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

2. November 2010
doc.: IEEE /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)

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

4. Targets of the Channels Protection
November 2010
Targets of the Channels Protection
The legacy a/n with 20 MHz have NAV protection present in all TXOPs
Protection level of ac 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)

5. Background Information
November 2010
Detecting OBSS
Background Information
Each device calculates backoff and receives transmissions in its primary channel
The AP receives a ac PLCP header with unallocated Group ID or Nsts values
The STA receives a ac 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)

6. Background Information
November 2010
OBSSs Examples
Background Information
Single ac 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 a/n BSS may transmit only in non-primary channels
Non-congested ac BSS may transmit only in subset, i.e. primary and secondary , channels
The other ac BSS transmitting at the same operating channels
The other ac BSS operating in 160 MHz mode
160 MHz BSS may have its primary channel at separate 80 MHz channel
Jarkko Kneckt (Nokia)

7. 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)

8. November 2010
Problem Statement
The ac will increase the number of cases in which the primary and the non-primary channels overlap
Currently ac 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)

9. 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)

10. 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)

11. 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)

12. 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)

13. 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)

14. 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)

15. 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)

16. 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)

17. November 2010
Strawpoll
Do you agree with the targets of channels protection as listed below?
The Protection level of ac should be at similar level or better than the legacy a/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)

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

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