1. On Channel Spacing for 2.4GHz
July 2006
doc.: IEEE /xxxxr0
July 2006
On Channel Spacing for 2.4GHz
Date:
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David Tung, Ralink
David Tung, Ralink

2. Summaries of Related Comments
July 2006
Summaries of Related Comments
CIDs 3010, 11566, 6768, 7282, 12111, 1728, 4570, 7871, 3373, 286, 705, 3602, 7312, 7925, 1558, 258, 3501, 10380, 3471, 1560, …
Summaries of comments - 40MHz HT device is a bad neighbor. There are three clusters of suggested resolutions,
Forbid 40MHz mode in 2.4G
25MHz channel spacing
Scan collision-free 40MHz channel before using (referred CID index with red).
David Tung, Ralink

3. What Was Missing from 25MHz Analysis
July 2006
What Was Missing from 25MHz Analysis
Ensemble average indicates asymptotic performance, but performance with practical AP numbers is not known. (Refer /869r1)
Dynamic channel allocation is not evaluated, which will be important for future TGn channel selection.
Case study: given a number of sampled APs with the distributions of some deployed APs, find the channel collision rate. (Channel collision means CSMA/CD can not be applied here.)
David Tung, Ralink

4. Results Based on US AP Distribution
July 2006
Results Based on US AP Distribution
David Tung, Ralink

5. Results Based on Europe AP Distribution
July 2006
Results Based on Europe AP Distribution
David Tung, Ralink

6. July 2006
Conclusions
Fix 1, 6, 11 channel with 25MHz channel spacing can not resolve the 40MHz channel collision issue.
Dynamic channel allocation that always fall back to 20MHz when 40MHz collision happens can resolve the 40MHz channel collision issue, independent of 20MHz/25MHz channel spacing.
Dynamic channel allocation can also be used to avoid 20MHz channel collision.
David Tung, Ralink

7. Dynamic Channel Allocation Algorithm
July 2006
Dynamic Channel Allocation Algorithm
There are two channel modes: 40M/20MHz mode, channel collision and collision free mode.
Periodically scan channels and update channel collision mode.
If under 40MHz mode and current channel selection has collision, select next mode according to the order 1) 40MHz collision-free 2) 20MHz collision free 3) select preferred 20MHz collision mode.
If under 20MHz mode and collision free, select next mode according to the order 1) 40MHz collision-free 2) no change.
If under 20MHz mode and current channel selection has collision, select one mode according to the order 1) 40MHz collision-free 2) 20MHz collision free 3) no change.
If under 40MHz mode and collision-free, stays unchanged,
David Tung, Ralink