Research On Algorithms Of D2D Communication Mode Selection For Users With Multiple Priorities

With the rapid development of wireless technologies and the increasing popularization of intelligent terminals,the users' demand for quality of service is increasing.The performance of wireless access technologies is moving towards greater density,higher speed and lower latency.Meanwhile,the problems such as lack of wireless spectrum resources,difficulties in accessing communication equipment and low communication rate are also increasing.As one of the key technologies of 5G,Device-to-Device(D2D)communication refers to a technology in which devices within a certain distance directly communicate without a base station.The technology has the characteristics of improving spectrum efficiency,reducing the load of the base station,increasing the user data rate,reducing the energy consumption and reducing the end-to-end delay.Hence,it has attracted extensive attention from the academia and industry.The thesis mainly studies the mode selection and resource allocation algorithm of D2 D communication.Firstly,a cell is divided into multiple geographical grids with equal size,with position information of each grid available,an offline channel state information(CSI)retrieval model is introduced,which will be used to estimate the SINR and data rate of the links.Then based on this model,with constraint on minimum data rate of each link,an optimization problem is formulated to maximize the sum rate of all users to make the decision of mode selection and resource allocation.Then a differential evolution algorithm is employed to solve this problem to find the optimal mode and resource allocation.Firstly,the solution vector of this optimization problem is encoded to reduce the vector dimension,and then the penalty function method is used to deal with the constraint conditions.The constrained optimization function is transformed into the corresponding unconstrained fitness function.Finally the suitable mutation operator is allocated to find the optimal solution.Taking into account the users with multiple priorities in the system,the thesis also considers user priority and fairness factor when making the decision of mode selection and resource allocation.Firstly,the priority factor is used to control the user's transmit power,and a logarithmic utility function is used to control fairness between users.In addition,based on the mode selection and resource allocation decision,a Jain index is introduced to evaluate user's satisfaction.The simulation results show that considering the actual situation,the mode selection and resource allocation algorithm based on the offline channel model proposed in this thesis outperform the one with traditional path loss model in terms of increasing the system sum rate.Furthermore,considering the user priority and fairness,the algorithm proposed in this thesis can achieve higher user's satisfaction.