分布式天线系统中PCF MAC协议的重传性能优化

摘要

To solve the serious collision under high user density conditions,this paper studies the perform-ance of IEEE 802. 11 Point Coordination Function(PCF) when applied to the distributed antenna system. The relation between the retransmission times and the parameter CFPPeriod ( Contention Free Period Peri-od) of Beacon frame is analyzed while the ratio of CFPMaxDuration( Contention Free Period Max Duration) to CFPPeriod is kept constant. Considering from the aspect of adjusting Beacon interval to improve retrans-mission performance,how the parameter CFPPeriod influences the fairness among stations and the traffic density of network is also analyzed. The OPNET simulation results validate the result that as CFPPeriod keeps increasing,the transmission time increases first then starts to drop,when the ratio of CFPMaxDuration to CFPPeriod is kept constant. The result indicates that when CFPMaxDuration/CFPPeriod is 0. 5,choosing the parameter CFPPeriod among 0. 02~0. 04 s can ensure the fairness among STA(Station)and reduce the number of STA which is about to access the channel at the beginning of Contention Period(CP),so that transmission times can be reduced effectively.%为应对分布式天线系统在高用户密度场景下冲突严重的问题,研究了分布式天线系统结构中应用IEEE 802.11点协调机制(PCF)的媒体接入效率,分析了在保持信标帧中参数CFPMaxDura-tion(Contention Free Period Max Duration)与CFPPeriod(Contention Free Period Period)比例的前提下平均重传次数与CFPPeriod的关系。分析了CFPPeriod的变化对节点( STA)间公平性及网络流量密度的影响,考虑从改善重传性能的角度调节信标帧间隔CFPPeriod,并使用OPNET平台进行仿真分析,验证了在保持参数CFPMaxDuration与CFPPeriod比例的条件下平均重传次数随CFPPeriod的增大先减小后增大的结论。仿真结果表明,当固定CFPMaxDuration/CFPPeriod 为0.5时,在0.02~0.04 s之间选取CFPPeriod既能保证节点间公平性,也能减少在竞争阶段( CP)发送数据的节点数目,从而有效降低重传次数。