Systems and techniques relating to wireless communications are described. A described technique includes monitoring wireless communication channels, including a first channel and a second channel, to produce a monitoring output, determining a first transmission period for the first channel by applying a first waiting period duration and a second waiting period duration to the monitoring output, determining a second transmission period for the second channel by applying the first waiting period duration and the second waiting period duration to the monitoring output, causing, based on the first transmission period, a first transmission on the first channel to reserve the group of wireless communication channels; causing, based on the second transmission period, a second transmission on the second channel; and monitoring, after the end of the first transmission period, for an acknowledgement(s). An end of the second transmission period can be aligned with an end of the first transmission period.