中文摘要：

基于次用户采用的不同分组层策略，分析了认知无线电网络的性能，提出了两种认知无线电网络模型，推导了次用户的丢包率、分组时延、吞吐量以及频谱利用率的表达式．同时通过认知无线电网络的性能仿真验证了理论分析模型的准确性．分析和仿真结果表明：分析模型能准确地评估认知无线电网络的性能；次用户的丢包率、分组时延和频谱利用率随着业务流流入速率的增加而增加；使用认知无线电技术能大大提高频谱利用率；次用户采用不同的分组层策略对频谱利用率的影响很小，而对吞吐量的影响很大．

英文摘要：

In this paper, the performances of cognitive radio networks with different packet level policies for secondary users are analyzed, and two models for cognitive radio networks are proposed to derive the formulas of packet loss ratio, packet delay, throughput and spectrum utilization for secondary users. Moreover, a performance simulation is carried out to evaluate the accuracy of the proposed theoretical models. Analysis and simulation results indicate that （ 1 ） the proposed models can accurately evaluate the performance of cognitive radio networks ; （2） the packet loss ratio, packet delay and spectrum utilization of secondary users all increase with the arrival rates of services; （3） cognitive radio networks help to improve the spectrum utilization remarkably; and （4） the difference in packet level policy of secondary users affects the spectrum utilization slightly but it exerts significant effects on the throughput.