Research On Anti-interference Spectrum Access Method In Cognitive Cooperative MIMO Systems

With the rapid increase of wireless network at an unprecedented speed,wireless communication gradually plays an increasingly important role in people's daily life.The conflict between the limited spectrum resources and the ever-increasing demand for wireless communications is exacerbated.How to improve the efficiency of spectrum utilization is a major issue faced by researchers all over the world engaged in the research of wireless communications.Cognitive radio as a new technology that has ability to effectively improve the utilization of spectrum resources has attracted close attention of researchers at home and abroad.Since MIMO wireless technology is able to significantly increase the capacity of a given channel by increasing the number of receiving antenna and transmit antennas without increasing the system bandwidth and the total transmitting power of the antenna,it has also become one of the most important wireless technologies in recent years.Among the existing coexistence spectrum access methods,there is usually interference between primary user and secondary users,and resources are allocated by setting interference threshold.However,in the background of cognitive MIMO system,this paper uses zero force beamforming(ZFBF)and Orthogonal Frequency Division Multiplexing(OFDM)to solve the problem of interference between primary users and secondary users,researches on the anti-jamming cooperative spectrum access method with higher spectral efficiency,and analyzes the resource allocation problem.The main work and achievements are as follows:(1)For the interference problem between primary user and secondary users in cognitive MIMO network,this paper first proposes a ZFBF-based anti-interference spectrum access method in cognitive MIMO network.In this method,the secondary users use the ZFBF to design beamforming factor in the second phase to eliminate the co-channel interference between the primary users and the secondary users.Then the power allocation is optimized maximize the transmission rate of secondary users while ensuring that the primary users reach the target rate.Simulation results show that this method can improve the communication performance of both primary users and secondary users.In order to further improve the spectrum utilization rate,an anti-jamming spectrum access method optimized by combining time slot with power is proposed.Namely after the beamforming factor is designed by ZFBF,the slot length and power allocation are jointly optimized to maximize the secondary users transmission rate under the condition of the primary user reaching target rate.Simulation results show that the proposed method has better transmission performance than fixed-slot length transmission.(2)For frequency-selective fading channel,an anti-interference spectrum access method based on OFDM in cognitive MIMO network is proposed.In this method,the secondary users use a part of subcarriers to transmit the primary user's information in the second time slot,and then use the remaining sub-carriers to send its own information to eliminate the interference between the primary users and the secondary users.This method maximizes the transmission rate of the secondary system through the optimal subcarrier allocation and the optimal allocation of power on the subcarriers while ensuring that the primary system reaches the target rate.Simulation results show that this method not only guarantees the communication performance of primary users,but also has good gains in cognitive system.