Clear channel assessment

This disclosure provides methods, devices and systems for clear channel assessment (CCA). In one aspect a device performs a first clear channel assessment (CCA) check on a primary subchannel of a channel having a total bandwidth greater than or equal to 40 megahertz (MHz), a plurality of subchannels of the channel collectively spanning the total bandwidth of the channel, the plurality of subchannels including the primary subchannel and one or more secondary subchannels, the primary subchannel and the one or more secondary subchannels each having a bandwidth of 20 MHz, performs, on each of the one or more secondary subchannels, a respective second CCA check, and transmits a communication on the channel based on a status of each of the primary subchannel and the one or more secondary subchannels that is based on the performance of the respective second CCA check or the first CCA check.