Opportunistic Interference Alignment Approach In D2D Communications Underlaying Cellular Networks

As people propose the ever-increasing demands for the conmmunications performance, Device-to-Device (D2D) communications, which is an emerging technology, has attracted the attention of many scholars. The reason is that D2D can improve the spectrum efficiency of the networks and save the energy comsuption. However, with the introduction of the D2D communications, the cellular networks would receive the interference caused by D2D networks.Then, the capacity of the cellular networks would be reduced greatly. In order to improve the performance of the whole networks, this thesis focuses on the user scheduling, precoding, power allocation and so on. Also, the analysis of the user scheduling and power allocation would be shown later. Then, based on the theoretical analysis and simulation results, the superiority of the proposed schemes can be further illustrated. These schemes which are considered in different perspectives can improve the performance of the communication system, and have an important guiding significance for the specific implementation of D2D communication underlaying the cellular networks.The main innovations and contributions of this thesis are as follows:1) In consideration of the user scheduling scheme applied in the interference management, aiming to futher analyze the user selection scheme,this thesis proposes a simple user selection scheme combined with the degree of freedom for the D2D networks and the cellular networks. This scheme can guarantee the communication quality of the D2D networks and the cellular networks. Of course, this scheme only needs local channel state information(CSI), and reduces the system overhead in user scheduling. Meanwhile, the theoretical analysis of the user scheduling process is described, and the specific theoretical results are given in this thesis.2) Based on the characteristics of D2D communications, aiming to improve the sum rates of the whole networks, a novel opportunistic interference alignment scheme (OIA) is proposed. In this scheme, based on the reference signal space (RSS) broadcast by the cellular users, D2D users(DUs) are opportunistically selected to transmit. Due to RSS and CSI, the DUs take use of the scheduling metric which represents the strength of D2D interference to the cellular users, and then calculate the results. Then, the DUs are selected according to these results. In our proposed scheme, based on CSI and the RSS, this thesis proposes two different user selection strategies based on the angles between the channel state information and the reference signal space. These strategies can reduce the interference between the D2D and cellular networks. Of course, these strategies can effectively reduce the system overhead when the DUs are selected. For the scenario where the users transmit many data streams, this thesis extends our strategies and does some modification.3) Aiming to improve the energy efficiency (EE) of the D2D networks and guarantee the interference received at the cellular users is within an acceptable level, this thesis proposes a method by using Stackelberg game based on the interference pricing mechanism in D2D communications underlaying cellular networks. Unlike most of the existing methods, this thesis does not only improve the EE of the D2D networks or protect the communication quality of the cellular networks, but use interference pricing framework to jointly solve the EE resource allocation problem and the interference constraint problem in our networks. In particular, this thesis also proposes two kinds of interference pricing strategies. According to the different strategies, this thesis analyzes the Stackelberg equilibrium of the game, specially, the upper and lower boundaries of the interference price can be obtained for the first strategy, and a backward induction is used to analyze the game in the second strategy.