On Spectrum Sensing And Sensing-based Spectrum Sharing In Cognitive Radio

As the development of wireless communication technology and the rapid growth of wireless appli-cation, most of the available spectrum resource has been allocated. Cognitive radio (CR) is a providing technology to relieve the scarcity of spectrum resource. The key concept of CR is described as follow: On the basis of spectrum sensing and identification, the cognitive user opportunistically access the idle spectrum in an appropriate mode, subject to the constraint of interference on the licensed users. And then the spectrum reuse and sharing is achieved. In the thesis, the spectrum sensing in PHY layer as well as MAC layer is studied. Furthermore, sensing-based spectrum sharing in the multi-antennas scenario is also discussed thoroughly. The work of this paper is summarized as below.The background, concept and functionality of cognitive radio is introduced in chapter 1. An overview of interference temperature and spectrum sensing is given firstly, then the spectrum sharing and spectrum management is described. Next, the research progress in cognitive radio, including theo-retic aspect, standarization progress and application prospect, is formulated.The spectrum sensing algorithm in CR is briefly reviewed at first. A spectral entropy based primary user detection algorithm is proposed. The algorithm increases the detection performance in low SNR condition at the cost of more computational complexity. The performance of the proposed algorithm is simulated and verified.A cooperative spectrum sensing scheme based on two round cooperation is proposed. Exploiting space diversity and multi-user diversity, cooperative sensing can conquer the fading and shading problem of radio channel. Under constraint of control channel bandwidth, the proposed method is more flexible than the traditional method and achieves the tradeoff between sensing performance and cooperation overhead.A cluster based active sensing algorithm is proposed in cognitive ad hoc radio networks(CRHAN). It fully exploit the locality of ad hoc transmission, and utilize the in-active secondary users in the adjacent cluster to perform active sensing. Although the interference in the edges of cluster can not be eliminated, the calculation shows the false probability caused by the interference is acceptable, specially when the cluster size is appropriately designed. The performance of different SU position distribution model is evaluated by Monte-Carlo simulation method.Multiple antenna technology is widely used to improve system capacity and control interference between different users. In CR context, MIMO system provides new opportunistic access dimension for secondary users. In chapter 5, a spectrum sharing strategy based on spatial-temporal sensing is proposed:the temporal sensing is first performed and the SU access the spectrum if the detector indicates that the PU is not active, otherwise the SU adapts its access strategy including transmission power or beamforming vector to alleviate the interference to the PU. The optimal precoding matrix aim-ing to minimize the average MSE is formulated and solved numerically under different sensing schemes.