In Long Term Evolution (LTE) systems, when uplink data needs to be transmitted, an uplink scheduling request (SR) mechanism is adopted by a user equipment (UE).  By sending the uplink scheduling request to a base station, the UE informs the base station that the UE needs uplink resources for data transmission.  After receiving the scheduling request from the UE, the base station allocates resources to the UE, and the UE performs data transmission on these allocated resources.  However, the mechanism results in a large amount of signaling overhead. 
In order to solve the problem, data transmission may be performed based on contention.  That is, the UE does not need to request the base station to allocate resources for data transmission by the scheduling request, but randomly selects resources from a resource pool for data transmission. 
For data transmission performed based on contention, the selection of resource has an important impact on the whole communication performance.  Therefore, how to select appropriate resources is an urgent problem to be solved in technologies of data transmission based on contention.