Research On Downlink Key Technologies Of Non-orthogonal Multiple Access Systems

In order to better meet the development of mobile Internet and the popularity of smart terminals,5G mobile communications have emerged at the historic moment.Non-orthogonal multiple access technology has received widespread attention as one of the 5G candidate technologies.Meanwhile,the advent of the 5G era has put forward higher requirements for data transmission rates and signal coverage.As a highly efficient wireless transmission technology,the cooperations between relay technology and NOMA are on the horizon.This article takes NOMA and cooperative communication as the research object,and studies the key technologies such as user grouping and power allocation of downlink NOMA system from the direction of multi-carrier multi-user downlink NOMA resource allocation and optimal sum-rate in cooperative communication.For multi-carrier and multi-user downlink NOMA resource allocation,the role of time-frequency resource units in the NOMA system is more detailed.The concept of time division is introduced to study system throughput on the basis of a combination of user grouping methods,power allocation schemes,and interference cancellation technologies.In order to improve the throughput of the system,a linear water injection algorithm is used between subcarriers,and a fractional transmit power allocation algorithm is used among different users on the same subcarrier.And,unlike the assumption that the number of near and far users is equal in the existing references,this article considers more practical scenarios where the number of near and far users is different.At this time,in order to be able to schedule more users,the concept of time division is adopted on each subcarrier,that is,the entire time period t is divided into two time slots,and dynamic grouping of different users is realized in different time slots.On the basis of fairness,the sub-channel resources are fully utilized to optimize the system throughput.For the research of sum-rate optimization in cooperative communication,considering the coverage of base stations,a relay system is introduced to ensure the accuracy of signal transmission.In reality,users at the edge of the coverage area often cannot establish a stable direct link with the base station.To this end,a relay system is introduced to assist signal forwarding.It is assumed that the base station simultaneously serves one user j in a user group M that is slightly closer to the base station and a scarce user i located at the edge of the base station.To simplify the problem,ignore the direct communication link between the source node and the user.Taking the maximal sum-rate of the NOMA system under cooperative communication as the objective function,the lemma is used to transform the maximization of the sum-rate into the reciprocal of the signal-to-noise ratio.Combined with the actual constraints,the KKT condition is used to construct the Lagrange equation for finding the optimal solution.