A radio receiver is arranged to receive radio signals. The radio receiver includes a tuner, which outputs an electronic signal representing radio waves received by the radio receiver; a correlator, which cross-correlates a predetermined signal pattern with the electronic signal, and outputs a correlation signal; and a clear channel assessment module. The clear channel assessment module determines when the number of peaks in the correlation signal, over a fixed time window, exceeds a threshold count value, and outputs a busy signal in response to determining that the number of peaks exceeds the threshold count value.