Research On Relay Transmission Scheme Based On Non-Orthogonal Multiple Access

NOMA technology has the advantages of high spectrum efficiency,high amount of equipment access.It is helpful to build a wireless communication network with higher capacity,and lower delay.It is considered to be one of the key technologies for improving wireless communication system performance.Cooperative communication technology has the characteristics of anti-multipath effect,effectively expanding the coverage area of communication,and improving system diversity gain.Its emergence has caused changes in the field of mobile communication.Compared with half-duplex technology,full-duplex technology can effectively increase system capacity and has broad prospects of application.However,when NOMA technology is combined with full-duplex cooperative communication technology,there will be signal interference problems,and the analysis of system performance is more complex.Therefore,the research on the system's outage performance and ergodic capacity has guiding significance for the study about full-duplex cooperative communication based on NOMA.This thesis mainly studies the NOMA fullduplex cooperative communication system's outage performance and ergodic capacity based on single-user and multi-user at the cell edge,and proposes an improved system transmission scheme for different system models and studies the power allocation problem.This thesis first proposes an improved transmission scheme about cell edge single-user fullduplex cooperative communication system based on NOMA.Different from the existing research,the signal from the cooperative link is regarded as useful signal thus the signals from the direct link and the cooperative link are received and processed by the way of maximum ratio combining.The transmission scheme can effectively improve the overall ergodic rate of the whole users in cell and the system.Under the premise of deducing the outage probability and ergodic rate of each user in the system based on this transmission scheme,according to the situation of unknown and known instantaneous channel state information on the transmitter,the power allocation problem of the system is studied for the purposes of minimizing the outage probability and maximizing the minimum achieveable user rate.The simulation proves that compared with the existing research scheme,the proposed transmission scheme can further improve the system ergodic capacity while ensuring system reliability.Considering the fact that the number of cell-center users and cell-edge users are often not equal and the problem of not being able to fully utilize the full bandwidth after cell-edge users and cell-center users are paired,this thesis adopts a system transmission scheme named time slot split-bandwidth sharing.The scheme effectively improves the system ergodic capacity under the premise of ensuring that the paired users occupy the full bandwidth.In addition,this thesis also applied a new signal transmission scheme at relay node to NOMA full-duplex cooperative communication system.Different from the existing scheme of the relay node forwarding a single signal,this scheme allows the relay node to decode the users' signal first and then re-encodes the signal according to the new power allocation factor and last forwards the new NOMA mixed signal.The thesis deduces the single-integral and closed form solutions for the outage probability and the ergodic rate of each user and the system based on this transmission scheme and studies power allocation problem about the system according to the principle of maximizing the minimum achieveable rate of the system.Finally,the thesis verifies the influence of power allocation factor,distance between base station and relay node and users' target rate on performance of the system based on the transmission scheme by simulation results.Simulation results show that this transmission scheme can further improve system ergodic capacity.