A communication device performs a backoff procedure for a duration of time to determine whether a first sub-channel of a communication channel and a second sub-channel of the communication channel are available for transmission by the communication device. The first sub-channel is designated as a primary channel and the second sub-channel is designated as a secondary channel. Performing the backoff procedure includes using a single backoff counter, and starting and stopping the backoff counter based on sensing the first sub-channel and sensing the second sub-channel.