In the orthogonal frequency division multiple access (OFDMA)wireless broadband networks ,the efficiency of ran-dom access can be improved by distributing contention onto multiple channels .However ,due to the multichannel property ,the tradi-tional systems based on request-to-send (RTS )control frame have to encounter the idleness of subchannel ,the extension of RTS transmission time and the complex synchronization of uplink communication .To solve these problems ,in our scheme ,the users send signals on random subcarrier to request transmission opportunity .The access point senses these request signals ,and determines which user is permitted to access channel according to the busy state of the subcarriers .The theoretical analysis and simulation results both show that our scheme outperforms the traditional RTS-based schemes in term of the throughput .%在基于正交频分多址技术的宽带网络中，通过把竞争分散到多个子信道能有效改善随机接入的性能。然而多信道特性也会使传统基于Request-To-Send （RTS ）控制帧的随机接入协议面临子信道空闲、RTS传输时间延长、上行复杂的问题。针对这些问题，在本文所提出的接入方法中，用户在没有被分配到资源时通过在随机子载波上发送信号来请求传输机会，与此同时，接入点对这些信号侦听，并根据子载波忙闲状态确定哪些用户可以接入。理论分析及仿真结果表明，相比传统依靠RTS的接入方法，采用子载波侦听，系统将获得更高的吞吐量。
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