802.11b/g Wireless Bandwidth

2007-11-13T23:28:00.000-08:00

After my last move to a new apartment I found myself dealing with a severe wireless bandwidth problem. The bandwidth between my wireless clients and the wireless access point varied dramatically ranging from 2Mbps to 54Mbps. After a bit of investigation it became clear that the problem was the other ~20 wireless access points (some of them performing channel hopping) operating in the same spectrum (802.11b/g). The underlying problem was packet loss caused by the severe interference around.

The access point waits for an ACK after the transmission of a frame within a time interval before declaring the packet lost and therefore reducing the transmissions rate. Note that the value of this timeout interval determines the physical distance in which the access point can operate (the larger the value of the timeout, the higher the range). In typical access points this value is preset to something very large - the manufacturers probably assume typically a low level of interference.

I am using a Linksys WRT54G (v.3) running DD-WRT (v.23 SP2) and the ACK timeout can be controlled from the management console. It is expressed as a sensitivity range (the actual name is 'Sensitivity range (ACK timing)' ) in meters with the default value of 2000. If you live in a small apartment like I do and not on a large ranch, a value much smaller than 2000 will do. In my case, reducing this value to 250 meters proved quite beneficial for the overall transmission rate of the access point. The rate would no longer drop bellow 11Mbps and would often be around 36-48Mbps.

Note: I am a heavy wireless user and because I could still not tolerate the variations above (which would do just fine for an average user) I finally ended up adding a 802.11a access point to my network. I am getting reliable 54Mbps rates now, but the details about my setup will come in another post.

Dan's Tech Corner

802.11b/g Wireless Bandwidth