| With the evolution of 5G technology,the process of the Internet of everything has been greatly improved.However,with the continuous growth of devices connected to wireless network,the scale of the wireless network has increased sharply,and people's demand for low delay and high speed of wireless network has become increasingly strict.Therefore,how to provide high quality communication service while users access wireless network has been widely studied and discussed.Cognitive radio-non-orthogonal Multiple Access(CR-NOMA)systems are considered to be effective technologies that can solve people's demands for large-scale connection,high speed and high reliability of mobile communication in 5G era.Therefore,in order to improve the sum rate of secondary users(SUs),the power allocation algorithm of CR-NOMA system with multiple users,imperfect successive interference cancellation as well as imperfect successive interference cancellation and imperfect channel state information are studied respectively.The main innovations and contributions of our works are as follows:1.A power allocation algorithm based on tabu search and Q-learning is proposed to improve the sum rate of SUs in CR-NOMA system with multiple users by optimizing power allocation.In the system,multiple SUs are connected to the channel of primary users(PUs)by superposition coding technology,cognitive base station(CBS)learns the optimal power allocation scheme while allocating power to users The executive power allocation action,channel state of system and sum rate of the SUs in original optimization problem were expressed as the actions,states and rewards in the Markov decision process respectively.Tabu search and Q learning were used to solve the problem,and then a tabu Q table about actions,rewards and tabu objects was obtained.In consideration of the constraints of quality of service of PUs,the normal communication of SUs and the maximum available power of system,CBS obtains and executes the optimal power allocation scheme by searching the tabu Q table,then improves sum rate of SUs by optimizing power allocated to them.Simulation experiments show that the proposed power allocation algorithm has obvious advantages over other power allocation algorithms compared in terms of sum rate and the number of SUs in CR-NOMA system.2.Considering the residual interference caused by imperfect successive interference cancellation,the problem of maximizing sum rate of SUs in CR-NOMA system by optimizing power allocation was studied.In order to solve the problem,a power allocation algorithm based on parameter transformation and KKT(Karush-Kuhn-Tucker)condition was proposed.In the system,without affecting the quality of service of PU,the signals of multiple SUs are transmitted by superposition coding.Considering limitations such as the maximum available power of system,firstly,the constraints in original optimization problem are transformed and a new problem is constructed.Further,the new problem is solved through KKT conditions and the optimal power allocation factor of SUs is derived.Finally,the goal of maximizing sum rate of SUs is achieved.Compared with other power allocation algorithms by simulation experiments,the result show that proposed algorithm has obvious advantages in both sum rate of SUs and anti-interference ability to eliminate the residual interference generated by imperfect successive interference cancellation.3.In CR-NOMA system,the channel estimation error interference caused by imperfect channel state information and the residual interference caused by imperfect continuous interference elimination condition are considered simultaneously.The problem of optimal power allocation for SUs to maximize sum rate of them is analyzed and discussed,then a stepwise power allocation algorithm is proposed to solve the optimization problem.Considering the constraints of quality of service of PU and SUs as well as the maximum transmitting power of system,first step is to fix the value of total power of SUs through the method of parameter fixing and obtain the closed form solution of optimal power allocation factors.The second step is to substitute the obtained optimal power allocation factors into original optimization problem to construct a new problem and solve the fixed total power value at the beginning by using successive convex approximation method,finally achieve the goal of improving sum rate of SUs in system.The simulation experiments show that compared with other algorithms,the proposed algorithm performs better on sum rate of SUs in CR-NOMA system,and has obvious advantages in anti-interference ability under imperfect successive interference cancellation and imperfect channel state information. |
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