The Research On Outage Probability And System Throughput Of Cognitive NOMA With SWIPT

Non-orthogonal multiple access(NOMA)is considered as a promising multiple access technology in the future mobile communication because of its high spectral efficiency.Cognitive radio(CR)has become a new model to make efficient use of scarce spectrum resources.If NOMA and CR can be combined organically,higher spectral efficiency can be obtained.In addition to improving the spectrum efficiency of wireless networks,another key goal of 5G is to improve energy efficiency.Consider the combination of wireless energy transfer and information transfer,called Simultaneous wireless information and power transfer(SWIPT),in which the signal for information transfer is also used for energy extraction.Therefore,SWIPT is applied to the cognitive-based NOMA model to further improve the energy efficiency of the system.Firstly,a collaborative transmission scheme based on the overlay NOMA model is proposed,that is,by using NOMA technology,the secondary transmitter(ST)acts as a relay,helping to transmit both primary and secondary network information.According to the statistic characteristics of Nakagami-m fading channels,the outage probability and throughput for the primary and secondary networks are respectively derived in closed forms.The simulation results show that the performance is improved by NOMA-based cooperative transmission scheme.It also reveals that NOMA is superior to traditional orthogonal multiple access(OMA)and achieves better spectrum utilization.Secondly,a new cognitive NOMA model based on SWIPT is proposed,that is,ST acts as a EH relay,decoding and collecting energy at the same time.In the proposed model,ST acts as a decodeand-forward relay to help forward primary information and collects energy from it by using SWIPT.The outage probability and throughput for the primary and secondary networks in the transmission scheme are also deduced.The simulation results show that the outage probability of the system is reduced and the throughput is improved by adopting the cognitive NOMA transmission scheme based on SWIPT.This phenomenon reveals that the energy cooperative cognitive NOMA system can improve network performance.Thirdly,it is improved based on the above scheme.There is no direct circuit between the primary and the secondary network,which needs to be forwarded through relay,so an improved collaborative transmission scheme based on NOMA model of overlay CRNs is proposed,in which PT and ST share the same relay.The analytic expressions for outage probability and system throughput are written in closed form.The simulation results show that,in the case of poor channel conditions of direct connection between the primary and secondary networks,the system outage probability is reduced and the system throughput is improved by using the improved transmission scheme.