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OBSS Mitigation

OBSS Mitigation. Authors:. Date: 2013-05-11. Authors:. Authors:. 11ah OBSS issue. AP L. STA L. AP S. STA S. AP S. STA S. STA O. A long range BSS may enclose and overlap spatially with several short range BSSs

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OBSS Mitigation

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  1. OBSS Mitigation Authors: Date: 2013-05-11 Chao-Chun Wang, MediaTek

  2. Authors: Chao-Chun Wang, MediaTek

  3. Authors: Chao-Chun Wang, MediaTek

  4. 11ah OBSS issue APL STAL APS STAS APS STAS STAO • A long range BSS may enclose and overlap spatially with several short range BSSs • An STAL associated with the long range APL that is not within the coverage of one or more short range BSSs. • An STAO associated with the long range APL that is also overlapped within the coverage of a short range BSS. • An STAS is associated with a short range APS that is also within the coverage of a long range BSS ShoukangZheng, I2R

  5. 11ah OBSS issue - Continue • A long range BSS has a coverage area radius that is multiples of that of a short range BSS. • A long range BSS has narrow 1 or 2 MHz channel bandwidth, while a short range BSS has wider bandwidth, such as 2, 4, 8 MHz • A STAS is capable of receiving 1 and 2 MHz frames and a STAL is capable of receiving 1 MHz frames only • Without loss of generality, we assume • the long range BSS occupies a 2 MHz channel and each short range BSS occupy 8 MHz band, consisting of four 2 MHz band. • In the short range BSS, the protection period is set up by using duplicate RTS/CTS • The RTS/CTS has range covering the short range BSS only Chao-Chun Wang, MediaTek

  6. Setting TXOP for STAs using duplicate RTS/CTS • A transmitting STAs sends duplicate RTS frames to all 2 MHz sub-channels, primary and secondary. • In response, duplicate CTS frames are sent to all usable 2MHz sub-channels • The receiver decides the best usable channel bandwidth based on the channel measurements prior to the receiving of duplicate RTSs • The transmitter exchanges frames with the receiver by using the bandwidth indicated in the duplicate CTS. • Duplicate ACKs are returned on primary and all usable secondary channels Chao-Chun Wang, MediaTek

  7. Problem Statement - 1 • Non-overlapping (in frequency domain) long range BSSs enclosing multiple non-overlapping (in spatial domain) short range BSSs • A short range BSS and a long range BSS that share the primary channel co-exist according to the current channel access rule. • The APss and STAss will hear the traffic of a long range BSS sharing the primary channel and set up a NAV for collision avoidance scheme accordingly. • The APLs and STALs on the secondary channels may not hear the traffic or TXOP set up in a short range BSS sharing the primary channel and may interfere with the traffic in the short range BSS. Chao-Chun Wang, MediaTek

  8. Problem Statement - 2 • Long range BSSs on the secondary channels of a short range BSS may not hear TXOP set up of the short range BSS and will access channel according to CCA rules • As a result, the traffic in the long range BSSs occupying secondary channels may collide with the traffic in short range BSSs and causes data loss. • In response, the STAS and STAL may re-transmit and continue to collide. • With information about the condition of secondary channels, the re-transmission process will converge faster • STAL and STAS need to co-exist fairly Chao-Chun Wang, MediaTek

  9. Secondary Channel Interference • Long range STALs exchange RTS/CTS in a 1 or 2 MHz channel to set up a TXOP in a secondary channel. • The TXOP of the long range BSS overlaps with the TXOP set up by the short range BSSs • Long range STALs and short range STASs exchange frames around the same time. • The collision may not affect the STALs in the secondary channel but will corrupt data destined for the STASs . • The STASreceiver can estimates the interference level of the secondary channels based on Rx statistics • It is a vendor specific capability. It is up to a vendor to decide how or whether to support it Chao-Chun Wang, MediaTek

  10. Usable Channel Indication by using duplicate ACKs • An STAS transmitter starts transmitting using the primary channel and all secondary channels available. • A STAS returns duplicate ACKs with reduced bandwidth to the transmitter • The transmitter can avoid the secondary channels with the high level of interference in the succeeding transmission • The STAss will not interfere STAls sharing a second channel • Duplicate ACKs to reduce the channel bandwidth • The receiver returns duplicate short ACKs on the primary and usable secondary channels only. • Only return duplicate short ACKs on contiguous channels • Subsequently, the STAS transmitter data only on the secondary channel indicated as usable by duplicate ACKS. Chao-Chun Wang, MediaTek

  11. Straw Poll Do you support the inclusion of the usable channel indication mechanism follows and includes transmitter and receiver capability information • When the data is received correctly by a receiver: • The receiver returns full bandwidth >= 2MHz short ACK on the primary and usable secondary channels. • Only return full bandwidth >= 2MHz short ACKs  on contiguous channels Chao-Chun Wang, MediaTek

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