1. OBSS Mitigation Date: 2013-05-11 Authors: May 2013 Month Year
doc.: IEEE yy/XXXXr0
May 2013
OBSS Mitigation
Date:
Authors:
Name
Affiliations
Address
Phone
Shoukang Zheng
I2R
1 Fusionopolis Way, Singapore
Zander Lei
Li Chia Choo
Haiguang Wang
Yuan Zhou
Yeow Wai Leong
Huai-Rong Shao
Samsung
Chiu Ngo
ChaoChun Wang
MediaTek
San Jose, CA, USA
James Wang
Jianhan Liu
James Yee
Hsinchu, Taiwan
Thomas Pare
Kiran Uln
Eric Wong
Broadcom
Sunnyvale, CA, USA
Matthew Fischer
Minyoung Park
Intel
Hillsboro, OR, USA
Tom Tetzlaff
Emily Qi
Chao-Chun Wang, MediaTek
Shoukang ZHENG et. al, I2R, Singapore

2. Authors: March 2013 Name Affiliations Address Phone Email
Hongyuan Zhang
Marvell
Santa Clara, CA, USA
Su Khiong Yong
Sudhir Srinivasa
George Calcev
Huawei
Rolling Meadows, IL, USA
Osama Aboul Magd
Ottawa, Canada
Young Hoon Kwon
San Diego, CA, USA
Betty Zhao
Beijing, China
David Xun Yangxun
Shenzhen, China
Bin Zhen
Yongho Seok
LG Electronics
LG R&D Complex, Anyang, Korea
Jeongki Kim
Anyang, Korea
Jinsoo Choi
Hangyu Cho
Sun, Bo        
ZTE
Xi’an, China
Lv, Kaiying        
Simone Merlin
Qualcomm
Santosh Abraham
Menzo Wentink
Breukelen, Netherlands
Alfred Asterjadhi
Amin Jafarian
Hemanth Sampath
VK jones
Bin Tian
George Cherian
Chao-Chun Wang, MediaTek

3. Authors: March 2013 Name Affiliations Address Phone Email
Sayantan Choudhury
Nokia
Berkeley, CA, USA
Klaus Doppler
Chittabrata Ghosh
Esa Tuomaala
Ken Mori
Panasonic
Osaka, Japan
Rojan Chitrakar
Tai Seng Ave, Singapore
Minho Cheong
ETRI
138 Gajeong-no, Yuseong-gu, Daejeon, Korea
Hyoung Jin Kwon
Daejeon, Korea
Jae Seung Lee
Jae Woo Park
Sok-kyu Lee
Anna Pantelidou
Renesas Mobile
Oulu, Finland
Juho Pirskanen
Timo Koskela
Liwen Chu
STMicroelectronics
Santa Clara, CA, USA
George Vlantis
Chao-Chun Wang, MediaTek

4. May 2013
11ah OBSS issue
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
APL
STAL
APS
STAS
APS
STAS
STAO
Shoukang Zheng, I2R

5. 11ah OBSS issue - Continue
May 2013
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
May 2013
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. May 2013
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. May 2013
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
May 2013
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 STAS receiver 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
May 2013
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. May 2013
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