Abstract: A method and device for adjusting contention window value adaptively are disclosed. The method comprises the following steps: the number n of stations participated in a contention currently is measured; according to the number n of stations participated in the contention currently, a practical collision probability Pc of a current contention window value CWold and optimal collision probability Pcopt, under the maximum network throughput are acquired; when a data frame is sent successfully, an initial contention window value CWinit is adjusted according to the practical collision probability Pc and optimal collision, probability Pcopt; when a data frame is sent unsuccessfully, a retransmission contention window value CWnew adjusted according to said practical collision probability Pc. The above solution can better reflect network collision situation, adaptively adjust an initial contention window value and retransmission contention window value jointly.

Abstract: A method and system for requesting a Physical PMCH are provided. The method includes: user equipment determines a target cell to be immigrated which is adjacent to a cell where the user equipment is located; and if the user equipment judges that a preconfigured Multicast Broadcast Single Frequency Network (MBSFN) area in the adjacent target cell does not comprise the MBSFN area used by the Multimedia Broadcast Multicast Service (MBMS) service/group call currently received by the user equipment, the user equipment requests a network side equipment to allocate a PMCH for the currently received MBMS service/group call. According to the technical solution provided in the present invention, the service continuity of the PTT communication user in a receiving state during the moving process is implemented.