I have some questions on WiFi channelization in 802.11n and 802.11ac. Here is the snip of List of WiFi channels (source: WiKi):

enter image description here

I am working on the L1 layer for 802.11n and 802.11ac model where I am transmitting and receiving some WiFi packets


  1. Transmitting and Receiving WiFi Packets on 20MHz channels is pretty straight forward. If I want to use 40 MHz channel (Channel 38) , I need to do channel bonding, where channel 36 and Channel 40 are used.
    Is the centre frequency going to be 5190 (channel 38) ? If that's the case, why we even bother to use the term primary and secondary channels?
  2. What about the reception side? Do I need to tune my Rx to Channel 38 with samplerate > 2·40 MHz, or do I need to use any of the primary and secondary channels?
  1. Your receiver does not know what BW you are using. Hence it will always be tuned to receive 20MHz BW (ch 36 or 40). So for the preamble part you need to transmit in channel bonding (2 x 20MHz) mode. Once the receiver has detected preamble it decodes the header to find out that data part is 40MHz. You need to turn on a bit in header for this (forgot the exact bit number) you can find it in standard. Same case for 80MHz BW. Preamble part is 4 x 20MHz.

  2. Yes you need to continuously tune to 20MHz channels in the receiver. Otherwise no way of knowing what BW transmitter is sending. For fast synchronisation this is the feasible method. Once you detect preamble you need check for that header bit in both primary and secondary channels to check for 40MHz BW.

| improve this answer | |
  • $\begingroup$ Thanks, jithinrj.. I kind of understand now. Let me get a spec analyzer with a client and acces point to check it out. Thanks again $\endgroup$ – Saira Mar 10 at 18:17
  • 1
    $\begingroup$ Hi jithinrj,, Thanks for explaining. I took a spec analyzer with a WiFi client and Access point and checked and tried to see it.. It helped to understand it better $\endgroup$ – Saira Mar 11 at 0:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.