1. Benefits of Compressed Explicit feedback to resolve CID 2969
May 2007
doc.: IEEE /0xxxr0
May 2007
Benefits of Compressed Explicit feedback to resolve CID 2969
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Joonsuk Kim, Broadcom
Joonsuk Kim, Broadcom

2. CID 2969 in LB97 comments CID 2969 says
May 2007
CID 2969 in LB97 comments
CID 2969 says
“Since the complexity of processing the Compressed beamforming matrix is higher and the advantage in throughput is marginal (if any) when compared to non-Compressed beamforming, the Compressed beamforming matrix text should be deleted.”
This presentation shows the comment is wrong.
This includes a simple complexity analysis and overhead comparison for throughputs.
Joonsuk Kim, Broadcom

3. May 2007
Complexity
For example of 2x2, decomposition at Beamformee requires only 3 complex multiplies.
At Beamformer, finding V with angles needs only 2 complex multiplies.
Even with the worst case of 4x4, it may need only less than 40 complex multiplies, depending on how to implement it.
Compared with signal processing to find the SVD beamforming matrix V for example, this process is negligible in terms of complexity.
Joonsuk Kim, Broadcom

4. Overhead: Sample Simulations for 2x2 ch. B NLOS
May 2007
Overhead: Sample Simulations for 2x2 ch. B NLOS
Joonsuk Kim, Broadcom

5. Summary for channel E 2x2 3x3 4x2 4x4 Cartesian 280/570 504/1026
May 2007
Summary for channel E
The length of feedback data [Bytes] (BandWidth = 20MHz/40MHz)
2x2
3x3
4x2
4x4
Cartesian
280/570
504/1026
448/912
896/1824
Givens
56/114
168/342
210/428
336/684 (252/513)
Grouping 2
28/56
84/168
105/210
168/336 (126/252)
Grouping 4
14/28
42/84
53/105
84/168 (63/126)
For Givens/Grouping, 8,24,30,48(or 36) bits/tone are applied for 2x2,3x3,4x2,4x4 system, respectively, for the worst case of Channel E. For Channel D, Blue turns to Black, and Red turns to Blue.
Colors:
Black: PER performance penalty of 0dB~0.5dB compared to the full resolution BF
Blue: PER performance penalty of 0.5dB~1dB compared to the full resolution BF
Red: PER performance penalty of 1dB~1.5dB compared to the full resolution BF
Joonsuk Kim, Broadcom

6. May 2007
Conclusions
There are many benefits of compressed explicit feedback in overhead reduction with minimal aid of the beamformee to determine the angles for feedback.
Compared to the complexity of finding SVD beamforming matrix V, additional process to determine angles are negligible.
95% of overhead reduction compared to Non-compressed explicit feedback is NOT “marginal”.
Since the reasons for the comment in CID 2969 are wrong, it is proposed to reject CID 2969.
Propose: Reject on the ground that BEAM adhoc group agreed there are many benefits of compressed explicit feedback in terms of complexity and overhead reduction compared to Non-compressed explicit feedback as shown in 07/0666r0.
Joonsuk Kim, Broadcom