Capacity Analysis And Power Allocation Of NOMA In Relay D2D Communication System

Nowadays,with the continuous development of mobile communication technology,people have higher demands for the data transmission rate,network capacity,spectrum utilization rate and other aspects of the communication system.However,the bandwidth allocation under 5GHz is already very crowded,and the spectrum available for mobile communication are limited.In order to meet the needs of the development of wireless communication,Device-to-Device(D2D)communication can be used to improve the spectrum utilization and reduce the burden of communication with base stations.When the distance between two D2 D users is large or the channel condition is poor,the relay-assisted D2 D communication can improve the success rate of communication between D2 D users.At the same time,Non-orthogonal multiple access(NOMA)technology uses a single frequency band for multiple users,which effectively reduces interference between them and improves spectrum utilization.In this thesis,we present a cooperative systems that combining NOMA technology with relay assisted D2 D communications and investigate the system performance of uplink multiplexing and downlink multiplexing respectively for the scenario where cellular users and D2 D users reuse the same spectrum in a single cell cell.Furthermore,we propose an optimal power allocation strategy maximizing system capacity.The main studies are summarized as follows:1.For the scenario of downlink relaying D2 D communication,the integration of NOMA and D2 D communications effectively avoids the interference caused by the transmission power from the base station to the D2 D link..The approximate expression of system capacity under the Rayleigh channel is derived considering the case in which relay-assisted D2 D and cellular user share the downlink resources.Based on the expression,the power allocation strategy using one-dimensional search is proposed to maximize the system capacity.Simulation results verify the correctness of the theoretical derivation.The power allocation strategy has a faster convergence rate and can improve the system capacity.The simulation results also show that the system capacity using NOMA is significantly better than the system capacity without using NOMA.2.For the scenario of uplink relaying D2 D communication,D2 D transmitter can transmit simultaneously with multiple D2 D receivers by introducing the new concept of D2 D group for NOMA transmission,thus improving the spectrum utilization.The analytical expressions of theoutage probability and capacity for D2 D link are deduced considering the case in which relay-assisted D2 D and cellular user share the uplink resources.Simulation results demonstrate accuracy of the derived theoretical expressions and indicate that the system capacity is better than that case of without using NOMA.