Greetings Mr. Enno:
As the name suggests,
adjacent channel power is the amount of power a
transmitter allows to "bleed" into the channel
just above and below it. Lower ACPs are always
better, because it means you are not as likely
to interfere with a co-existing system trying to
operate in the same frequency space.
is an illustration that uses co-existence of
Zigbee with WiFi. Bluetooth could also be added
to the picture because like ZigBee, it uses a
frequency-hopping spread spectrum scheme.