机会频谱接入是提高频谱利用率，解决未来无线通信频谱资源危机的有效途径。项目利用OFDM子载波分集性，将频谱感知与频谱接入相结合，研究基于OFDM实现的认知无线网络机会频谱接入理论与方法。分析子载波频域特征，探索频谱感知与子载波接入新机制，解决频谱感知与频谱接入在时域上的冲突问题；以历史频谱信息为基础，分析频谱接入规律，研究频谱感知与子载波接入预测模型，优化设计感知子载波与接入子载波，实现网络认知增益最大化；分析不可信认知节点对协作感知的影响，研究节点可信度新度量，实现协作检测全局判决门限自适应，消除不可信节点对协作感知的影响；分析网络动态子载波优化分配与传输策略，探究子载波能量有效性与上、下行链路子载波配对的内在联系，最优配对上、下行链路子载波；研究频谱交易中的利益因素，构建具有记忆功能的代理商频谱需求函数和利益函数，提高认知网络效用。其研究成果可为网络机会频谱接入提供理论依据和技术支持。

Opportunistic spectrum access is an effective way to improve the spectrum efficiency and solve the spectrum resource crisis in future wireless communications. According to the diversity of subcarriers in the orthogonal frequency-division multiplexing (OFDM) transmission, this project addresses the opportunistic spectrum access in the OFDM-based cognitive wireless networks by combining spectrum sensing with spectrum access. Based on the spectrum characteristic of subcarriers, a new mechanism will be designed to carry out spectrum sensing and spectrum access simultaneously and avoid the collision of primary user and secondary user. Ground on the historical information of spectrum usage, the prediction model for spectrum sensing and subcarriers access will be established to distribute the sensing subcarriers and access subcarriers optimally and achieve the maximum cognitive gain in the OFDM-based cognitive wireless networks. In order to eliminate the effect of uncreditable cognitive nodes on the cooperative spectrum sensing, a new measure of creditability of cognitive nodes will be investigated. It will be used to optimize the global adaptive decision threshold in fusion center. When analyzing the dynamic subcarriers allocation and transmission strategy, the internal relationship between energy efficiency of subcarriers and subcarriers pairing will be studied to pair the subcarriers of uplink and downlink optimally. From the view of economy, the spectrum demand function and the profit function with memory will be established to improve the efficient utilization of available frequency bands. The research findings may provide theoretical basis and technical support for the opportunistic spectrum access in cognitive networks.