| With the rapid development of the Internet,the Internet of Things(Io T)and the mobile communication technology,a variety of smart devices,applications and services access to the network at an unprecedented speed and scale,resulting in the exponential growth of mobile data traffic.However,the spectrum resources in wireless network are limited,how to support such a large number of connections on the limited resources and provide them with satisfactory services is an urgent problem for us to solve.In addition,devices in wireless networks,especially the Io T devices,are mostly powered by batteries with limited capacity.When the battery runs out,it is often inconvenient to charge or replace the battery for these devices.To this end,how to keep energy-constrained devices communicating sustainably and reliably,contributing to the achievement of connecting everything,is another problem to solve.Due to the merits of helping support massive connections,improving user fairness and achieving higher spectral efficiency,non-orthogonal multiple access(NOMA)is considered as a promising multiple access technology for the 5th generation(5G)mobile communication system.But NOMA alone is not enough to cope with above challenges.Therefore,in this thesis,we take NOMA as the starting point,combine it with other technologies such as full duplex(FD)communication,cooperative relaying,dynamic spectrum sharing,device-todevice(D2D)communication and wireless power transfer(WPT),and then carry out the studies for several key techniques with high spectral efficiency and high energy efficiency according to the possible application scenarios in practical systems.The main contributions of this thesis are summarized as follows:1.To resolve the contradiction between scarce spectrum resources and massive device connections along with exponentially growing data traffic,and at the same time alleviate the influence of self-interference on the performance of FD communication system,we propose a simple but spectrum-efficient NOMA-based virtual FD communication system.In this system,we replace the FD base station(BS)in existing communication systems with two half duplex(HD)and geographically separated remote antenna units,and serve the uplink and downlink users simultaneously through the centralized control of the baseband processing unit,to achieve a FD communication.To characterize the performance of the proposed system,we study the outage probabilities and ergodic rates of all users in detail.Both the theoretical analyses and the simulation results show that our proposed NOMA-based virtual FD system is superior to the existing NOMA-based FD system.2.For the scenario that the direct link between communication nodes is poor or even non-existent,we propose a NOMA-based relay-assisted spectrum sharing system.In this system,we combine NOMA,cooperative relaying and dynamic spectrum sharing technologies so that the system can not only improve the coverage of this scenario,but also significantly improve the spectral efficiency.Then,two schemes are designed for this system:multiple access broadcast cooperative NOMA scheme and time division broadcast cooperative NOMA scheme.By assuming perfect channel state information(CSI)or CSI with channel estimation error is known,for each scheme,we first perform the power optimization to minimize the outage probability of the D2 D user under the quality of service constraint for the cellular user.On this basis,we further derive the outage probabilities of both cellular signal and D2 D signal and the average throughput of the system.On the other hand,by assuming only statistical CSI is known,for each scheme,we first analyze the system outage probability and then find the optimal power allocation to minimize the outage probability.The simulation results show that our proposed schemes are superior to other benchmark schemes under three CSI cases.3.In light of the fact that bidirectional D2 D can achieve more efficient spectrum utilization than one-way D2 D,we propose a NOMA-based hybrid cellular and bidirectional D2 D cooperative communication model.In this model,two users need to receive the downlink signals from BS,meanwhile,they need to exchange information with each other.For the case that two users have abundant energy,we first derive the ergodic sum rate of the system and the outage probabilities of all signals,and then calculate their asymptotic results at high signal-to-noise ratio.While for the case that users are energy-constraint,we derive the ergodic sum rates,outage probabilities and their corresponding asymptotic results of systems under time switching(TS)and power splitting(PS)energy harvesting(EH)protocols,respectively.Simulation results verify the correctness of the theoretical analyses and indicate that our proposed schemes perform better than other benchmark schemes.4.For the massive connection scenarios in which the source nodes are energy-constraint,we propose a WPT-based cooperative NOMA(WP-CNOMA)communication system and focus on the design and optimization of this system.Specifically,in the proposed system,power beacon(PB)will be used to charge the energy-constraint information source and relay,to help the system establish the normal communication.Moreover,antenna selection and relay selection are applied to further improve the system performance.On this basis,we analyze the outage probabilities of users and the average throughput of system under both linear and nonlinear EH models,and then find the optimal EH time that maximizes the average throughput invoking the Golden section search method.In addition,by assuming full CSI is known,we jointly optimize the EH time and power allocation to maximize the minimal rate and then find the optimal solutions by exploiting a low-complexity semi-analytical method.Both the theoretical analyses and the simulation results show that our proposed WP-CNOMA system is superior to the corresponding orthogonal multiple access system. |
PDF Full Text Request