A method is provided for controlling access to a wireless communications medium. The method includes: sampling RF activity on the medium; autocorrelating samples to produce a first value indicative of autocorrelation computed with a first delay substantially matching periodicity of a signal of interest and to produce a second value indicative of autocorrelation computed with a second delay different from the first delay; monitoring the first value to determine whether the first value is possibly indicative of the signal of interest; monitoring the second value to determine whether the second value is indicative of an interferer signal; and preventing transmission of an RF transmit signal on the medium in response to the first value indicating that activity on the medium includes the signal of interest when the second value indicates that activity on the medium does not include an interferer signal.