one or more wireless communication systems may coexist at about the same geographical location and be configured to access the same radio channel . the coexistence of these systems may cause collisions and degrade throughput . although countermeasures , such as reserving airtime with a resource assignment , may be taken to avoid collisions , these countermeasures are degrading throughput as well . the reserved airtime is reduced by adding a start time to the resource assignment . the reduced airtime may be used by others for performing a transmission , thus increasing the throughput and efficiency of the access to the radio channel .