1. Consideration on Interference Management in OBSS
Month Year
doc.: IEEE yy/xxxxr0
July 2009
Consideration on Interference Management in OBSS
Authors:
Yasushi Takatori (NTT)
John Doe, Some Company

2. July 2009
Background
TGac agrees that it is important to see how 11ac devices behave in OBSS [1].
TGaa has addressed OBSS issue for video streaming. Frequency channel assignment and time sharing mechanism have been developed to support QoS in OBSS [2].
OBSS in TGac is caused by both possible frequency band enlargement and increase in the number of WLAN devices.
The behavior of 11ac devices in OBSS should be examined not only for QoS traffic but also for other traffic.
Yasushi Takatori (NTT)

3. July 2009
July xx, 2009
OBSS issue in TGaa [2][3]
OBSS issue in TGaa is focusing on QoS support.
Frequency channel assignment and time sharing mechanism have been developed to support QoS in OBSS.
Simple competition among general traffic is considered to be sufficient.
Information of QoS traffic load is advertised among multiple BSSs.
QAP-1
QAP-2
Qload
EDCA or HCCA
EDCA or HCCA
Frequency Channel K1
Frequency Channel K2
STA-11
STA-21
Slide 3
Yasushi Takatori (NTT)
Names

4. Frequency band allocation in Japan
OBSS Issue in TGac
July 2009
OBSS issue is important in TGac because frequency channel shortage is expected.
OBSS issue in TGac is not only for QoS traffic but also for other traffic.
Frequency channel assignment algorithm using TGaa approach may mitigate OBSS effect. However, TGaa approach cannot be directly applied because TGac should take into account other traffic also.
Frequency band allocation in Japan
20MHz mode
5150
5190
5230
5250
5270
5310
5350[MHz]
40MHz mode
(80MHz mode)
5470
5510
5550
5590
5630
5670
5710
5725[MHz]
Yasushi Takatori (NTT)

5. July 2009
Direction
Time resource is fairly shared by CSMA/CA with RTS/CTS mechanism [2]. SDMA scheme in 11ac should not degrade this level of fairness. Sharing scheduling information among multiple BSSs may improve the throughput [5].
Interference management has a potential to achieve further throughput improvement in OBSS. It has been also addressed in TGaa [2][3][4].
Yasushi Takatori (NTT)

6. Possible Interference Management
July 2009
Possible Interference Management
Frequency domain:
Access mechanism that enables frequency channel assignment would be devised to use 80MHz bandwidth for all traffic. (For 11aa case, see [2])
Falling back to narrowband mode, e.g. 20/40MHz mode, can be one of the practical solutions. (For 11aa case, see [3])
Spatial domain.:
Transmission power control (TPC) might be effective to decrease the number of OBSSs.
(TGh addressed TPC to avoid interference to other systems. Although it is effective in an apartment scenario, TPC might cause range limitation in other scenarios [4].)
Beamforming might be also useful because 11ac devices already have beamforming capability to enable MU-MIMO.
Yasushi Takatori (NTT)

7. Basic flow to mitigate influence of OBSS
July 2009
Basic flow to mitigate influence of OBSS
(1) OBSS detection
Carrier Sensing
Others
(2) Exchanging control messages
RTS/CTS mechanism
TRM/Sounding signals
(Advertisement of Qload)
(3) Resource allocation
NAV setting
(Frequency channel selection)
(TPC/Beamforming )
(4) Data transmission
(5) ACK
(1)
(3)
(1)
(3)
(2)
AP-1
AP-2
(2)
(2)
(2)
(2)
(4)
(4)
(5)
(5)
(2)
STA-11
STA-21
Yasushi Takatori (NTT)

8. Summary
July 2009
OBSS issue is important in TGac because frequency channel shortage is expected. It is not only for QoS traffic but also for other traffic.
TGaa has addressed OBSS issue to support QoS in OBSS. Other general traffic is not taken into account.
Frequency channel assignment and time sharing mechanism have been developed in TGaa to support QoS in OBSS.
The following interference management approaches are suggested.
Frequency domain approach:
Modification of TGaa mechanism is one of the possible approaches.
Frequency channel assignment / Falling back to narrow band modes
Spatial domain approach:
Interference management with TPC / Beamforming
Yasushi Takatori (NTT)

9. July 2009
References
[1] Yasushi Takatori, “Importance of Overlapped BSS issue in ac,” Doc. IEEE /0630r1.
[2] Graham Smith, “TGaa OBSS Background,” Doc. IEEE /0762/r0.
[3] Graham Smith, “20/40MHz Channel Selection,” Doc. IEEE /0740/r0.
[4] Graham Smith, et al., “Overlapping BSS Proposed Solution,” Doc. IEEE /0457/r3.
[5] Yuichi Morioka, “Two Levels of OBSS Control in 11ac ,” Doc.IEEE /0833/r0.
Yasushi Takatori (NTT)