In recent years, mobile communication technology has developed rapidly and people have higher requirements for the communication quality. Addressing the problem of low communication quality in areas such as the edge of LTE-A cells, we introduce relay technology to expand the coverage area and improve the communication quality in hotspots. D2D technology can use the increasingly scarce spectrum resources efficiently and improve the utilization efficiency of communication system throughput and frequency band. Using layer 3 relay, we coexist with D2D direct users, D2D non-direct users, and cellular users to construct a communication network, and study the influence of different mode configurations on the throughput. This paper considers the combination of relay technology and D2D technology in the LTE-A cell to study and analyze the communication performance of the system. Based on the LTE-A relay cellular network system architecture and link model and the communication mode of D2D technology, we combine the D2D undirected model with the LTE-A relay cellular network to establish a D2D system model, analyze the communication process, then construct a MINLP optimization problem with system throughput as the objective function and use the method of Lagrange dual to solve it. Through theoretical derivation and simulation analysis, the throughput of the LTE-A cell constructed by the combination of D2D non-direct mode and relay technology is obtained.

In most wireless systems, the channel transmission loss of millimeter wave signals is often greater than that of traditional signals. Hybrid precoding can leverage large antenna arrays to compensate this loss and further improve the spectral efficiency of millimeter wave. This paper explores the sparsity of mmWave channel—only a few main paths are useful for the precoding procedure. This sparsity makes it possible to use a limited feedback in channel estimation. We propose a novel hybrid precoding scheme in this paper, which utilizes the main vector of the channel. We call this scheme Multiple Dimensional Scaling (MDS) hybrid precoding. On the one hand, comparing with many traditional hybrid precoding schemes with full channel information feedback, our scheme can decrease feedback overheads significantly. On the other hand, comparing with some hybrid precoding with limited channel feedback information, our scheme can improve spectral efficiency. Moreover, the simulation results show that the system spectral efficiency increases with the number of data streams significantly.

With the development of 5G technology, the demand for communication quality has shown exponential growth. Regarding the problem of low communication quality at the edge of the LTE-Advanced cellular network, we can expand the coverage and share base station traffic by introducing relay technology and D2D technology, thereby increasing the throughput of the communication system. The research background of this paper is to combine pass-through (direct) D2D mode with LTE-A relay cellular network in LTE-A cells, and then construct the MINLP optimization problem with maximizing system throughput as the objective function. The convex optimization method is used to realize the optimal allocation of power resources. The final simulation results show the growth of system throughput and user fairness.