Forum

In the "Spread Spectrum Technology" chapter
under
Comparing 802.11 Technologies
Co-location
802.11b DSSS vs. 802.11g OFDM

it states that 802.11b and 802.11g use the same channel numbers and roughly the same frequencies (the center frequencies are the same, but the channel widths are slightly different).

Are the channel widths different? I read the appropriate clauses but could not find the channel width in 802.11g. Could someone point me to it?

Thanks

Hi Moe:

IEEE 802.11 19.1.2: The ERP PHY (802.11g) "uses the 2.4 GHz frequency band and channelization plan specified in 18.4.6."

CWNA Study Guide v3 page 210 last paragraph would be more correct if it began -- "DSSS, HR/DSSS (802.11b), and ERP (802.11g) use the same channel numbers and roughly the same frequencies (the center frequencies are the same, but the channel separation requirements are slightly different)..."

Two DSSS channels need to be six channels from center to center to not "interfere". The others need to be five channels from center to center to not "interfere". See 15.4.6.2 and 18.4.6.2. And this is despite the fact that the transmit spectrum masks for the three PHYs are identical. Go figure.

I hope this helps. Could you add your location to your forum profile? Thanks. /criss

Criss_Hyde,

Thanks for the reply..that helps. Just to confirm then, DSSS requires 30 MHz between channel centers and HR/DSSS & ERP require 25 MHz between channel centers.

moe

Right.