1. WWiSE Response to Written Questions
January 2005
doc.: IEEE /XXXXr0
March 2005
WWiSE Response to Written Questions
Date:
Authors:
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C. Hansen, Broadcom
C. Hansen, Broadcom

2. January 2005
doc.: IEEE /XXXXr0
March 2005
Abstract
Response from the WWiSE organization to written questions from the IEEE Task Group N for the March 2005 meeting.
C. Hansen, Broadcom
C. Hansen, Broadcom

3. March 2005
Question #1
[Tim Wakeley] Why not extend the 20MHz MCS in Tables 003, 004, 005 down to BPSK code rate 1/2?
One of the goals of WWiSE was to limit the complexity of our proposal. Thus, for data rates less than 54 Mbps in our proposal, a station can employ either a legacy .11a/.11g mode or an optional 40 MHz 1 stream or 20 MHz 1 stream STBC mode.
C. Hansen, Broadcom

4. March 2005
Question #2
[Tim Wakeley] What is the range difference at 2.4 and 5.3GHz between 2x2 Nss = Mbps and STBC Nss=1 6.75Mbps?
WWiSE has not defined a 2 stream 6.75 Mbps mode and we have not explored the performance of such a mode.
C. Hansen, Broadcom

5. Question #3 [Tim Wakeley] What is the range difference between:
March 2005
Question #3
[Tim Wakeley] What is the range difference between:
11a with 2-RX ML chains 6Mbps and 2x2 Nss = Mbps?
11g with 2-RX ML chains 6Mbps and 2x2 Nss = Mbps?
WWiSE has not defined a 2 stream 6.75 Mbps mode and we have not explored the performance of such a mode.
C. Hansen, Broadcom

6. March 2005
Question #4
[Tim Wakeley] I would like to understand the difference in typical throughput of legacy 11g devices and overall BSS performance under the following conditions:
11n Greenfield mode with RTS/CTS protection for 11bg
11n Mixed mode preamble
WWiSE is working on this and will have some results soon.
C. Hansen, Broadcom

7. March 2005
Question #5
[Tim Wakeley] Since most if not all WWise 11a and 11g devices on the market today exceed the RX minimum sensitivity levels listed in Table 021 and 2-RX ML should do much better, why not recommend values that will guarantee a better minimum quality? How about separate tables for 1,2,3,4 antenna receivers?
WWiSE used the a and g amendments as guidelines for the values we specified in Table These are intended as minimum values to insure interoperability. In many applications, better performing devices may be employed. We welcome input from the n body on the minimum sensitivity for n devices.
C. Hansen, Broadcom

8. Question #6 [Tim Wakeley] 20.3.10.3: Why not increase CCA sensitivity?
March 2005
Question #6
[Tim Wakeley] : Why not increase CCA sensitivity?
WWiSE used the a and g amendments as guidelines for the CCA sensitivity. This is intended as minimum values to insure interoperability. In many applications, more sensitive devices may be employed. We welcome input from the n body on the minimum sensitivity for n devices.
C. Hansen, Broadcom

9. March 2005
Question #7
[Tim Wakeley] Preamble testing on legacy devices: when will data on Cisco radios be available?
Contribution /XXXXr0 contains our latest legacy preamble interoperability measurements. We are continuing to test devices and welcome input from other companies.
C. Hansen, Broadcom

10. March 2005
Question #8
[Tim Wakeley] In the case of devices with one antenna and STBC, please explain how 2 pilots are adequate.
The WWiSE design goal for the 20 MHz modes was to provide pilot performance that would be as good as a. This is described in detail in contribution r1. Specifically, the conclusion:
“If one decides to not fully comply with the mandatory modes by, e.g., designing a 2  1 system, the 11a pilot processing can still be outperformed when the pilot processing for the WWiSE pilot mapping is averaged over two symbols.”
C. Hansen, Broadcom

11. March 2005
Question #9
[John Benko] Seeing that advanced coding is very modular in the system design do you think the advanced coding scheme should be selected separately?
WWiSE believes we have a very competitive advanced coding option as part of our proposal. However we would follow the will of the n body if this was their choice.
C. Hansen, Broadcom

12. March 2005
Question #10
[John Benko] Accurate complexity estimates are a necessary criterion for proper advanced coding selection.  When will you provide such information to the group?
A variety of encoding/decoding architectures have been implemented for LDPC codes. The choice any one architecture is beyond the scope of an n proposal.  WWiSE has adopted an LDPC code that allows for a Layered Belief Propagation design, which lends itself to low-complexity implementation.  While it is difficult to agree upon accurate, verifiable complexity estimates for all the possible codec architectures, we welcome input from the n body on metrics to assess the complexity of the advanced coding solutions under consideration.
C. Hansen, Broadcom

13. March 2005
Question #11
[John Benko] In the WiFi market, there is a constant push to get certified products out as fast as possible.  How do you rationalize your position to include in your proposal a technology such as LDPC codes, with unclear implementation and complexity, especially when there are equal, if not better, solutions available with well-defined implementations?
WWiSE considered many different coding options for its advanced code for n and found that a LDPC code was the best choice.
C. Hansen, Broadcom

14. March 2005
Question #12
[John Benko] Due to the prolific research in the last few years within the field of LDPC coding there have been many patents filed; up to 152 have been found at the website since March Are all proprietary parts of your LDPC code covered by LOAs that have been accepted by the IEEE?
All the member companies of WWiSE have agreed to provide Letters of Assurance to the IEEE for n.
C. Hansen, Broadcom

15. March 2005
References
C. Hansen, Broadcom