1. daisuke.takeda@toshiba.co.jp noritaka.deguchi@toshiba.co.jp
January 2004
The sensitivity of performance to antenna element spacing when using the n Channel Model
Corporate Research & Development Center
Toshiba Corporation
Daisuke Takeda (Toshiba Corporation)

2. January 2004
The Concern
Antenna spacing used for simulations is not currently specified in the Comparison Criteria document.
Daisuke Takeda (Toshiba Corporation)

3. Objective 802.11n channel model
January 2004
Objective
802.11n channel model
Uniform linear array is mentioned in doc-940r1.
D=2pd / l ( d: Antenna spacing, l: Wavelength )
In doc-940r1, angular spread is defined for each channel model.
The minimum angular spread is less than 15 degree (Model B, 1st-cluster).
The maximum angular spread is more than 50 degree (Model F, 2nd-cluster).
Matlab channel model assumes 0.5l as typical parameter but it is not mandatory in Comparison Criteria.
(1)
Daisuke Takeda (Toshiba Corporation)

4. Objective (cont’d) Small angular spread Large angular spread
January 2004
Objective (cont’d) d d
Small angular spread
Antenna spacing is critical issue. (especially when antenna spacing d is small)
Large angular spread
Antenna spacing is not so critical.
Spatial Correlation
Spatial correlation is governed by Bessel Function.
Angular spread affects spatial correlation.
(may not be pure Bessel Function) r
J0(2p d /l) d
How much does antenna spacing affect PER performance?
Daisuke Takeda (Toshiba Corporation)

5. Simulation Parameters
January 2004
Simulation Parameters
Table 1 Simulation Parameters
Data Rate (per antenna)
6Mbps, 54Mbps
Number of Antenna
2x2, 3x3, 4x4
Antenna Shape
Linear Array
Antenna Spacing
(0.3, 0.5, 1, 1.5, 5) x l
Algorithm
MMSE-BLAST (OSIC)
Channel Model
802.11n (B,C,D,E)
Channel Estimation
Ideal
Synchronization
Daisuke Takeda (Toshiba Corporation)

6. Fig.1 Channel Model B (LOS)
January 2004
Fig.1 Channel Model B (LOS)
Daisuke Takeda (Toshiba Corporation)

7. Fig.2 Channel Model D (LOS)
January 2004
Fig.2 Channel Model D (LOS)
Daisuke Takeda (Toshiba Corporation)

8. Performance Improvement from 0.5l in Model B [dB]
January 2004
Table 2
Performance Improvement from 0.5l in Model B [dB]
at a PER of 10-2
0dB – 2dB
2dB – 4dB
> 4dB
Table 3
Performance Improvement from 0.5l in Model C [dB]
at a PER of 10-2
Daisuke Takeda (Toshiba Corporation)

9. Performance Improvement from 0.5l in Model D [dB]
January 2004
Table 4
Performance Improvement from 0.5l in Model D [dB]
at a PER of 10-2
0dB – 2dB
2dB – 4dB
> 4dB
Table 5
Performance Improvement from 0.5l in Model E [dB]
at a PER of 10-2
Not yet simulated.
Not yet simulated.
Daisuke Takeda (Toshiba Corporation)

10. From Simulation Results
January 2004
From Simulation Results
The performance difference is significant for Model B.
Due to narrow angular spread.
The performance difference for 0.5l and 1.0l spacing is 6dB at a PER of 10-2.
( 54Mbps, 3x3 case ).
Performance differences increase with the number of antennas.
The difference increases with data rate.
In 54Mbps, throughput performance will be seriously affected.
Daisuke Takeda (Toshiba Corporation)

11. January 2004
Conclusions
Performance varies appreciably with antenna spacing (by up to 6dB!)
It depends on channel model, data rate and number of antennas.
The comparison criteria must specify antenna spacing.
A fair comparison of proposals can only occur if the same antenna geometry and spacing are employed by everyone.
Hence, these parameters should be specified in the Comparison Criteria document for both the transmitter and receiver.
Daisuke Takeda (Toshiba Corporation)

12. January 2004
End
Daisuke Takeda (Toshiba Corporation)

13. Possible Solution? Antenna spacing should be specified as follows?
January 2004
Possible Solution?
Antenna spacing should be specified as follows?
Antenna Aperture : (m-1) x d
m : The number of antennas
d : Antenna spacing is 0.5l
(precise value to be decided).
Daisuke Takeda (Toshiba Corporation)

14. Fig.3 Channel Model C (LOS)
January 2004
Fig.3 Channel Model C (LOS)
Daisuke Takeda (Toshiba Corporation)

15. Fig.4 Channel Model E (LOS)
January 2004
Fig.4 Channel Model E (LOS)
Daisuke Takeda (Toshiba Corporation)

16. Spatial Correlation for Model B, Tap #3
January 2004
Spatial Correlation for Model B, Tap #3
Daisuke Takeda (Toshiba Corporation)