1. Average SNR Definition CID 3241
Month Year
doc.: IEEE /2451r1
September 2007
Average SNR Definition CID 3241
Date:
Authors:
Vinko Erceg, Broadcom Corporation
Vinko Erceg, Broadcom Corporation

2. Month Year
doc.: IEEE /2451r1
September 2007
CID 3241 Text
CID 3241
3241
50.00
"..where SNR_average is the dB value of linear power averaged over the tones represented. This encoding covers the SNR range from -10 to in 0.25 dB steps." It may be better to average dB values.
Change to: Sum of the dB values divided by the number of values summed.
Vinko Erceg, Broadcom Corporation
Vinko Erceg, Broadcom Corporation

3. September 2007
Discussion
Together with CSI and compressed/uncompressed matrix feedback, average SNR values are provided.
In the current n Draft (2.07), the average SNR is defined as “dB value of the linear average” for CSI and compressed/uncompressed feedback cases.
For the CSI case, the average SNR represents:
SNR in Rx channel 1:Nr
8 bits
Signal to Noise Ratio in 1:Nr Rx chains of the STA sending the report.
Vinko Erceg, Broadcom Corporation

4. Month Year
doc.: IEEE /2451r1
September 2007
Discussion: Cont’
For the compressed/uncompressed case, the average SNR has quite different meaning:
SNR for stream 1:Nc
8 bits
Average Signal to Noise Ratio in the STA sending the report for stream 1:Nc.
Vinko Erceg, Broadcom Corporation
Vinko Erceg, Broadcom Corporation

5. September 2007
Discussion: Cont’
For the CSI feedback average SNR represents Rx chain SNR but for compressed/uncompressed feedback it represents SNR per spatial stream.
These are 2 different SNRs that are often regarded as “pre-processing SNR” in the case of the CSI feedback and “post-processing SNR” in the case of the compressed/uncompressed feedback.
They require different SNR definition.
Vinko Erceg, Broadcom Corporation

6. September 2007
Discussion: Cont’
In the CSI feedback case average SNR is well represented by dB value of the linear average since it represent average SNR in the Rx chain (same as the current definition in the draft).
However,
In the compressed/uncompressed feedback case it is more accurate to use average of the SNR values in dB since SNR per stream (post-processing) better relates to the capacity equation and therefore better representation of MCS. In MIMO case capacity equation includes log( f(SNR) ). Therefore, average of dB values is a natural choice.
Vinko Erceg, Broadcom Corporation

7. Conclusion We propose the following:
September 2007
Conclusion
We propose the following:
In the CSI case average SNR is determined as a dB value of linear average.
In the compressed/uncompressed case average SNR is determined as an average of dB values.
Proposed text is included in 07/2400r2
Vinko Erceg, Broadcom Corporation