Research On Relay Selection And Power Allocation In Cognitive Radio Networks Based On Public Relay

With the progress of the Internet and information technology, variety of wireless communication devices have appeared in large numbers, and different wireless communication service is expanding at an astonishing rate, making the radio spectrum resources become increasingly strained. So how to improve the utilization of radio spectrum at a fixed spectrum allocation policy becomes the key constraint for the development of wireless communications.Cognitive radio technology enables cognitive users to dynamically detect spectrum holes and opportunistically access the authorized spectrum to perform cognitive communication, as long as it doesn’t affect the normal communication of authorized users. This technology can improve the utilization of radio spectrum. By using cooperative relay nodes in wireless communication, the cooperative relaying technology can achieve the effect of virtual MIMO, and expand the coverage of the wireless communications while improving the communication quality of the users who are located at the edge of wireless cell and the users who are in the coverage blind area. The combination of these two techniques can improve the utilization of wireless spectrum resource and the overall performance of wireless communication system, so this paper establishes a cognitive communication system model based on cooperative relaying, mainly to study the following:In order to effectively control the interferences between the primary user and secondary user in the cognitive radio environment based on underlay spectrum sharing, in this paper, the cooperative relay with cognitive ability will be further expanded into a public cooperative relay. The public cooperative relay can control both the primary and secondary users’signal relaying. The system can reasonably allocate the transmit power of each node based on the primary user’s communication requirements and the channel state information, and improve the utilization of wireless spectrum by allowing the secondary user opportunistically access the spectrum to perform cognitive communication. The destination node combines the source signal and the relaying signal with MRC method to obtain diversity gain, so the performance of the wireless transmission system can be further improved.Specifically, this paper establishes a public relay communication model based on cognitive radio system, and analyzes the transmission process of the system in both AF and DF relay mode. On the premise of not affecting the primary user’s normal communication, and in order to maximize the secondary user’s communication rate, this paper proposes a relay selection and power allocation optimization scheme through the method of convex optimization theory. The simulation results showed that the proposed power optimization scheme not only effectively improve the utilization of the radio spectrum, but also increase the performance gain of the system.