| Cognitive MIMO technology is a wireless transmission technology which combined MIMO technology with cognitive radio. The application of MIMO technology in cognitive radio networks can obtain more freedom, and can further improve the system throughput and spectrum utilization rate, also can be of further use of MIMO array gain, diversity gain, the multiplexing gain to improve the spectrum resource utilization rate in cognitive radio networks. It can also use MIMO’s beam-forming, pre-coding technology to fight against all kinds of interference in the network.Then in the process of information transmission which cognitive users opportunistically access the licensed spectrum for communication, the cognitive users cause interference to the primary user, the research of the third chapter is ensure that it can maximize the throughput of the cognitive users when the primary user’s transmission performance is normal. During this study, the receivers of both primary user and cognitive users can get the perfect CSI. The interference alignment is realized via the pre-coding design of primary user and cognitive users. The cognitive users’ transmitter uses two-level pre-coding design scheme, not only reduce the interference of cognitive users to primary user, but also guarantee the performance of cognitive users. In cognitive users’ transmitter, a pre-coding matrix is designed to align the interference caused by cognitive users to the idle space sub-channel, ensuring the cognitive user’s transmission performance at the same time.In cognitive MIMO communication system, for the interference between cognitive users, the fourth chapter puts forward the interference elimination algorithm based on time division multiplexing. During this study, cognitive users transfer in different time periods, in the case of ensuring the maximum throughput of cognitive system, each cognitive user can transfer in distributing own time period. Each time period is calculated by the method of the optimization objective function. In order to insure the better communication performance, "energy efficiency" will be introduced to measure. The simulation results show that when the SNR is less than 6d B, under the unit bandwidth, the throughput of cognitive system adopting the proposed algorithm in this paper can increase 0.5 bit/s, at the same time, the average energy efficiency increase.Consider the relay can expand broadband wireless network coverage, eliminate the blind spot and increase the advantages of the system capacity. the relay is added to assist cognitive user system’s communication. In this communication scenario, we studied the relay-assisted distributed interference alignment algorithms and the interference alignment algorithm for considering the throughput of cognitive users. The study of the fifth chapter shows that the throughput of cognitive users has significantly increased 0.2 bit/s under the unit bandwidth without affecting the primary user’s transmission performance by adding relay-assisted communications scene in the cognitive system. |
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