Abstract: This paper considers an OFDM-based cognitive radio scenario where primary users are the centralized communication system.Since there may exist great differences in the quality among the channels from the secondary transmitter to different users in the primary system，the interference power introduced to them by secondary users may be extremely unbalanced that some of them may suffer severe interference even be interrupted while others may only suffer minor interference.In order to guarantee the communication quality of each user in primary system，it considers the power allocation problem with fair protection of users in the primary system against the interference and its optimal solution is also derived.Numerical results show that the proposed algorithm can reach a good balance between the resource efficiency and the fairness of protection of primary users.

Key words: cognitive radio, Orthogonal Frequency Division Multiplexing（OFDM）, power allocation, convex optimization, dual decomposition, fair protection

摘要： 考虑了一个主用户为集中式通信系统的基于OFDM的认知无线电场景。因为认知用户的发送端到主用户的各个子用户之间的信道质量可能存在很大的差异，因而认知用户给各个子用户导致的干扰可能存在很大的不平衡，有的可能几乎没有受到干扰，而另外一些可能遭受到非常严重的干扰甚至中断。为了确保主用户中每个子用户的通信质量，考虑了基于对主用户中各个子用户公平性保护的最优功率分配的问题，它的最优解也被推导。仿真结果显示，提出的算法能够在资源（功率、频谱）的使用效率和对主用户各子用户保护的公平性之间取得良好的平衡。

关键词: 认知无线电, 正交频分复用（OFDM）, 功率分配, 凸优化, 对偶分解, 公平性保护