Research On Transmission Performance Of Cognitive Radio User For Cooperative Cognitive Wireless Communication Systems

By the development of communication technologies, wireless communication users are increasing rapidly, the resource requirement of wireless spectrum increases accordingly. In that way, the resource used for wireless communication is becoming more and more lacking. For these reasons, it makes the resource of wireless spectrum be very valuable. Hence, how to enhance the capacity of wireless communication system and enhance the utilization of wireless spectrum are the important tasks for the research on term of wireless communication for a long time. For the lacking of the resource on wireless spectrum, the disadvantage of wireless communication is all the signals are transmitting in the same space, and these signals must be interfered by each other. In the wireless communication networks of many senders and receivers restricted by each other, how to reach the biggest communication rate between every senders and receivers is very important problem too. Cooperative communication technology is a virtual MIMO technology. Cooperative communication technology can get the cooperative spatial diversity gain by the virtual antennas array. With the advantage of diversity technology and relay communication technology, cooperative communication can make the performance gain in the traditional wireless communication networks. Cognitive radio can enhance the utilization of the wireless spectrum effectively by using the idle spectrum sufficiently through space and time dimension. Cognitive radio has the ability of sensing the environment around cognitive radio system. Cognitive radio can persisted sensing the licensed spectrum, and adapt the parameters on transmitter-receiver equipment to change the communication on the sensed spectrum. The communication performance of licensed user pair must not be changed, and the licensed user pair has the top priority to access the spectrum using by cognitive radio user pair. In this paper, based on the problem of how to enhance the performance of wireless communication system and how to use the wireless spectrum effectively, the problems on achievable rates for a relay-aided Gaussian interference channel, how to enhance the throughput of cognitive radio user pair in cognitive wireless radio system and how to allocate the power between the cognitive radio user pair and cognitive radio relay are researched. The major works are outlined as follows:1. In the two-user Gaussian interference channel, the performance of wireless communication system is enhanced by using cooperative communication technology. The problem on two-user Gaussian interference channel is still an open problem. In this paper, two system models on a relay-aided Gaussian interference channel are proposed. In the two-user of parallel communication interference channel, two-user share the common relay. The common relay works in the time-division duplex communication scheme and the amply and forward cooperative communication strategy is used by the common relay. Based on the two system models, the expressions on the relay-aided Gaussian interference channel are given separately. The upper bound and lower bound on achievable sum rates for a relay-aided Gaussian interference channel are given separately. Comparing with the achievable sum rate for Gaussian interference channel, the system performance of a relay-aided Gaussian interference channel is better than Gaussian interference channel without the help of relay.2. The throughput of cognitive radio user pair in cognitive radio system is enhanced by using cooperative communication technology. For resolving the problem on the lack of wireless spectrum resource, the system models on relay-aided Gaussian interference channel are extended combined with the cooperative communication technology. It assumes that one pair of the user pair in system model is licensed user pair, and the other pair of the user pair in system model is the cognitive radio user pair. The common relay helps the licensed user pair, and cognitive radio user pair communicate at the same time. For making no interference for the licensed user pair, two communication schemes are proposed. They are opportunistic communication scheme aided by the relay and concurrent communication scheme aided by the relay. In this paper, the throughputs of opportunistic communication scheme aided by the relay and concurrent communication scheme aided by the relay are given. The throughputs of opportunistic communication scheme aided by the relay and concurrent communication scheme aided by the relay are bigger than the original communication scheme without aided by relay. There is the time loss in the opportunistic communication scheme aided by the relay. The throughput under opportunistic communication scheme aided by the relay will be different with the different conditions of time loss. Hence, for the special condition, cognitive radio user pair can choose the best communication scheme from opportunistic communication scheme aided by the relay and concurrent communication scheme aided by the relay to communicate.3. Under the condition of making no interference for licensed user pair, the power allocation scheme can optimize the performance of cognitive radio user pair. Under the definition of interference temperature, unlicensed user pair and licensed user pair can share the same wireless spectrum band to communicate by using the remain rate of signal and noise on licensed user pair. In this way, making the unlicensed user pair and licensed user pair communicate in the same wireless spectrum band comes true. The system models on relay-aided Gaussian interference channel are extended combined by assumed that one pair of the user pair in system model is licensed user pair, the other pair of the user pair in system model is the cognitive radio user pair and the common relay is cognitive radio relay. The common cognitive radio relay helps the licensed user pair and cognitive radio user pair communicate at the same time. Cognitive radio user pair cooperate with cognitive radio relay to allocate the power between the cognitive radio user pair and cognitive radio relay to making no interference to the rate of licensed user pair. Allocation the power between the cognitive radio user pair and cognitive radio relay reasonable can enhance the communication rate of cognitive radio user pair, under constraint of the lowest allowed communication rate of license user pair.