| With the development of future wireless communications, it becomes more and more obvious that interference constraints the overall capacity of the system. So, interference management has drawn more and more attention. But the traditional methods cannot solve the problem effectively. Interference alignment has its own advantage and it stands out over other methods. Recent researches show that interference alignment is an effective interference management method and it can improve the Degrees of Freedom (DoF) of the system.Novel relay system has more efficient information processing capacity and it is the key technology of future wireless communication system. This paper studies the application of interference alignment in cognitive relay system. Using interference alignment, the system which includes one cognitive relay, three pairs of users and each node has M antennas, can get2M DoF. This is a great improvement compared to the3-user system whose DoF can reach3M/2. To improve the sum-rate of the system, this paper optimizes the precoding matrix which is deduced from interference alignment. This paper also considers the energy efficiency and gives a better power allocation matrix. The simulation results are shown at last.In the multi-cell system, the signals received by the users in the edge of the cell are weaker, which means they suffer severe interferences. In order to solve this problem, this paper proposes a relay-based scheme which uses interference alignment. The relay together with interference alignment can enhance the communication quality and manage the interferences. Therefore, this paper uses relay to acquire the overall channel state information and work out the precoding matrix, which can reduce the work load of the base station. In addition, this paper shows a decoding scheme which can help the relay solve out the signal quickly. Optimizing the precoding matrix is also in our consideration. At last, simulation results are given. |
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