Research On NOMA-based 5G D2D Relay Selection And Power Allocation Algorithm

In the 5G(5th Generation Mobile Communication)network,how to improve spectrum utilization is an urgent problem to be solved.Since 5G candidate technologies such as Massive Multiple-Input Multiple-Output(M-MIMO),millimeter-wave,non-orthogonal multiple access(NOMA),and device-to-device(D2D)technologies can increase spectrum efficiency without cost high,which has attracted people's attention.Therefore,the combination of NOMA and D2 D gives full play to the advantages of the two hot technologies and is very suitable for 5G scenarios.It is of great significance to carry out related research.This paper focuses on relay selection and power allocation algorithms in D2 D cooperative communication based on NOMA.In the NOMA-based D2 D cooperative communication process,the base station adopts the NOMA method to implement signal transmission with two users at the near-end and the far-end.The base station communicates with the near-end device through a direct connection while communicating with the remote device through a cooperative relay.Relay and remote users use D2 D connection,so the choice of relay has a great impact on system performance.This paper first analyzes the relationship between the relay location and the average throughput of the relay link,defines the concept of the best distance,and proposes a relay selection algorithm based on the best distance.The simulation results show that outage probability of the system uses this algorithm is lower than that of the random relay selection system.However,the relay selection based on the optimal distance cannot guarantee the maximum rate of the relay link.Therefore,the paper discusses the relay selection algorithm based on the maximum relay link rate,and carries out a simulation analysis of the algorithm.The simulation results show that this algorithm can achieve higher system throughput than using the best distance-based relay selection algorithm.Although the above two algorithms all improve the system performance to a certain extent,the above two relay selection algorithms do not consider the actual capabilities of the equipment.Therefore,this paper proposes a utility value-based approach that combines the remaining energy and mobility of the equipment.The simulation results show that the relay selection algorithm based on utility value is more appropriate than the above two relay selection algorithms in the actual scenario.In the above analysis of the relay selection algorithm,the base station uses a fixed power allocation factor to achieve communication with the near-end user and the far-end user,that is,during the relay forwarding phase,when the base station communicates with thenear-end user,the transmit power does not change.That is,the base station will not increase the transmission power to the near-end user because the base station does not send a signal to the remote user during the relaying phase.This may lead to situations where the power of BS is not fully utilized.Therefore,this paper proposes an improved scheme to improve power utilization and improve system throughput by changing the power allocation factor when the base station communicates with the near-end user in the relay forwarding phase.The simulation results show that using the improved scheme can effectively improve the system throughput.Thus proved the feasibility of the scheme.