I have been learning about the WLAN technology and I couldn't understand the logic behind the choice of the Clear Channel Assessment thresholds protocol used in CSMA/CA:
In 802.11ac for WLAN, a device attempting to transmit over a 20 MHz subchannel should make sure the channel is idle. The threshold at which this device decides whether it should transmit or not is -82 dbm. If a device wants to transmit over primary 40 MHz channel the threshold at which it decides if it can or it can't transmit is -79 dbm (+3db wrt to -82 dbm because we doubled the bandwidth).
1) Why is that a 3db difference in threshold exists, there must be logical explanation for such?
I am just looking for some logical interpretation of why these concepts are made? Thank you