Research On New Multiple Access Technology In Relay Systems

The relay technology has been rated as one of the key technologies of 5G (5th Generation) because it can significantly improve the capacity and coverage of mobile communication system. The relay technology can transform the direct link into multi-hop links and bring channel diversity gain to the mobile communication system. However, with the development of mobile internet and internet of things, the 5G communication system in the future will face the challenges of ultra-high traffic density, ultra-high connection density and high mobility. The relay communication system using OMA (Orthogonal Multiple Access) is not able to meet the requirements of the new generation communication system. NMA (Non-orthogonal multiple access), as a new multiple access technology, has become an important trend of the development of communication networks in the future. Among them, the SCMA (Sparse Code Multiple Access) can achieve overload of communication system with sparse codebooks. With the advantages of low complexity of the receiver and no-authorization access, SCMA has been considered as one of the most promising candidates of the 5G multiple access technology.Therefore, integrating the no-orthogonal multiple access technology into the relay system will be of great practical significance and development prospects.With requirements of the 5G communication system in the future to improve the utilization of wireless resources, this thesis studies the new multiple access technology in relay system with the support of vertical and horizontal laboratory projects. Among them, the main research focuses on the joint resource allocation of SCMA uplink multi-user single relay assisted system and SCMA uplink multi-user multi-relay assisted system.Firstly, in this thesis, the no-orthogonal access technology and relay technology are systematically studied and elaborated. Because the concept of multiple access technology is quite broad, this thesis mainly introduces four kinds of typical NMA technologies, which are MUSA(Multi-User Shared Access), PDMA (Pattern Division Multiple Access),NOMA (Non-Orthogonal Multiple Access) and SCMA. Based on the research of relay technology, this thesis mainly focuses on the combinations of relay technology with other new technologies and analyzes the characteristics of resource allocation in relay system.In this thesis, as for the study of the SCMA uplink multi-user single relay system, a transmission strategy with the combination of the SCMA and OFDMA (Orthogonal Frequency Division Multiple Access) is proposed at first. Then, under the condition that the power of user equipment and relay transmit are limited, the problem of joint resource allocation of codebook allocation, power allocation and subcarrier pairing is solved to optimize the system weighted sum-rate. Since the optimization problem is a mixed integer problem, the original problem is split into two independent sub-problems of joint resource assignment of codebook with power and subcarrier pairing. By solving these two sub-problems iteratively, the IJRASP (Iterative Joint Resource Allocation with Subcarrier Pairing Algorithm) is proposed. Simulation results show that IJRASP can enhance the weighted sum-rate and energy efficiency of the system to realize efficient communication in different dimensions compared with that in the OFDMA multi-user single relay assisted system.Based on the research of SCMA uplink multi-user single relay assisted system, considering that usually there are multiple available relays around each user equipment, we study the SCMA uplink multi-user multi-relay assisted system. In the SCMA uplink multi-user multi-relay assisted system, a two-phase transmission strategy consist of multi-user broadcasting information and single relay forwarding information is proposed. Based on the optimization objective of weighted sum-rate of the system, this thesis proposed a new joint resource allocation algorithm named JRARS (Iterative Joint Resource Allocation with Relay Selection Algorithm), which jointly considers relay selection, codebook allocation,power allocation and subcarrier pairing. The algorithm is divided into two steps: In the first step, under each possible relay selection scheme, a joint resource allocation of codebook allocation, power allocation and subcarrier allocation based on the optimization of weighted sum-rate of the system is implemented; In the second step, the optimal relay is selected through the one-dimension search method. Simulation results show that JRARS can improve the system performance of both the weighted sum-rate and energy efficiency, thus realize efficient communication in SCMA uplink multi-user multi-relay assisted system.Finally, this thesis analyzes the tradeoffs between the upper limit of transmit power of user equipment, the number of OFDMA subcarriers and the number of relays and the system weighted sum-rate, energy efficiency, receiver complexity in the SCMA uplink multi-user multi-relay assisted system. For couple of practical application scenarios,this thesis also gives some useful recommendations.