Overlapping BSS Co-Existence November 2010 doc.: IEEE 802.11-10/1303r0 November 2010 Overlapping BSS Co-Existence Date: 2010-11-11 Authors: Jarkko Kneckt (Nokia) Jarkko Kneckt (Nokia)

November 2010 doc.: IEEE 802.11-10/1303r0 November 2010 Abstract The presentation describes enhancements for overlapping BSS co-existence The presentation provides guidance how to detect the OBSS and the overlapping channels The presentation describes rules and related methods for transmissions in overlapping channels Jarkko Kneckt (Nokia) Jarkko Kneckt (Nokia)

November 2010 Problem Statement The 802.11ac will increase number of cases in which the primary and the non-primary channels overlap Currently 802.11ac has inadequate rules and means to protect a primary channel over a non-primary channel Jarkko Kneckt (Nokia)

Targets of the Channels Protection November 2010 Targets of the Channels Protection The legacy 802.11a/n with 20 MHz have NAV protection present in all TXOPs Protection level of 802.11ac should be at similar level or better even with capacity enhancements The protection mechanism should be scalable The protection overhead should be minimized The maximum protection level is not needed in every scenario Scalability is w.r.t, the number of the operating channels and the number of OBSSs Jarkko Kneckt (Nokia)

Background Information November 2010 Detecting OBSS Background Information Each device calculates backoff and receives transmissions in its primary channel The AP receives a 802.11ac PLCP header with unallocated Group ID or Nsts values The STA receives a 802.11ac PLCP header but cannot decode a frame The STA receives a frame with a foreign BSSID Through scanning: Scanning enables STA to detect BSSs that overlap only at non-primary channel(s) AP may scan or command associated STA(s) to scan OBSS Jarkko Kneckt (Nokia)

Background Information November 2010 OBSSs Examples Background Information Single 802.11ac BSS in 80 MHz mode has the following possibilities to overlap: The primary channels of the BSSs are at the same channel The NAV information is shared between BSSs The other BSS transmits at the non-primary channels Legacy 802.11a/n BSS may transmit only in non-primary channels Non-congested 802.11ac BSS may transmit only in subset, i.e. primary and secondary , channels The other 802.11ac BSS transmitting at the same operating channels The other 802.11ac BSS operating in 160 MHz mode 160 MHz BSS may have its primary channel at separate 80 MHz channel Jarkko Kneckt (Nokia)

Primary Channel Selection Rules November 2010 Background Information Primary Channel Selection Rules The local BSS or OBSS may change its primary channel The operating channels of the BSS are derived from the primary channel AP may change the BSS primary channel to the same primary channel as OBSS and thus NAVs are visible to each other AP should select the BSS primary channel to avoid overlapping operating channels Jarkko Kneckt (Nokia)

November 2010 Problem Statement The 802.11ac will increase the number of cases in which the primary and the non-primary channels overlap Currently 802.11ac has inadequate rules and means to protect a primary channel over a non-primary channel The enhanced RTS CTS scheme only considers CCA of the transmitter and recipient: NAV protection of other BSS transmissions at non-primary channels cannot be received Jarkko Kneckt (Nokia)

Challenge: Protecting Primary Channel over a Non-primary Channel November 2010 Challenge: Protecting Primary Channel over a Non-primary Channel The operating channels of the BSSs may partially overlap The primary channel of the 160 MHz mode BSS may be outside the 80 MHz operating channel of other BSS The NAV information is received if transmitted in primary channel The BSS should have means to protect its transmissions at primary channel The 160 MHz mode BSSs should have means to share non-primary 80 MHz channels Jarkko Kneckt (Nokia)

Improved Co-existence: NAV to Protect Primary Channel November 2010 Improved Co-existence: NAV to Protect Primary Channel TXOP holder commands a selected STA to send a frame(TBD) to other BSS’s primary channel The primary channel of other BSS doesn’t overlap with channels reserved by TXOP holder The frame sets NAV for the channels reserved by TXOP holder Justification: Enables BSS to protect its primary channel over secondary channels Avoids hidden terminal problems Improves the efficiency of the non-primary channels sharing Jarkko Kneckt (Nokia)

Example Protecting Primary Channel November 2010 Example Protecting Primary Channel The BSS2 operates in 80MHz mode and BSS1 operates in 160 MHz mode A TXOP holder in BSS2 commands a STA to send a frame to primary channel of BSS1 to protect the ongoing transmission and indicate presence of its primary channel The recipients shall not use the channels for the duration as indicated in the frame Jarkko Kneckt (Nokia)

Example Sharing Non-Primary Channels November 2010 Example Sharing Non-Primary Channels Two BSSs are operating in a non-contiguous 160 MHz transmission mode The TXOP holder commands with a frame the reserving STA to send a frame to primary channel of BSS2 The recipients shall not use the channels for the duration as indicated in the frame Jarkko Kneckt (Nokia)

Challenge: Increasing TXOP Bandwidth November 2010 Challenge: Increasing TXOP Bandwidth The TXOP holder may test availability of the non-primary channels for a PIFS duration If energy level of the channels is below the CCA threshold, the TXOP holder may transmit at the channels In theory this is similar to allowing a STA to issue active scanning after a PIFS The operation is prone to hidden terminal problems the TXOP holder has no knowledge of the virtual carrier sensing at the non-primary channels Jarkko Kneckt (Nokia)

Improved Co-Existence: Virtual Carrier Sensing by Reserving STA November 2010 Improved Co-Existence: Virtual Carrier Sensing by Reserving STA Reserving STA reserves more non-primary channels The TXOP holder specifies the reserving STA, the channels to be reserved and the time of reporting The reserving STA follows the orders of the TXOP holder The reserving STA temporarily contends at the channels it is reserving The reserving STA synchronizes to the channel to be reserved The reserving STA transmits a frame to reserve the channel At the reporting time, the reserving STA signals success to TXOP holder Jarkko Kneckt (Nokia)

Example Increasing TXOP Bandwidth November 2010 Example Increasing TXOP Bandwidth The TXOP holder commands with a frame the reserving STA to reserve the secondary channel The reserving STA is capable to reserve the secondary channel and indicates the success at the time reporting time, specified by the TXOP holder Similar operation is repeated for tertiary and quaternary channels Please note: The timing of the OK transmission may be freely decided by AP, i.e. no need to overlap with ACK transmission time Any reservation mechanism may be used, i.e. not limited by proposal Jarkko Kneckt (Nokia)

Summary The problems are: November 2010 Summary The problems are: Blind entry to the channel Primary channel transmissions colliding with blind secondary channel transmissions This presentation provides the solutions to the problems: Synchronization with the channel to be reserved Protecting and prioritizing primary channel transmissions over secondary channel transmissions Jarkko Kneckt (Nokia)

November 2010 Strawpoll Do you agree with the targets of channels protection as listed below? The Protection level of 802.11ac should be at similar level or better than the legacy 802.11a/b/g/n even with capacity enhancements The protection mechanism should be scalable The protection overhead should be minimized The maximum protection level is not needed in every scenario Scalability is w.r.t, the number of the operating channels and the number of OBSSs? Yes No Jarkko Kneckt (Nokia)

November 2010 Strawpoll Are you in favor of having NAV protection available as described in slides 10 -12 in this presentation? Yes No Jarkko Kneckt (Nokia)

November 2010 Strawpoll Are you in favor of using reserving STA to enable better co-existence? Yes No Jarkko Kneckt (Nokia)