| With the rapid development of wireless communication and mobile communications, more and more users want to occupy spectrum resources, and the spectrum resources are increasingly scarce. Cognitive radio is a new method, which is introduced to wireless communication. The limitation of the frequency resource can be fit well and the efficiency of spectrum resources can be improved. As the fading characteristics of the wireless channel, sometimes the communications of network may be interrupted. In response to fading characteristics of wireless network, relay nodes are introduced to assist the transmission of wireless network. In cognitive relay network, the cognitive users work as the relay of the primary network to help the transmission, while transmitting the cognitive information in an appropriate manner. Cognitive user is used as a relay, which not only improve the performance of the primary network, ensure the QoS of the primary network, but also cancel the fixed relay nodes to save the cost. The use of relay in cognitive radio network is meaningful. The beamforming technique is utilized in cognitive relay network, which improves the performance of the communication system without increasing resources. In this article, firstly, distributed relay beamforming models of the traditional network are summarized and simulated. Secondly, distributed relay beamforming models of the cognitive network is studied. In this scenario, the cognitive users serve the primary network, at the same time they send the cognitive information to the cognitive base station. The problem of relay power minimization under the SINR constraints of receiving terminal is analyzed. Using of convex optimization theory, a second-order cone optimization algorithm is proposed, which is more efficient than traditional algorithm. Then compare the performance of the two algorithms. By studying the parameters of the optimization problem, the factors who affect the beamforming gain are analyzed. |
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