1. System Capacity Evaluation in OBSS Environment at 5 GHz band
Month Year
doc.: IEEE yy/xxxxr0
November 2010
System Capacity Evaluation in OBSS Environment at 5 GHz band
Date:
Authors:
T. Murakami et al.,(NTT)
John Doe, Some Company

2. Month Year
doc.: IEEE yy/xxxxr0
November 2010
Background
TGac agreed that inter-cell interference (ICI) in overlapping BSSs (OBSSs) environment is regarded as one of the main topics in coexistence ad-hoc group scope [1], [2].
The number of OBSSs will increase in the future.
TGac has already agreed to support 80 / 160MHz modes, which results in decrease the number of available channels [3], [4].
The number of APs and STAs supporting 11ac function will increase.
The objective of our research is to discover potential of each bandwidth modes in terms of system capacity on PHY layer against BSS density.
T. Murakami et al.,(NTT)
John Doe, Some Company

3. OBSS simulation model (1/2)
Month Year
doc.: IEEE yy/xxxxr0
November 2010
OBSS simulation model (1/2)
We evaluate system capacity per square meter against BSS density to consider influence of ICI.
Channelization for Europe and Japan operation in 11ac
Communication area
Bandwidth mode
[MHz] 20 40 80
160
Number of channels 19 9 4 2
Transmit power
per subcarrier*[mW] p
p/2
p/4
p/8
*Total transmit power is constant
BSS
Communication area
This area is defined by carrier sense level of each bandwidth modes. AP
Downlink
STA
T. Murakami et al.,(NTT)
John Doe, Some Company

4. OBSS simulation model (2/2)
Month Year
doc.: IEEE yy/xxxxr0
November 2010
OBSS simulation model (2/2)
BSS density D is defined by number of BSSs per square meter
few
many
Number of BSSs per square meter
Low
High
BSS density D
T. Murakami et al.,(NTT)
John Doe, Some Company

5. Simulation process Locate each BSS randomly.
Month Year
doc.: IEEE yy/xxxxr0
November 2010
Simulation process
Locate each BSS randomly.
The number of BSS corresponds to BSS density D.
Assign channel number to each BSS at random.
All BSSs use common bandwidth mode.
Each BSS tries to communicate:
If overlapping BSSs exist, only one AP can communicate to its STA. The other APs defer to communicate.
Non-overlapping BSSs can communicate at the same time.
Calculate capacity of the center BSS.
T. Murakami et al.,(NTT)
John Doe, Some Company

6. Simulation conditions
Month Year
doc.: IEEE yy/xxxxr0
November 2010
Simulation conditions
Number of Tx antennas Nt 4
Number of Rx antennas Nr 2
Bandwidth modes
20, 40, 80, 160 [MHz]
Transmit power per subcarrier
0, -3, -6, -9 [dBm]
BSS density D
1/1000-1/50 [number/m2]
MIMO channel model
i.i.d.
Path loss model
IEEE802.11n [5]
Distance b/w AP and desired STA
7.8 [m]
SNR b/w AP and desired STA for each bandwidth mode [dB]
25 (20 MHz), 22 (40 MHz)
19 (80 MHz), 16 (160 MHz)
Carrier sense level [dBm]
-82 (20 MHz), -79 (40 MHz)
-76 (80 MHz), -73 (160 MHz)
Slide 6
T. Murakami et al.,(NTT)
John Doe, Some Company

7. Month Year
doc.: IEEE yy/xxxxr0
November 2010
Calculation
Calculation formula of system capacity per square meter C is as follows:
B: bandwidth [MHz]
D: BSS density [number/m2]
N: number of iterations
Nsub: number of sub-carriers
Nfft: number of FFT points
K: number of active BSSs except center BSS
When a BSS transmits data at n-th iteration, its instantaneous capacity is:
Element of ICI
Otherwise:
T. Murakami et al.,(NTT)
John Doe, Some Company

8. System capacity vs. BSS density
Month Year
doc.: IEEE yy/xxxxr0
November 2010
System capacity vs. BSS density
Large house
Family apartment
Small apartment
As BSS density becomes higher, effectiveness of allocating wider bandwidth mode becomes lower.
This is because ICI from OBSSs increases.
In average Japanese apartment environment [6], 40 MHz mode is the best choice (D = 1/48m2.)
At low BSS density, system capacity of 160MHz is the best.
However, 160 MHz capacity is only 1.3 times that of 80 MHz although twice the bandwidth is used, because transmit power per sub-carrier becomes lower as bandwidth expands.
Low
density
High
density
 1/200m2
 1/100m2
 1/50m2
T. Murakami et al.,(NTT)
John Doe, Some Company

9. Month Year
doc.: IEEE yy/xxxxr0
November 2010
Summary
We evaluated system capacity per square meter on PHY layer against BSS density, assuming the current bandwidth modes (20, 40, 80, and 160 MHz).
We found that capacity for wider bandwidth mode at high BSS density becomes lower because ICI from OBSSs increases.
Also, we found that the wider bandwidth mode is allocated, the higher system capacity is achieved at low BSS density.
These results suggests that TGac should carefully specify the use wide bandwidth mode especially when BSS density is high.
T. Murakami et al.,(NTT)
John Doe, Some Company

10. Month Year
doc.: IEEE yy/xxxxr0
November 2010
References
[1] Rolf de Vegt et al., “Proposed Scope for Tgac Ad Hoc Groups,” Doc.: IEEE /1175r1.
[2] T. Takatori et al., “OBSS issue in ac,” Doc.: IEEE /0536r0.
[3] L. Cariou et al., “Evaluation of the saturation of the 5GHz band,” Doc.: IEEE /0846r2.
[4] R. Stacey et al., “Specification Framework for TGac,” Doc.: IEEE /0992r15.
[5] G. Smith, “TGaa OBSS background,” Doc.: IEEE /0762r0.
[6] B. A. H. S. Abeysekera et al., “Performance evaluation of MU-RTS under OBSS environment,” Doc.: IEEE /????r0.
Slide 10
T. Murakami et al.,(NTT)
John Doe, Some Company