Research Of Interference Alignment Algorithms In Cognitive Radio

In recent decades, with the explosive growth of wireless communication and the lack of spectrum resources, the interference between wireless devices is increasing seriously, which affects the performance of the wireless communication system. Therefore, how to deal with interference between the users effectively has become an important research topic.As a new interference management method, interference alignment can compress the interference signal space and improve the degree of freedom(DoF), then much attention has been paid to the interference alignment. The achievement of interference alignment is by using pre-coding matrix and post-coding matrix. At transmitter the pre-coding matrix isolates the desired signal and the interference signal from each other in space, time, or frequency domain. The post-coding matrix at receiver minimizes the effects of the interference and the noise.The topic in this thesis comes from the National Natural Science Foundation project undertaken by my supervisor. The major efforts of this thesis are focused on interference alignment algorithms in cognitive radio. Firstly, we introduce the related background information, technical principle, feasibility analysis and some classical interference alignment algorithms, then we propose a dual-layer pre-coding interference alignment scheme in a multiple input multiple output(MIMO) cognitive radio system which includes one primary user and K secondary users. The minimum mean square error(MMSE) of the primary user is guaranteed, at the same time, the first layer pre-coding matrix allows the secondary users to share the same spectrum resources of the primary user without generating any interference to the primary user, thus improving the spectrum efficiency of the system. The second layer pre-coding matrix assures the interference between the secondary users is aligned. The numerical results show that, comparing with conventional interference alignment schemes in cognitive radio system, a higher capacity of the secondary users is achieved.