Research Of Interference Alignment In Supporting D2D Wireless Network

Device-to-device(D2D) communication which is considered as one of the candidate technologies of 5G due to the properties of high date rate, low communication delay, and expansion of cellular communication. The spectrum sharing between cellular users and D2 D users, and among D2 D pairs are the main research direction, and consequently it leads to serious co-channel interference. Therefore, the research of interference management scheme in D2 D communication is promising.The existing schemes take the flexible solution of interference alignment as the constraint conditions for D2 D grouping, and the corresponding scheme for the application of adaptive antenna array in D2 D communication has not been proposed. Therefore, in this thesis, taking the flexible solution of interference alignment and the practical number of D2 D pairs in the cell as the constraint conditions for D2 D grouping, and then considering the vector angle and distance factors between D2 D group and cellular user as the decision conditions to choose the optimal cellular user for wireless resource sharing with D2 D user, which can achieve the minimum of mutual-interference between cellular users and D2 D users. The simulation results show that the proposed scheme can improve the system throughput by 8.3% and 23.8% compared with the resource sharing schemes based on distance and random.Focusing on the application of interference alignment, and when performing the power allocation for D2 D users in D2 D group, the existing algorithm is not precise to solve the transmitting and receiving pre-coding matrix by using the minimum interference leakage criterion, and it's not optimal to solve the power allocation matrix by using the evaluation iteration, i.e., amplification method. Therefore, in this thesis, the minimum mean square error is utilized to solve the transmitting and receiving pre-coding matrix, which can obtain more precise results, and furthermore the Lagrange duality is used to solve the optimal power allocation matrix. The simulation results show that in the case of satisfying the pre-set communication rate, the proposed algorithm can effectively reduce D2 D user's transmitting power, i.e., reduce the interference from D2 D users to cellular users as compared to the existing algorithm.The existing interference alignment algorithms based on feedback in D2 D communications have some drawbacks such as large feedback overhead and mutual-coordination overhead among multiple nodes. Therefore, in this thesis, using the concentration node to independently calculate the solution of interference alignment, and thereby reduce the feedback overhead and mutual-coordination overhead among transmitters. Furthermore, using the discovery messages of D2 D discovery scheme to estimate the channel state information among D2 D pairs, and then send these feedback information to base station, which can further lower the feedback overhead. The simulation results show that the concentration feedback scheme lowers the feedback overhead compared with the full-feedback scheme.