Investigation Of Non-orthogonal Multiple Access And Related Techniques For The Cooperative Relaying Systems

Since Claude Shannon concluded in his paper,“A mathematical theory ofcommunication”,that the AWGN channel capacity can be achieved if and only if the input signal follows Gaussian distribution and there is no way togain more capacity except by either enlarging the system bandwidth or raising the received signal-to-noise ratio(SNR)in 1948,seeking communications with higer data rateis the motive force for both academia and industry.However,for the radio access network(RAN),the design of a suitable multiple access technique is one of the most important aspects in improving its system capacity.Multiple access techniques can broadly be divided into two categories,namely,orthogonal multiple access(OMA)and non-orthogonal multiple access(NOMA).The NOMA breaks the limit of the existing OMA techniques,and exhibits huge inherent potential in theaspects of capacity,connection,and latency.Besides,NOMA shows good compatibility with other existing physical layer techniques,such as millimeter wave(mm Wave)and massive multiple-input multiple-output(MIMO),to further improve system capacity.In this dissertation,we investigate non-orthogonal multiple access and related techniques for the cooperative relaying systems,and the contributions are summarized as follows.1.We investigate the architecture of NOMA-based cooperative relaying network.We begin with an introduction of the existing relay-assisted NOMA systems by classifying them into three categories: uplink,downlink,and composite architectures.Then,we discuss their principles and key features,and provide a comprehensive comparison from the perspective of spectral efficiency,system asymmetry,and power allocation schemes.A novel strategy termed hybrid power allocation is further discussed for the composite architecture,which can reduce the computational complexity and signaling overhead.2.A novel scheme termed as NOMA operation unit with parallel SIC,which improves the fairness of cell-edge user,is proposed,and such a unit is composed of N cell-centre users and a cell-edge user.Based on a 2 cell-centre users configuration,a closed-form solution is derived for the ergodiccapacity of the proposed NOMA operation unit,and users' fairness index is also provided.Simulation results show that the proposed NOMA operation scheme not only achieves higher spectral efficiency but also shows a better fairness performance when compared with the existing NOMA operation scheme and the conventional OMA scheme.3.We study the performances of two kinds of NOMA-based cooperative relaying network:the downlink and composite architectures.We first study the performance of a downlink NOMA cooperative relay system with a single relay over Nakagami-m fading channels,where the statistical channel state information is available and both decode-and-forward(DF)and amplifyandforward(AF)protocols are considered.For DF relaying,both ergodic sum rate and outage probability are solved in closed form.For AF relaying,closed-form asymptotic ergodic sum rate and outage probability are provided.Furthermore,to make good use of the messages from the strong users to further exploit the advantages of NOMA,a diversity enhancing scheme is proposed for the downlink cooperative NOMA systems.And then,the composite architecture is investigated,where two decode-and-forward relays assist the communication between asource and a destination and the direct link between them isnot available.We analyze the system performance under the assumption that either the statistical channel state information(S-CSI)or instantaneous channel state information(I-CSI)is known to the network.For the S-CSI assumption,the achievable sum-rate at high signal-to-noise ratio is first solved in closed form,and the corresponding fixed power allocation schemes,includingthe theoretically optimal and practical suboptimal ones,are thenproposed.For the I-CSI assumption,the achievable sum-rateis analyzed and the optimal dynamic power allocation schemeis also proposed.