Non-Orthogonal Multiple Access Technology Based On Massive Machine Type Communication

Recently,with the rapid development of the smart economy and the explosive growth in demand for smart terminal devices,the vision of interconnection of all things has brought great challenges to wireless communication technology.Aiming at the problem of short packet communication in large connections.The 5th Generation of Mobile Communication(5G)proposes an application scenario of Massive Machine Type Conmunication(mMTC).mMTC is mainly used in terminal networks with large connections,short data,and sparse services.In the mMTC network,the service sparse feature requires that the terminal initiates a random access procedure to the base station before performing uplink data transmission.The simultaneous access of a large number of users will lead to a more serious problem of preamble resource conflict in the random access process,and the performance of random access will drop sharply.Therefore,the increasing trend of large user connections puts forward higher requirements for random access technology.Traditional Orthogonal Multiple Access(OMA)cannot meet the needs of large-scale intelligent terminal communication in the future.Compared with OMA,non orthogonal multiple access(NOMA)technology can not only greatly improve the system capacity,but also greatly increase the user transmission rate.The randomness of short packet service in mMTC network requires that users need to establish a connection with the base station through the random access process before transmitting uplink data.Random access mainly affects the number of users in mMTC networks.The NonOrthogonal Multiple Access(NOMA)system is combined with random access to research the issues of power control and system throughput.Therefore,from the perspectives of large connections and sparse characteristics of shortpacket services,NOMA technology is combined with random access system to study the problem of spectral efficiency and access users in the mMTC network.First of all,the problem of spectral efficiency in uplink NOMA random access system is investigated.Without user quality of service(Qo S)constraints,the problem evolves into a standard convex optimization problem.A power control algorithm based on iterative waterfilling is proposed.In the case of user Qo S constraints,the closed-form solution of optimal power control within the group is obtained by using Lagrangian equation and KKT conditions.A suboptimal power control algorithm based on continuous convex approxi-mation is proposed.Finally,the simulation results show that the system performance of the NOMA power control algorithm is significantly better than that of the OMA algorithm.Subsequently,considering the large connection characteristics of mMTC,the throughput of multi-user competitive NOMA random access system is studied.Based on successive interference cancellation(SIC)technology,the concept of preset power level is proposed.The expression of throughput lower bound for multi-user competitive NOMA random access system is derived.The problem of interference between users is researched,and the exact expression of system throughput is deduced.Finally,the results of simulation show that the throughput of the NOMA scheme is better than that of the traditional OMA random access system.Finally,the throughput of non-equi-probability competitive NOMA random access system is researched.The concept of power adjustment factor on the model assumptions of SIC is proposed.On this basis,the probability of users choosing different power levels is investigated.The mathematical model of system throughput is established and the optimization problem is transformed into a nonlinear programming problem.Compared with the traditional OMA random access scheme and the equal probability NOMA random access scheme,the numerical simulations show that the performance of the optimized scheme is proved to be better.