On The Peformance Analysis Of SWIPT And NOMA For Wireless Relaying Networks

With the rapid development of the current technology,mobile communication technology continues to be innovated,ranging from the first generation mobile communications system(1G)to the fourth generation mobile communications system(4G).At present,the global 4G network construction is in the ascendant,and the research of the fifth generation mobile communications system(5G)has been considered as the development direction of the future communications.Over the past years,cooperative relaying technique has been widely studied in the field of wireless communications,owing to its ability to improve the transmission reliability to increase coverage.Due to the application of micro cell and pico cell,in the future 5G network,the cell area is shrinking.Therefore,it is essential to add relay nodes in the network.As relay nodes may have limited capacity batteries in practical communication systems,recharging or replacing batteries of relay nodes may be inconvenient or can incur a high cost in some scenarios.Thus,how to prolong the service life of the communication system has become a research hotspot.Furthermore,to deal with the problem of energy shortage,it has also been a hot issue in the communication industry that how to reduce energy consumption.Consequently,simultaneous wireless information and power transfer(SWIPT)emerges as a new technology of energy collection,which allows the energy constrained node harvest energy and process the information at the same time,so as to prolong the lifetime of wireless network and improve the energy efficiency.On the other hand,for the new demand of spectrum efficiency and system capacity in the further network,traditional orthogonal multiple access(OMA)has no longer satisfied.Hence,a new technique,i.e.,non-orthogonal multiple access(NOMA),has attracted more and more attention.At the transmitter,NOMA superposes the signals of multiple users at the same time-domain,frequency-domain,and code-domain,but in different power-domain.At the receiver,the successive interference cancellation(SIC)technology is carried out to separate and detect the signals of multiple users.Considering the above reasons,in this paper,we focus on the study of SWIPT and NOMA technologies in 5G,and combine them with relaying networks to improve energy efficiency and spectral efficiency.The paper makes some deep analyses and optimization of the system performance for different system models,fading models,and channel conditions,and the main works and contributions are summarized as follows:1.Apply SWIPT into two-way amplify-and-forward(AF)relaying system,where all n-odes are equipped with single antenna and the energy-constrained relay nodes do not have energy themselves.Following the power splitting-based relaying(PSR)protocol,the received signal at the relay node during the first time slot is split into two proportion,one for energy harvesting and the remaining portion for information processing.During the second time slot,the relay node amplifies the remaining signal strength and then broadcasts the signal to two source nodes using the harvested energy.Since the power splitting ratio(PSR)depicting the trade-off between the harvested energy in the first time slot and the forward signal's power in the second time-slot,it is crucial to choose a reasonable value for the PSR in practical system design.Therefore,an optimal power allocation(OPA)scheme is proposed in the paper,where the optimization of PSR and the transmission power at two source nodes are jointly taken into account to minimise the outage probability,and the closed-form solutions for the OPA scheme is derived.Furthermore,a joint OPA and relay selection schemes are presented to further improve the system performance.By comparing the OPA scheme with another three sub-optimal schemes via computer simulations,the superiority of the OPA scheme is demonstrated.2.Apply SWIPT into multiple-antenna multiple-relay decode-and-forward(DF)relaying system,and a joint relay-and-antenna selection(JRAS)scheme is presented.Using the JRAS scheme,the best transmit antenna at the source node,the best relay node,and the best transmit antenna at the selected relay node are jointly determined.The outage performance of the system is analyzed and exact closed-form expressions for the outage probability are obtained.Simulation results verify the correctness of the theoretical analysis and the advantage of the JRAS scheme.3.Apply NOMA into signal-antenna one-way relaying system,where the base station communicates with multiple users simultaneously via an AF relay node.The outage performance of the considered system is deeply studied and closed-form expressions and lower bounds for the outage probability are obtained over Nakagami-m fading.By approximating the lower bounds in the high signal-to-noise ratio(SNR)regime,the diversity gains of the network can be attained.Besides,the ergodic sum rate achieved by all mobile users in the network is investigated,and expressions for the upper bounds of the ergodic sum rate are derived.Simulation results show that NOMA can provide higher system throughput and user fairness.4.Combine NOMA with multiple-antenna AF relaying networks,where the base station and the mobile users are equipped with multiple antennas while the relay node is equipped with a signal antenna.During the first time slot,a best antenna is selected at the base station to transmit signal to the relay node,where the transmit antenna which maximizes the instantaneous SNR at the relay node is chosen.During the second time slot,the users process the received signals by adopting maximal ratio combining(MRC).The expressions for the outage probability over Rayleigh fading is obtained,and the lower bounds for the outage probability and diversity order are attained as well.Simulation examples are given to show the correctness of the theoretical analysis and the superiority of NOMA.5.Consider a NOMA signal-antenna AF relaying system,where the direct links between the base station and users are available and there exists errors during the channel estimation.The exact expressions and lower bounds for the outage probability and the diversity order of the network are derived over Nakagami-m fading.Moreover,the ergodic sum rate for the proposed network is analyzed and the closed-form expressions for the upper bound of the ergodic sum rate are attained.Finally,extensive numerical results are presented to confirm the correctness of our analysis.In addition,when the SNR is very high,the outage probability maintains a non-zero constant due to the presence of channel estimation errors.This non-zero constant is termed as error floor(EF)and can not be completely eliminated.