Research On Multiuser-diversity-based Interference Alignment In Cognitive Radio Networks

In recent years, as an intelligent dynamic spectrum access technique, cognitive radio has caused widely attentions and investigations to solve the spectrum scarcity problem in wireless communication system. In cognitive radio network, cognitive user can adaptively choose transmission parameters to opportunistically access the licensed spectrum so as to improve the spectrum efficiency. Cognitive radio stipulates that the total interference power from all the cognitive users must be under a certain threshold, which strictly restricts the numbers of accessed cognitive users. Thus, in order to further improve the spectral efficiency, the multiuser diversity based interference alignment technique has been applied to the cognitive radio network to effectively eliminate the mutual interference while guaranteeing the quality of licensed user and maximizing the throughput of the cognitive network. Consider that the green communication is growing more important, power allocation is combined with the multiuser diversity based interference alignment network to further improve the spectral efficiency and the energy efficiency.The contributions of this paper are mainly as follows:(1) First, the SINR decrease problem of the received signal after interference alignment processing is quantitatively analyzed. Then, this problem is explained through comparing with MIMO system By taking advantages of the multiple cognitive users, a multiuser diversity based interference alignment technique is combined to the application to the spectrum sharing in cognitive radio network. This algorithm can eliminate the mutual interference effectively, guarantee the quality of service of licensed user, and allow more cognitive users get the opportunity to access the spectrum.(2) Consider that the numbers of cognitive users are dynamically changing, two models targeted at different scenarios are proposed:in the S>Q model, OIASO and OIAT algorithms are proposed, the communication quality of licensed user is guaranteed and the cognitive network is optimized.. In the S≤Q model, there are less cognitive users. IAUS and IAUAS algorithm are proposed to totally improve the licensed user’s transmission rate.(3) In practical wireless communication scenario, the channels are asymmetrically fading, thus, the chances to access the spectrum among the cognitive users are unbalanced. Thus, the proposed algorithms are revised to maintain the fairness among the cognitive users.(4) The power allocation in the multiuser diversity based interference alignment network is studied, to further improve the network’s spectral efficiency and energy efficiency. Simplified algorithms are proposed to reduce the computational complexity with a little performance loss.