Research On Reliability Of CR-NOMA Relay Sharing Network

With the development of communication technology,the number of users and equipment of communication network increases dramatically.It is urgent to solve the problem of how to effectively use the limited spectrum resources to meet the communication needs of more users.Cognitive Radio(Cognitive Radio,CR)and NOMA(Non-Orthogonal Multiple-Access,NOMA)combination are among the solutions to the scarcity of spectrum resources.This paper mainly considers the CR-NOMA cooperative network where the primary network and the secondary network share the common relay.The secondary network borrows the spectrum resources of the primary network,and allows the primary network to communicate using the secondary network’s relay in return.The following researches are carried out:(1)When the primary and secondary networks share the same relay,the performance of the secondary network cannot be guaranteed because the primary network has a higher priority.Therefore,incremental relay is added to assistance communication when the communication quality of secondary network users is poor.The CR-NOMA system model combining the relay sharing and the incremental relay was constructed.The precise expressions of the outage probability and throughput were derived,and the theoretical results were verified by Monte Carlo simulation.In order to maximize the compromise performance of outage probability and throughput,the transmission power ratio of primary and secondary networks and the power distribution factor of the relay are optimized.The simulation results are compared with the average power distribution scheme.Through the simulation analysis of the outage performance with and without incremental relay protocol,it is concluded that adding incremental relay in relay sharing network can reduce the outage probability,increase the throughput and improve the network reliability.(2)The existence of direct links can provide additional spatial diversity and further improve system reliability.Considering the influence of direct link on the performance of CR-NOMA relay sharing network,the local users of the secondary network are used as the incremental relay of the primary network to assist transmission.Meanwhile,the remote user of the secondary network use the selective merge technique to process the signals from the transmitter and forwarded by the local users.The CR-NOMA relay sharing network model with direct link is constructed.The precise expression of system outage probability is derived.Monte Carlo simulation proves the correctness of the theoretical results.The effects of signal to noise ratio,power distribution factor,power limitation and noise variance on system outage probability are analyzed.Compared with the network where the local user does not act as the incremental relay,the proposed scheme can ensure the reliability of network.(3)In CR-NOMA relay sharing network,half-duplex relay will waste spectrum resources,while self-interference elimination should be considered when full-duplex relay is used.Two half-duplex relays are used to forward the information from the transmitter in the odd-even time slot to simulate the information transmission of full-duplex relays,respectively.The Virtual Full Duplex Cognitive Radio Non-Orthogonal Multiple Access(VFD-CR-NOMA)relay sharing network model was constructed.Considering the interference between two successive relays,the outage probability of the system is derived,and the approximate expression of the outage probability is obtained by using Gauss-Chebyshev formula.In order to improve the reliability of communication of the system,the iterative ternary search algorithm is used to determine the optimal power distribution scheme,and the optimal power distribution factor is obtained by minimizing the outage probability of the system.