In a communication system having a plurality of user equipment (UE) devices that are operating in a contention based mode for device-to-device (D2D) communication, each UE device transmits a preferred transmission indicator when a condition for preferred transmission is met at the UE device. If a UE device receives a preferred transmission indicator, the UE device delays transmission of a D2D scheduling assignment (SA) to contend for communication resources for D2D communication. The length of the delay can be based on a number of preferred transmission indicators that are received. The preferred transmission indicator is based on a buffer size in one example.