Calculating theoretical datarate for 802.11 standards

[Tjvelcro]

Hi all,

I need some help finding the thoeretical data rates for 802.11 a, b, g, n standards. I think I should use the following equation...

C = 2Blog₂M

C = data rate in bps, B = channel bandwidth in hz, M = # of voltage levels or # signal elements

For instance I look up the channel bandwidth for 802.11a and find its 16.6Mhz (20Mhz total) and its modulated with BPSK so its # of signal elements is 2. After I put them into the formula above I get...

C = 2(1660000)log₂2 = 33200000 = 33.2Mb/s

Which is way to high according to http://en.wikipedia.org/wiki/802.11a it should be around 12Mb/s. Anyone have any ideas on what could be the problem? Thanks for reading!

Tjvelcro

 

[Coin]

Mb not MB right?

So it looks like you're just giving the maximum bandwidth for an 802.11 transmitter, right? But the real protocol won't attain that maximum or I expect even get anywhere near. There is overhead to the protocol. 802.11 will afaik not saturate the entire 802.11 band but rather must share the air with other 802.11 devices and indeed other devices of totally different types. All this stuff will tend to cut down on how much you can exploit the band. And 11g and 11n do have a much higher maximum data rate than 11a. It looks to me like there is not anything wrong with your calculation but rather it may be you are calculating something different from what the "official" 802.11 maximum data rate is trying to represent.

Have you looked at the 802.11 standards (they're linked from the wikipedia page on 802.11)? Maybe they contain discussion of how the data rate number is reached.

 

[Tjvelcro]

Sorry for the late reply...

Oh ok that makes sense there are many factors that could be effecting the potential for the datarate to reach that high. I will probably explain that in my work. Any idea about 802.11b which uses CCK (Complementary code keying) what M value to use? Thanks!

Tjvelcro