Extracting narrow-band ZigBee signals(4 MHz) from a wide-band WiFi signal(20 MHz)? I am planning the following.

First sample the 20 MHz WiFi channel (WiFi channel-1 in figure).

Put band pass filters (5 MHz wide) around each of the ZigBee center frequencies (11, 12, 13, 14).

Re-sample the chunks to 4 MHz.

Is there anything wrong with this approach ?
Put band pass filters (5 MHz wide) … Re-sample the chunks to 4 MHz.


Don't do that! If you reduce the sampling rate to 4 MS/s, you need to filter to 4 MHz bandwidth anyway. So you could instead just use 4 MHz wide filters and get rid of the resampling filter.