1, to send the MU-MIMO data. • As in fig4. b)Due to the useful bandwidth of STA3 is smaller than STA1 and STA2, AP1 only select STA1 and STA2 to send MU-MIMO data.

  5. Problem Descriptioncon. Figure 5 • Problem • Case II: As in fig5. The MU-MIMO exchange occupied the primary channel, #2, of BSS2. • When the TXOP of AP1 were long for the MU-MIMO data exchange, and AP1 will send CF-END frame to clear the NAV of STAs in BSS1. However, the NAV of AP2 and STA4 will not be clear by the CF-END frame.

  6. Solution • Case I • Due to AP2 and STA4 will not listen the frame exchange in their primary channel, the AP2 and STA4 will waiting for a Maximal Frame Exchange time, if they won’t listen anything, then they can clear their NAV. • Case II • AP will indicate the last frame of MU-MIMO exchange to STA1~STA3 • Then the BA sent by STA3 should indicate the last frame to AP2 and STA4. If the TXOP is long for MU-MIMO exchange, then AP2 and STA4 can clear their NAV. • BA modification: We can use one reserved bit in BA control field to indicate the last frame.

  7. Solution con. • However, due to the OBSS, the NAV of STA will be set by more than one STA. So the NAV clear should not affect other STAs’ frame exchange. • We propose to solve this problem • The STA will record two NAV value: longest NAV and second long NAV and the address of STA who set the NAV. • When the NAV set by STA3 is the longest NAV of AP2 and STA4, then they can reset the longest NAV by setting it to the value of second long NAV and the second long NAV won’t change. Otherwise, they will do nothing. • The value setting of the two NAVs. • 1, If the NAV set by one STA is longer than the longest NAV, then set the longest NAV to this value and record its address. And set the second long NAV to the value of origin longest NAV. • 2, If the NAV set by one STA is shorter than the longest NAV and longer than the second long NAV, then set the second long NAV to this value. • 3, Otherwise, do nothing.

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