认知无线电网络MAC接入性能分析

Access performance analysis of MAC in CR network

认知无线电网络中授权用户享有频谱的优先使用权,一旦授权用户出现认知,用户必须中断正使用的频谱,造成正在传输的MAC帧丢失,认知无线电网络直接采用现有的IEEE802.11 DCF协议,无法解决由于中断引发的认知用户MAC帧丢失问题,当认知用户再次获得频谱接入机会时,将重新竞争接入,导致频谱切换延时较大.为解决该问题,本文改进了IEEE 802.11 DCF协议,提出增加冻结缓存机制,以此解决用户信道切换的延时较大问题.当无线链路出现中断时,改进的DCF协议通过冻结节点,中断当前计时器并缓存当前状态信息,认知用户和基站之间链路一旦恢复则继续传输中断前的MAC帧,从而避免了认知用户的重新竞争接入.仿真结果表明改进的DCF协议在频谱切换时能增大接入吞吐量,减小接入延时,提高了DCF机制在认知网络中的应用性能.

The Primary Users（PUs） has the right to use the spectrum in CR（Cognitive Radio） network,the CR user will have to make way the using spectrum once detecting the PUs,which makes the MAC frame loss,the existing IEEE 802.11 DCF protocol can＇t solve above problem about the losing MAC frame in CR network,CR users will have to re-access when getting the spectrum again,which leads to bigger delay of spectrum handoff.To solve the delay of spectrum handoff,this paper increases freezing and buffer mechanism by modified the existing IEEE 802.11 DCF protocol for CR network.The modified DCF protocol can continue previous MAC frame rather than afresh access by freezing the backoff timer and preserving the current state in the buffer.The simulation results indicate that the modified DCF protocol can increase the throughput and decrease the delay of access during spectrum handoff,which improves the performance of DCF mechanism in CR network.