| The fifth-generation (5G) mobile communications system will emerge to meet new and unprecedented demands, which include explosive growth of data traffic, massive increase in the number of devices and continuous emergence of new services and application scenarios. Device-to-device (D2D) communication, as a key technology of5G, has the potential to offload the burden of base stations (BSs), reduce the transmission power, lower the transmission delay and improve the spectrum efficiency. D2D technology is especially advantageous for some local services, compared with other similar technologies.In the hybrid cellular and D2D network, since D2D users may share resources with cellular users, the inter-system interference is unavoidable. Therefore, it is necessary to investigate the radio resource management (RRM) of D2D communications. This thesis investigates the RRM of D2D communication from three aspects, i.e. energy efficiency (EE), peak data rate and new application scenarios. The major contributions of the thesis are described as follows.Firstly, a resource allocation algorithm that can maximize the energy efficiency of the D2D system is proposed. We analyze the EE of a single D2D link in both non-cooperative mode (NCM) and cooperative mode (CM), and prove that the EE of the D2D link is mainly determined by the location of the cellular user equipment (CUE) that shares resource with the D2D pair. Then we extend the single D2D link to multiple D2D links, and propose a location-based channel reusing algorithm. This algorithm formulates the channel reusing problem as an assignment problem, and solved it with Hungarian Algorithm. Simulation results show that the proposed algorithm can effectively improve the overall EE of the D2D system while guaranteeing the target rate of each D2D link.Secondly, the thesis introduces MIMO technology into the D2D system, and a novel interference mitigation scheme based on BS’s downlink precoding is proposed. The proposed scheme takes into account the interference mitigation for D2D users when designing the downlink precoders of the BS. It allows the transmitted signal of BS to aim at the scheduled cellular user while lying in the interference-free subspace of the BS-to-D2D channel, so as to avoid the interference to the D2D receivers. Moreover, considering the imperfect channel state information in practical system, this thesis further analyses the effect of channel estimation error on the performance of the proposed scheme. Simulation results show that substantial gain in D2D throughput can be achieved by using the proposed precoding scheme, but such gain is largely dependent on the accurate channel state information of the BS to D2D receiver.Thirdly, the D2D-assisted two-stage cooperative multicast (CM) is investigated. The thesis focuses on a new scenario, where a large number of multicast recipients are densely distributed within a small area. In such scenario, D2D multicast is innovatively employed in the retransmission stage, and a new relay selection scheme is proposed. Moreover, the optimal time allocation between the direct and retransmission stages is investigated, with the aim of maximizing the resource utilization of the two-stage CM. The time allocation problem is formulated as an optimization problem and solved by the sequential quadratic programming (SQP) method. Simulation results show that:(1) The D2D assisted two-stage CM can achieve higher cost-efficiency than the conventional one-stage multicast, and the gain becomes larger when the D2D cluster is farther from BS.(2) Different time allocation strategies should be adopted for different D2D clusters, so as to maximize the resource utilization. |
PDF Full Text Request