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Consideration s on MU-MIMO Protection in 11 ac

Consideration s on MU-MIMO Protection in 11 ac. Date: 2010-0 3 - 15. Authors:. Slide 1. Introduction. MU-MIMO is considered to be supported in 11ac for improving system performance 11ac devices should protect its transmission from legacy devices operating in 5GHz

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Consideration s on MU-MIMO Protection in 11 ac

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  1. Considerationson MU-MIMO Protection in11ac Date: 2010-03-15 Authors: Slide 1

  2. Introduction • MU-MIMO is considered to be supported in 11ac for improving system performance • 11ac devices should protect its transmission from legacy devices operating in 5GHz • Protection mechanism for MU-MIMO data transmission should be considered • It is necessary to start to consider possible mechanism for NAV distribution for MU-MIMO protection

  3. Downlink MU-MIMO functions • General Downlink MU-MIMO functions • Sounding • Group control schemes • NAV distribution  Scope of this contribution • Beamformed data transmissions • Response phase

  4. NAV distribution for legacy protection • It is necessary to distribute NAV information to reserve the medium for a transmission of a nonbasic rate frame • Using RTS/CTS exchange • The exchange of RTS and CTS frames prior to the actual data frame is one means of distribution of this medium reservation information • Using CTS-to-Self for NAV distribution • A CTS frame with the RA field equal to its own MAC address (CTS-to-Self) and with a duration value that protects the pending transmission, plus possibly an ACK frame is transmitted at first • CTS-to-self is less robust against hidden nodes and collisions than RTS/CTS

  5. Overview of NAV distribution in MU-MIMO • NAV distributing frames contain a Duration field that defines the period of time that the medium is to be reserved to transmit the actual beamformed data frame and the returning response frames. By medium access rules NAV protection NAV distribution MU-MIMO data transmission AP Response frames STAs xIFS time xIFS time

  6. Possible approaches for NAV distribution using RTS/CTS in MU-MIMO • We are considering 3 different NAV distribution mechanisms for MU-MIMO transmissions • Multiple RTS/CTS exchanges • RTS and multiple CTS exchanges • CTS-to-self frame transmission Slide 6

  7. Multiple RTS/CTS exchanges for NAV distribution in MU-MIMO By medium access rules • Pros. • Using existing RTS and CTS frame formats • Supporting robust protection • Cons. • Having overhead problem for NAV distribution by using multiple RTS/CTS exchanges NAV protection AP RTS RTS RTS MU-MIMO data transmission SIFS Response frames SIFS time SIFS STA1 CTS STA2 CTS xIFS time xIFS time STA3 xIFS time CTS xIFS time NAV distribution Slide 7

  8. RTS and multiple CTS exchanges for NAV distribution in MU-MIMO By medium access rules • Pros. • Using existing CTS frame format • Supporting robust protection as same as the previous solution • Having less overhead problem for NAV distribution than the previous solution • Cons. • Using RTS frame with multiple destination information • Requiring accurate timing information to transmit each CTS frame without any transmitting address NAV protection AP RTS MU-MIMO data transmission Response frames xIFS time STA1 CTS xIFS time STA2 CTS xIFS time xIFS time STA3 CTS xIFS time NAV distributing NAV distribution Slide 8

  9. CTS-to-self frame transmission for NAV distribution in MU-MIMO By medium access rules • Pros. • Significantly reduces overhead compared with the previous solutions • Cons. • Supporting less robust against hidden nodes and collisions than the previous solutions NAV protection AP CTS MU-MIMO data transmission Response frames STA1 STA2 xIFS time STA3 xIFS time NAV distribution Slide 9

  10. Considerations on sounding exchange with NAV distribution mechanisms • Example of sounding exchange with RTS/CTS • Pros. • Reduces the overhead for sounding exchange • Cons. • CTS carried in a staggered sounding PPDU is may not be broadly received • does not provide robust protection • Separating the sounding exchange from the NAV distribution seems to be a better approach By medium access rules TRQ AP RTS Beamformed data transmission SIFS time SIFS time STA CTS Response frame Sounding PPDU SIFS time Slide 10

  11. Conclusion • Protection mechanisms for MU-MIMO transmission were considered • Possible approaches for NAV distribution using RTS/CTS in MU-MIMO • Multiple RTS/CTS exchanges • RTS and multiple CTS exchanges • CTS-to-self frame transmission • There are cons and pros for the above approaches • Need additional considerations for better solutions for NAV distribution • Need to separate the sounding exchange from NAV distribution • NAV distribution mechanisms carried in non-sounding PPDUs to protect the MU-MIMO data transmission and response frames seems to be a better approach • It is necessary to start discussing possible MU-MIMO protection mechanisms in TGac Slide 11

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