A system including an activity sensing module to sense RF activity in first and second sub-channels of a communication channel of a first wireless network. N adjacent channel interference (ACI) filter modules arranged in parallel receive signals from N antennas, respectively, filter out signals in channels adjacent to the communication channel, and generate N filtered signals, respectively, where N>2. The activity sensing module generates control signals based on the N filtered signals. A channel identification module processes the control signals, and determines that both of the first and second sub-channels are available when the RF activity originating from a second wireless network is not present in both of the first and second sub-channels, and that the first sub-channel is available when the RF activity originating from the second wireless network is present only in the second sub-channel and is less than or equal to a predetermined threshold.