Cooperative Spectrum Sensing Technique Based On Orthogonal Waveforms Design In Cognitive Wireless Networks

Spectrum sensing is the key technology for cognitive radio (CR) because it is crucial for the success of cognitive radio and can guarantee the service improvement to unlicensed users and the avoidance of interference to licensed users. It has become a research focus in wireless communication field. This work is supported by projects like National Science Fund of China etc, and attempts to make a contribution to the theory and application of spectrum sensing.The work first studies the basic concept of CR and several common methods of spectrum sensing technology. On this basis, we make an exploration into the cooperative spectrum sensing technology by multiple CR users. The multi-user collaboration can improve the detection performance and lower the demand of the detection sensitivity and reliability for the individual user. Cooperative spectrum sensing needs a control channel for each CR user to report its sensing result, however, the control channel is usually bandwidth limited. Considering the practical bandwidth constraints, a novel cooperative spectrum sensing scheme based on orthogonal waveforms design is proposed in this work. Based on the principle framework of the transform domain communication system (TDCS), we employ the idea of spectrum coding and make good use of the orthogonality of OVSF codes in this scheme. By designing mutual orthogonal waveforms for different sensing bits, all the users are allowed to send their sensing information simultaneously on the same available band, without causing serious collision. In a CR network, therefore, our scheme can also greatly simplify the upper layer protocol design and reduce the communication overhead, hence significantly improving spectrum utilization and transmission efficiency.Furthermore, in view of the large system overhead in the process of cooperative spectrum sensing in large-scale cognitive wireless networks, we attempt to apply the orthogonal waveform-based cooperative spectrum sensing scheme into the clustering CR networks. In this work, the clustering model has been abstracted to hierarchical tree-structure. The nodes in each layer are allocated OVSF codes to obtain the orthogonal properties. Therefore, considering the bottom layer of the tree-structure, the CR users in the same cluster can simultaneously send their sensing bits to CH without collision in virtue of the favorable orthogonality; as for the CHs in the upper layer, each CH can send the aggregated information to CR base station at the same time as well. Performance analysis and simulation results show that the proposed scheme can significantly outperform conventional schemes on the improvement of the transmission efficiency, especially for large-scale CR networks with enormous users.