Techniques are described for contention-based wireless communications channel access that may improve the likelihood that a contention procedure will pass and allow a device to transmit an uplink or downlink transmission using the contention-based channel. Various disclosed techniques may determine a transmit power for a subsequent transmission based on channel characteristics during one or more clear channel assessment (CCA) time durations. The transmit power may be selected to provide a CCA threshold that may increase the likelihood that a device will win contention for the channel during the CCA procedure.