The Research And Application Of Iterative Interference Alignment And Interference Neutralization In The Wideband Wireless Communication Systems

In order to meet the increasing demand for high-speed wireless applications, a variety of physical layer technologies will be combined in the future wireless communications systems, such as:Multiple-Input Multiple-Output, Orthogonal Frequency Division Multiplexing, Cognitive Radio, Ultra-Wideband. These technologies will achieve the high-speed wireless communication with no "blind spot" nor "busy area". In a multi-user wireless communication system, a plurality of users communicate simultaneously through the frequency multiplexing and spatial multiplexing to improve the system’s radio resource utilization. However, it is inevitable to cause mutual interference between users. The interference alignment (IA) technology is the latest interference management method, mainly used to resolve the interference problem between multiple users. In contrast to egoism-based approaches, IA makes the transmitters altruistically precode their signals to allow other users to perfectly cancel the interference. With IA, the entire system achieves linear capacity scaling in the presence of mutual interference. This dissertation investigates the interference alignment iterative algorithm in the future broadband wireless communication systems which uses MIMO and UWB technologies as the foundation. At the same time, this dissertation introduces UWB channel measurements and UWB channel model parameters extraction. The main contents are summarized as follows:1. For multiple-input multiple-output (MIMO) interference channel, a novel iterative algorithm for interference alignment with local channel statements is proposed. First, the dissertation proves that the interference subspace obtained by total least squares (TLS) achieve estimation error. Then, based on the subspace division, the precoder matrices are determined by "altruistic" method. Each transmitter tries to avoid the interference they caused leaking into others’desired signal subspace. Then, we analyze the convergence of the algorithm. The simulation results show that the proposed TLS interference alignment algorithm is able to achieve a lower leakage interference energy than the other algorithms at moderate signal-to-noise ratio(SNR). Meanwhile, in the high SNR scenario, the algorithm can achieve faster convergence rate and lower leakage interference.2. In the presence of the limited SNR and uncoordinated interference, the dissertation proposed a two-step algorithm based on a combination of subspace division and MMSE, which can provide improved sum rates under medium SNR conditions, particularly in the uncoordinated interference scenario. The TLS is then used to estimate the interference subspace and to compress its dimensions when we consider the noise and the uncoordinated interference as disturbances in the coordinated interference subspace. After the normal vectors of the best estimation with minimum sum squared error are attained, the MMSE method is chosen. The aim of the MMSE objective function is to minimize the sum of the Euclidean distances between the projections of the received signals in the signal subspace and the original transmitted signals. By jointly optimizes the beamforming matrices and signal subspace division, the proposed TLS+MMSE algorithm could provide flexible and adaptive solutions using transmitted power constraints. The experimental results show that the proposed algorithm outperforms the other algorithms when the uncoordinated interference is introduced. The algorithms are then compared under different uncoordinated interference power levels.3. A cooperative relay scheme is proposed to improve the outage performance of the primary transmission in Cognitive Radio networks. The secondary users (SUs) are utilized as relay nodes to decrease the retransmission number of primary user(PU). This relay scheme is based on aligned interference neutralization, and neither prior information of PU’s signals and codebooks nor initialization phase is needed. We first introduced two different channel models which is frequently used in the cognitive networks:Rayleigh channel model and UWB channel model. We firstly completed the measurements of the UWB channel’s statements in china. Then, the closed-form solutions of the maximum secondary transmission powers are derived in both Rayleigh channel and UWB channel. Additional outage probability caused by the imperfectly channel state information is then investigated. Simulation results indicate that the proposed relay scheme can provide attractive primary outage probability decrement in both prefect CSI and imperfect CSI cases.This thesis specified that the TLS-based hyperplane surface fitting algorithm has a role in promoting study of the subspace interference alignment. And the proposed interference alignment iterative algorithm also have a positive meaning in the research of interference alignment for the practical wireless system. Meanwhile, the proposed cooperative relay scheme based on interference alignment and neutralization also has a wide application prospect.