D2D And Small Cell Oriented Relay Technologies

As a new research field of changing network deployment and network architecture, wireless relay technology facilitates user equipments’access to the network via intermediate nodes, which effectively reduces the wireless channel loss, expands the network coverage, reduces cell-edge interference and enhances the system performance. Besides, relay stations have light weights, small sizes, flexible locations, and high cost performance considering deployment and maintenance. Hence, it has become one of the key technologies of LTE-Advanced system. On the other side, as important methods of shunting macro cellular data service in the future, device-to-device (D2D) communication and small cell technology will become important parts in the R12technical report proposed by3GPP in June2014. Therefore, LTE-Advanced system in the future will be heterogeneous networks in which the above three technologies coexist. There are many problems to be solved and improved on the wireless resource management in this scenario. This paper mainly researches on D2D and small cell oriented wireless relay technologies, and proposes some transmission mechanism.Firstly, the relay selection problem of relay assisted D2D system is studied. We explained a single cell model containing D2D user equipments, analyzed the interference caused by the coexistence of D2D system and cellular network and proposed a distributed relay selection method. Improper relays are eliminated according to quality of service (QoS) of cellular links. The best relay is selected by a simple distributed method among the remaining optional relays. Propagation channel and transmit power are determine during the selection process. Simulation results show that the proposed method performs much better than the method which randomly selects a relay. When the interference threshold of base station is high and there are much optimal relays, the proposed method has a close performance as the centralized optimal method.Next, the access problem of small-cell-edge macro user equipment is studied. This paper analyzes the deficiency of conventional macro cellular access of this scenario and proposes a small cell cooperative access mechanism base on device-to-device communication. Based on a path-loss model, we derived the access probability of at least one macro user equipment and the establish probability of the two hop transmission links if access completed, and proved that there is an optimal value of the user equipment selection scope for the proposed mechanism, that makes the mechanism most efficient. Simulation results show the accuracy of theoretical analysis, the high efficiency of the proposed mechanism and that the proposed mechanism brings effective enhancement of spectrum efficiency.Finally, the wireless relay technologies based on LTE-Advanced system are analyzed by simulation. We briefly summarized the physical layer for downlink and the network architecture and protocols of TD-LTE system, and their simulation realization. Then we introduced the basic architecture, simulation environment, channel model and key technologies realized of the simulation platform built by OPNET. Next we tested the simulation platform by channel calibration, and compared the results with the industrial recognized ones, which calibrates the system simulation parameters agree with the relevant protocols and standard. We used the calibrated platform to evaluate the performance of the relay station’s energy saving mechanism. Simulation results show that it can effectively reduce the system power consumption and average packet delay, but also reduce the system capacity and increase the packet loss rate to a certain extent. They also illustrate that the deployment of relay stations in the LTE system enhances the system capacity, reduces the cell-edge interference and increase the packet delay.