Research On Cognitive Cooperative Transmission Method Based On Non-Orthogonal Multiple Access

The arrival of the fifth generation mobile communication technology(5G)brings the realization of the Internet of everything a step forward.With the wide application of wireless communication and the increasing number of devices connected to the Internet,it is important for 5G to meet the needs of users for high bandwidth,low latency,and a large number of connected services.The cognitive cooperative network allows secondary users to access the authorized spectrum of primary users opportunistically to improve the utilization rate of the spectrum,which obtains spatial gains and expands the coverage of communication by sharing resource of communication nodes.Non-Orthogonal Multiple Access(NOMA)has been identified as the key technology for 5G networks,which superimposes multiple user signals in power domain and uses the same time/code/frequency resource block for transmission.It has outstanding advantages in meeting the demand of mass connection,effectively reducing transmission delay and improving spectrum efficiency.Therefore,NOMA is applied to the cognitive cooperative transmission network to solve the contradiction between the super-large scale connection and the shortage of wireless spectrum resources,and considers the signal self-interference,channel feedback delay,phase noise and other problems in the actual NOMA cognitive cooperative network.The transmission performance of NOMA cognitive cooperative network with imperfect interference cancellation,imperfect channel state information and hardware impairment is studied and analyzed.Specific research contents and achievements are as follows:Firstly,we investigate the cognitive cooperative NOMA network with interference power constraint in underlay mode,where a primary receiver is located at the communication range of the secondary network.In the secondary network,the secondary source communicates with the cognitive near user by the direct link and with the cognitive far user through the assistance of multiple relays under cognitive radio constraint.Secondary source sends the mixed signal to the cognitive near user and to multiple relays via NOMA principle.According to the signal to interference plus noise ratio between secondary source and multiple relays,the best relay is selected to forward the decode signal to the cognitive far user.To measure the performance of the system quantitatively,the exact closed form equations for the outage probabilities of the cognitive near user and the cognitive far user are derived respectively over Rayleigh fading channels.Simulation results show that reasonable power distribution coefficient and increasing the number of relays improves the performance of cognitive cooperative NOMA network.Secondly,considering imperfect successive interference cancellation(SIC)and hardware impairment,a cooperative overlay cognitive radio non-orthogonal multiple access network is proposed to optimize cooperative diversity,which adopts the incremental NOMA cooperative transport scheme.Cognitive primary user transmitter(PT)transmits the primary user’s signals to the primary user receiver(PR)and secondary user transmitter(ST).ST acts as a relay to assist the primary network in information transmission and sends the secondary user signal to the SR.ST only sends the secondary user signal to SR when the data transmission of direct link between PT and PR is successful.ST superimposes and sends the primary user signal and the secondary user signal to PR and SR via NOMA when the data transmission of direct link is unsuccessful,and PR combines the signals received by the two hops in the cooperative transmission using the selection combining(SC).To measure the interference of imperfect SIC and hardware impairment on system performance quantitatively,we derive the end-to-end exact equation of outage probability and throughput for the primary and secondary networks.The experimental results show that imperfect SIC and hardware impairment damage reduce the outage performance of the system,but do not affect the cooperative diversity gain.Thirdly,we investigate an overlay multiple users cooperative overlay cognitive radio non-orthogonal multiple access network in the presence of imperfect SIC and imperfect channel state information(CSI).In this network,cognitive secondary sources act as relays to assist transmission from the primary user(PU)transmitter to the PU receiver via NOMA.According to the received signals between the primary transmitter and multiple cognitive secondary sources,the best secondary source with the maximum signal to noise ratio(SNR)is selected to transmit the PU’s signals and its own signal to cell-edge users through NOMA principle.Then,the PU receiver user combine the signals received from direct transmission in the first phase and relay transmission from the best cell-center cognitive SU in the second phase byelection combining.To measure the performance of the system quantitatively,we derive the end-to-end outage probability and capacity for the primary and secondary networks by taking the imperfect SIC and CSI into consideration.Finally,the performance analysis is validated by the simulations,and show that serious interference caused by imperfect SIC and(or)imperfect CSI reduce the system performance.