1. OBSS issue and simulation scenarios in TGac
Month Year
doc.: IEEE yy/xxxxr0
November 2009
OBSS issue and simulation scenarios in TGac
Authors:
Yasushi Takatori (NTT)
John Doe, Some Company

2. November 2009
Outline
Background
Measured propagation loss in a typical Japanese apartment
Difference between OBSS issue in TGac and that in TGaa
OBSS simulation scenarios in TGac
Video Streaming with 11ac devices
Yasushi Takatori (NTT)

3. November 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 video streaming[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 video streaming but also for other traffic.
Yasushi Takatori (NTT)

4. Measured propagation loss in a typical Japanese apartment
November 2009
Measured propagation loss in a typical Japanese apartment
Yasushi Takatori (NTT)

5. Measurement place 6 1 2 3 4 5 7 3.0 m 7.3 m November 2009
Yasushi Takatori (NTT)

6. Layout of each room in the measurement place
November 2009
7.3 m S1 1 S2 S5
3.0 m S3 S4 2
AP　 Number of antennas = 8, Linear array (Spacing 0.5λ)
STA　 Number of antennas = 4, Linear array (Spacing 0.5λ)
S *
Yasushi Takatori (NTT)

7. Measurement equipment
November 2009
4x8 MIMO channel measurement was carried out for SDMA evaluation.
Long preamble signal is continuously transmitted.
Interference between two APs or AP/STA is assumed in this measurement.
Rx (AP) : 8 element
h = 2.12 m
Tx (STA) : 4 element
h = 2.12/0.9, 0.75 m
AGC
Down-conv.
LNA
HPA
Up-conv.
D/A
A/D
AGC
Down-conv.
LNA
Up-conv.
HPA
D/A
A/D
AGC
Up-conv.
Down-conv.
LNA
D/A
HPA
A/D
HPA
Up-conv.
D/A
AGC
Down-conv.
LNA
A/D
Channel estimator
TCP-IP
Yasushi Takatori (NTT)

8. Image of interference from OBSS
November 2009
Image of interference from OBSS
(other person’s room)
(my room) AP AP
(OBSS)
(desired)
Measured path
STA
(OBSS)
(desired)
STA
Yasushi Takatori (NTT)

9. Measurement parameters
November 2009
Measurement parameters
Frequency GHz
Bandwidth MHz (20MHz x 2)
Signal OFDM signal
Number of FFT
Number of subcarrier (Legacy .11a mode)
Antenna height m (Rx side)
0.75m (Tx side)
Yasushi Takatori (NTT)

10. Results on Interference power
November 2009
Results on Interference power
~ Horizontal neighborhood rooms~ AP
(Case 1)
(Case 1)
[dBm]
-74.46
-68.28
-63.52
-56.89
-50.18 3m
Averaged.
-76.54
-69.18
-64.63
-56.23
-45.79
height = 2.12 m
(Case 2) AP
(Case 2)
[dBm]
-78.61
-69.98
-65.73
-55.57
-41.39 3m
height = 0.9 m
Yasushi Takatori (NTT)

11. Measurement result agrees with the path-loss model in TGn [2].
November 2009
-22
-32
-42
-52
-62
-72
-82
-92
TGn Model [3]
Measurement Result
Measurement result agrees with the path-loss model in TGn [2].
Relative Received Power [dB]
Indoor propagation loss formula (11n) *, F in MHz, d in feet
For d<16.5ft
Lp = – log F + 20 log d + Wall/Floor loss (Free Space formula)
For d>16.5ft
Lp = – log F + 20 log log (d/16.5) + Wall/Floor Loss
Yasushi Takatori (NTT)

12. Summary for measured propagation loss
November 2009
Summary for measured propagation loss
When considering the interference betweens rooms on
horizontal direction, interference seems to be almost the same
with the TGn model.[2] Hence, the model in TGn seems
to be reasonable in the evaluation of OBSS in the apartment.
As well as described in [2], this result shows the influence on
the interference by OBSSs is serious problem in Japanese apartment.
OBSS in TGac would be a serious problem because 80MHz bandwidth is likely to be used.
Slide 12
K.Nishimori, T. Murakami, R.Kudo, Y.Takatori, Y.Asai (NTT)
Yasushi Takatori (NTT)

13. Difference between OBSS issue in TGac and that in TGaa
November 2009
Difference between OBSS issue in TGac and that in TGaa
Yasushi Takatori (NTT)

14. November 2009
July xx, 2009
OBSS issue in TGaa [2][3]
OBSS issue in TGaa is focusing on video streaming.
Frequency channel assignment and time sharing mechanism have been developed to support video streaming 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 14
Yasushi Takatori (NTT)
Names

15. Frequency band allocation in Japan
OBSS Issue in TGac
November 2009
OBSS issue is important in TGac because frequency channel shortage is expected.
OBSS issue in TGac is not only for video streaming but also for other traffic.
Frequency channel assignment algorithm using TGaa approach may mitigate OBSS effect.
However, TGaa approach seems not to be directly applicable to 11ac 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)

16. November 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)

17. Possible Interference Management
November 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)

18. Basic flow to mitigate influence of OBSS
November 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)

19. Summary of possible approaches
November 2009
OBSS issue is important in TGac because frequency channel shortage is expected. It is not only for video streaming but also for other traffic.
TGaa has addressed OBSS issue to support video streaming in OBSS. Other general traffic is not taken into account.
Frequency channel assignment and time sharing mechanism have been developed in TGaa to support video streaming 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)

20. OBSS Simulation Scenario in TGac
November 2009
OBSS Simulation Scenario in TGac
There two scenarios, enterprise scenario [6] and home network scenario [7].
The following slides explain home network scenario with OBSS.
Yasushi Takatori (NTT)

21. Home Network Evaluation Scenario
November 2009
Home Network Evaluation Scenario
To simplify OBSS scenario, the following effects are focused on.
Overlapping with 11ac
Overlapping with 11n
Effect of hidden terminals in OBSS
Throughput degradation from isolated Home Entertainment scenario
Evaluation model
BSS A: In-Home entertainment application
BSS B: 11ac with 3 STAs
BSS C: 11n with 3 STAs
Room walls are inserted to evaluate effect of hidden terminals
Yasushi Takatori (NTT)

22. November 2009
AP and STA locations
Attenuation factors of room wall and outside wall are TBD.
11n
In-home entertainment application
11ac
Yasushi Takatori (NTT)

23. Channel Assignment BSS A,B BSS C Case 1 Frequency 80MHz BSS A,B BSS C
November 2009
Channel Assignment
BSS A is identical to the BSS in TGac scenario #3
BSS B is an 11ac BSS
BSS C is a upper 40MHz n BSS
Both 11ac have the same bandwidth (40MHz or 80MHz)
BSS A,B
BSS C
Case 1
Frequency
80MHz
BSS A,B
BSS C
Case 2
Frequency
80MHz
Yasushi Takatori (NTT)

24. Traffic flow at overlapping BSS B
November 2009
Traffic flow at overlapping BSS B
Flow number 1 and 12 in simulation scenario #3 are considered.
Flow No.
STAs
(Source/Sink)
Source Location
(meters)
Sink Location
Channel Model
Application
(Forward Traffice / Backward Traffic)
Application Load (Mbps)
(Forward / Backward)
Rate Distribution
MSDU Size (B)
Max. Delay (ms)
Max.
PLR 1
AP / STA1
(0,0)
(0,5) C
LC Video / VoD control channel
/ 0.06
Constant, UDP / Constant UDP
1500 / 64
10 / 100
 10^-7 / 10^-2 12
STA4 / STA10
 (-7,7)
 (10,10)
Local file transfer
Max. 1Gbps
TCP
300
Inf.
 N/A
Yasushi Takatori (NTT)

25. Traffic flow at overlapping BSS C
November 2009
Traffic flow at overlapping BSS C
Flow No.1 in BSS B is changed to Flow No.1 of n scenario #1.
Flow No.
STAs
(Source/Sink)
Source Location
(meters)
Sink Location
Channel Model
Application
(Forward Traffice / Backward Traffic)
Application Load (Mbps)
(Forward / Backward)
Rate Distribution
MSDU Size (B)
Max. Delay (ms)
Max.
PLR 1
AP / STA1
(0,0)
(0,5) C
HDTV(Video / Audio) / VoD control channel
19.2 / 0.06
Constant, UDP / Constant UDP
1500 / 64
200 / 100
 10^-7 / 10^-2 12
STA4 / STA10
 (-7,7)
 (10,10)
Local file transfer
Max. 1Gbps
TCP
300
Inf.
 N/A
Yasushi Takatori (NTT)

26. November 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.
[6] Brian Hart, Enterprise Simulation Scenario, IEEE /816r5, Sept. 22, 2009.
[7] Yasushi Takatori, et al., Home Network Simulation Scenario with OBSS, Doc. IEEE /1076r0.
Yasushi Takatori (NTT)

27. November 2009
Video Streaming in 11ac
There seems to be three possibilities to support video streaming services with 11ac devices.
(A) 11aa + 11ac: Simple combination
(B) 11aa+ + 11ac: Creation of new standard, 11aa+
(C) 11ac only: Basic functions of 11aa are supported by 11ac
Question:
Which one is suitable for video streaming services with 11ac devices?
(A) 11aa + 11ac:
(B) 11aa+ + 11ac:
(C) 11ac only:
Yasushi Takatori (NTT)