Study On Spectrum Sensing And Interference Alignment Technology In Cognitive Radio

Cognitive radio (CR) is a communication technology that can intelligently sense the environment and dynamically adjust the system parameters to adapt to the changing environment. With the development of wireless communication, spectrum resource become increasingly scarce, however, this problem can be well solved by using CR technology. But secondary users (SUs) have caused serious interference to primary users (PUs) in CR spectrum sharing, interference alignment (IA) can solve this problem. IA can make the interference cast overlapping shadows at one half of the subspace of the receivers, leaving the other half with no interference for data transmission by using joint processing at the transmitters, but IA still has the problem of low signal to interference plus noise ratio (SINR) of the received signal under some channel states. Therefore, the problems of spectrum sensing in CR network and interference management in spectrum sharing have been studied in this thesis. The work accomplished specifically is as follows:(1)The energy detection based cooperative spectrum sensing algorithm and entropy based spectrum sensing algorithm in spectrum sensing are designed based on the Field Programmable Gate Array (FPGA), respectively. In the design of entropy based sensing algorithm, a new detector based on the entropy of spectrum power density is applied instead of the traditional detector based on the entropy of spectrum amplitude, which reduces the complexity of FPGA design and saves the hardware resource. From the comparison results obtained through FPGA design and Matlab simulation, it can be known that the two designed algorithms have good detection performance.(2)IA is applied in overlay CR to eliminate the interference of the network, which is different from previous literatures, the communication time criterion for the PU and SUs is built, a throughput ratio based time allocation scheme is given. Based on this, the game theory based time resource auction scheme is proposed and simulations are made for the proposed scheme. The results show that the system resource is efficiently utilized and the communication of the whole network is balanced.(3)For the problem of serious SINR decrease of IA under some channel states, the spectrum scheduling based IA optimization approach under the cases of users with fixed grouping and random grouping is given. Based on this, the spectrum scheduling based IA for underlay spectrum sharing algorithm is proposed. The objective functions in underlay spectrum sharing system are defined, the performance and computational complexity of the proposed algorithm are analyzed and simulations are made. The results show that the spectrum scheduling based IA for underlay spectrum sharing algorithm can be applied in the spectrum sharing of CR network and enhance the performance of the PUs and SUs or the PUs efficiently.