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 the 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/b/g/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. November 2010
Detecting OBSS
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. November 2010
OBSSs Examples
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
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. Reception of PLCP Headers
November 2010
Reception of PLCP Headers
A copy of PLCP header is present at each 20 MHz channel of the transmission
PLCP Header is received, if any of the transmitted 20 MHz channels is the primary channel of the recipient
PLCP headers contain length, modulation and coding information of the PPDU
The duration of the PPDU may be calculated
Jarkko Kneckt (Nokia)

9. Protecting TXOP Continuation with PLCP
November 2010
Protecting TXOP Continuation with PLCP
The PLCP headers provide simple protection for acknowledgment transmission and TXOP continuation
Nsts and Group ID fields of VHT-SIG A indicate is the transmission addressed to individual or group address
The channel access after individually addressed PPDU should start after acknowledgment transmission
The channel access after group addressed PPDU should start after PPDU transmission
Jarkko Kneckt (Nokia)

10. November 2010
PLCP to Protect TXOP
Jarkko Kneckt (Nokia)

11. Layers of Channel Protection and Estimation Mechanisms
November 2010
Layers of Channel Protection and Estimation Mechanisms
The legacy a/g transmits every PPDU at the same channel, resulting to double protection for the PPDUs
The NAV information is updated frequently
ACKs are typically transmitted in low rate, i.e. ACKs distribute NAV information to wide coverage
The CCA protection works, SIFS between PPDUs is shorter than channel access time
Jarkko Kneckt (Nokia)

12. Layers of Channel Protection and Estimation Mechanisms
November 2010
Layers of Channel Protection and Estimation Mechanisms
The NAV information in ac transmissions is available in SU transmissions at primary channel
NAV information in MU MIMO transmissions may not receivable any channel
TXOP has easily holes, i.e. ACKs are transmitted in single channel. This reduces the reliability of CCA detection
The ac needs virtual carrier sensing updates during the TXOP
The PLCP header sets protection for ACK transmission
The RTS CTS mechanism may generate heavy overhead for short transmissions
The information to provide protection for ACK transmission times is already available at VHT PLCP headers, no new fields are needed
Jarkko Kneckt (Nokia)

13. Single STA Limitations
November 2010
Single STA Limitations
Single STA is not capable to:
Use virtual carrier sensing when it reserves non-primary channels
Set NAV protection to its transmission when the primary channel of other BSS is not part of the transmission
These operations are possible by using reserving STA
The reserving STA follows orders of the TXOP holder
Jarkko Kneckt (Nokia)

14. Co-existence Challenge 1: Increasing TXOP Bandwidth
November 2010
Co-existence Challenge 1: 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
The operation is prone to hidden terminal problems
the TXOP holder has no knowledge of the ongoing transmissions at the non-primary channels it is reserving
Jarkko Kneckt (Nokia)

15. 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 changes its primary channel to a channel it is reserving
The reserving STA maintains NAV and PLCP protection for the channels it is reserving
The reserving STA transmits a frame to reserve the channels
At the reporting time, the reserving STA signals success to TXOP holder
Jarkko Kneckt (Nokia)

16. November 2010
Example
The TXOP holder commands with PMP 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
Jarkko Kneckt (Nokia)

17. Co-Existence Challenge 2: Partially Overlapping Channels
November 2010
Co-Existence Challenge 2: Partially Overlapping Channels
The operating channels of the BSSs may partially overlap
The primary channels of the 160 MHz mode BSS may be outside the 80 MHz operating channel of other BSS
The NAV or PLCP information are received if they are transmitted to primary channel
The BSS should have means to protect its transmissions at primary channel
Similarly the non-contiguous 160 MHz BSSs should have means to multiplex non-primary 80 MHz channels
Jarkko Kneckt (Nokia)

18. Improved Co-existence: NAV to Partially Overlapping Channels
November 2010
Improved Co-existence: NAV to Partially Overlapping Channels
TXOP holder commands selected STA(s) to send a frame to other BSS primary channel(s)
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
The CTSS frame enables BSSs to multiplex the same resources
The NAV information of the reserved channels avoid hidden terminal problems
Jarkko Kneckt (Nokia)

19. November 2010
Example
Two BSSs are operating in non-contiguous 160 MHz transmission mode
The TXOP holder commands with PMP frame the reserving STA to send TXOP holder channel reservation information to IEEE channels 60 – 63
The reserving STA transmits CTSS frame to set NAV for channels reserved by the TXOP holder
The BSS2 shall not use IEEE channels 100 – 115 during the period indicated in CTSS
Jarkko Kneckt (Nokia)

20. Thank You Questions, suggestions and comments are welcome.
November 2010
Thank You
Questions, suggestions and comments are welcome.
Jarkko Kneckt (Nokia)

21. November 2010
Strawpoll
Do you agree with the targets of channels protection as listed below?
The legacy a/b/g/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?
Yes No
Abstain
Jarkko Kneckt (Nokia)

22. November 2010
Pre-Motion
Do you support adding the following text into specification framework document, 11-09/992?
Clause 5.2 Backoff procedure:
When the Group ID and Nsts fields of the VHT-SIG A field of the PLCP header indicate that transmission is addressed to individual address, the channel shall be considered busy for duration of the PPDU, SIFS and ACKDuration(44ys).
Yes No
Abstain
Jarkko Kneckt (Nokia)

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

24. November 2010
Strawpoll
Are you in favor of having NAV protection available for partially overlapping channels?
Yes No
Abstain
Jarkko Kneckt (Nokia)