Optimization Design And Performance Analysis For Cooperative NOMA Systems

In recent years,due to the rapid development of wireless communication technology,the number of Internet of Things access devices has increased significantly,and the spectrum resources are increasingly scarce.Non-Orthogonal Multiple Access technology allows multiple users to share spectrum resources,achieving higher spectrum utilization,greater device access and lower transmission latency.Cooperative communication technology improves system transmission reliability through user collaboration.In practical applications,cooperative relay devices are usually powered by batteries,and the frequent replacement of batteries will increase costs.Wireless Information and Power Transfer technology enables Internet of Things devices to collect energy from radio frequency signals,achieve simultaneous transmission of information and energy,and greatly alleviate the pressure on energy constrained devices.In order to achieve higher spectral efficiency and energy efficiency in wireless networks,cooperative relay and SWIPT technologies are applied to NOMA communication systems to optimize the design and performance analysis of cooperative NOMA systems,the main research contents are as follows:(1)For a single relay multi user cooperative NOMA system,considering the situation where there is a direct link between the base station and the user,users are ranked and paired based on channel gain,and a theoretical expression for the outage probability of the paired users is derived,and the asymptotic expression for the outage probability under high signal-to-noise ratio conditions is analyzed to obtain the diversity order.The correctness of theoretical derivation is verified through simulation experiments and the optimal power allocation coefficient is analyzed.Simulation results show that adding direct links can improve user outage performance.The impact of direct links on system outage performance is greater than that of relay links.The user’s outage probability is related to the location of the relay.When the location of the relay is around 60% of the distance between the base station and the user,the outage performance reaches the best.Different user pairing schemes can lead to different outage performance,choosing users with good channel conditions for pairing results in a lower outage probability.(2)For the cooperative NOMA communication system based on SWIPT,the system power allocation problem is optimized and designed on the premise of meeting the Quality of Service of remote users.A power allocation scheme based on Genetic Algorithm-Particle Swarm Optimization algorithm is proposed.The optimization model and objective function are established to maximize the sum rate of the system,and the optimal power allocation coefficient and optimal power division factor are solved.The simulation results show that the proposed algorithm effectively reduces computational complexity,improves the sum rate by 32.92%and 11.13% respectively,and improves energy efficiency by 70.12% and 6.64%respectively compared to fixed power division factor algorithm and monotone optimization algorithm.