Tansmission Optimization In Cognitive Radio Networks

With the improvement of modern technology,wireless communication technology has been developed rapidly in recent years and it requires sufficient spectrum resources.Most of spectrum resources have been divided to the primary users,but it is not significant for the frequency division multiplexing and code division multiplexing technology to improve the efficiency of spectrum utilization.Therefore,the cognitive radio technology is introduced.In a cognitive radio network,the secondary users are allowed to utilize the frequency bands of primary users when these bands are free at present.To support this function of spectrum reuse,the secondary users are supposed to sense the radio frequency.Probability of detection and probability of false alarm are two parameters associated with spectrum sensing.Firstly,from the perspective of primary users and the secondary users,we set the approprnate weights for each user and prove the existence of the optimal perception time by the energy detection scheme.The throughput optimization model is established and find the optimal sensing time which can obtain the maximum network throughput.Then,in order to save energy and improve spectral efficiency at the same time,the trade-off optimization between energy efficiency and spectral efficiency is analyzed,and the optimization scheme of power allocation algorithm is proposed.The simulation results of MATLAB show that the proposed algorithm is more superior.The specific contents are as follows:(1)A cooperative sensing scheme based on total error probability is proposed to judge the detection performance of secondary users.Firstly,the secondary users who are about to participate in cooperative perception need to be collected according to the total error probability.Secondly,the weight coefficients which will be allocated to each secondary user are optimized.Thirdly,the throughput of cognitive network is analyzed and this thesis proves the existence of the optimal sensing time.Fourthly,the experiment testifies the proposed cooperative sensing scheme can achieve higher radio network throughput.(2)In large-scale MIMO systems,a power allocation algorithm which can optimize energy efficiency and spectral efficiency jointly is proposed.Firstly,the downlink system model of MIMO system is established and analyzed from channel estimation and downlink transmission rate.Secondly,the joint trade-off between energy efficiency and spectral efficiency and the principle of power allocation algorithm are described.Thirdly,the power allocation optimization algorithm which proposed in this thesis is analyzed.Fourthly,the simulation results manifest that the proposed power allocation algorithm can optimize the energy efficiency and spectral efficiency on the basis of the traditional algorithm.