Research On Signal Space Alignment For Network Coding In Wireless Communication Networks

Capacity is the tightest upper bound on the rate of information that can be reliably transmitted over a communications system. It is recognized as one of the most important index of one system. As known that Multiple-Input Multiple-Out-put (MIMO) and Two-Way Relaying (TWR) are key technologies can increase capacity without increasing of the wireless resource or transmission power. In the Mulit-User (MU) system, the new Multiple Access (MA) technologies are introduced to joint with the MIMO and TWR for improving the spectrum efficiency and satisfying the future communication networks.Benefiting from the multiple antennas at nodes, MU-MIMO TWR system obtains the Multiplexing Gain (MG) and Diversity Gain (DG). Signal Space Alignment (SSA), which is one of the new MA technologies, is utlizied to make the paired signal aligned into the same subspace for network coding in the MU-MIMO TWR system, which reduces the signal dimensions and improve the system throughput.For the last years, there are so many research about the Signal Space Alignment for Network Coding (SSA-NC), most of which focus on the symmetrical channel system, i.e., all users utilize the same modulation scheme. However, due to the different channel qualities, the data rates of different users are unlikely to be identical and they use different modulation schemes in many applications. Therefore, the SSA-NC in the asymmetric channel MU-MIMO TWR system is investigated in this thesis. Furthermore, the SSA-NC based on the Success Interference Cancellation (SIC) receiver in MU-MIMO TWR systems is also investigated. Overall, the main contributions and innovative research findings are listed as follows:1The utilization of SSA-NC technology in the asymmetric channel MU-MIMO TWR, which has not been studied yet, is investigated. According to the type of the paired users, the system is divided into two kinds:one is the asymmetric channel MU-MIMO X network, the other is the asymmetric chennal MU-MIMO Y network. The TWR consists of two phases:multiple access channel (MAC) phase and broadcasting channel (BC) phase. For the asymmetric channel system, the protocol at the relay is the Analog Network Coding and Decode-and-Forward (ANC-DF).Provided that BPSK and QPSK are utilized, the ANC-DF remapping strategy and decoding rules for the asymmetric channel MU-MIMO X channel networks and the asymmetric channel MU-MIMO Y channel networks are proposed respectively. The feasibility condition, achieved Degree of Free (DoF) and the theoretical Bit Error Rate (BER) of the two systems are analyzed. The simulation results verify the theoretical derivations.2Since the ANC-DF remapping strategy for the asymmetric channel MU-MIMO system with BPSK and QPSK could improve the system performance obviously. It is promised to improve the performance of the generalized asymmetric channel MU-MIMO system. According to the channel quality, users select appropriate modulation schemes adaptively. Based on the Exclusive Law (EL) and the rule of maximizing the minimum Euclidean distance, a design scheme of ANC-DF remapping strategy is proposed. In the practical communication scenarios, the proposed design scheme is flexible enough to the generalized asymmetric channel MU-MIMO system.3In order to optimize the wireless resource, the SIC receiver is utilized joint with the SSA-NC technology in the MU-MIMO system. Based on the power diversity, the interferences in the aligned signals is cancelled successively by the SIC receiver. The feasibility condition of the proposed system is analyzed. The SIC receiver joint with the SSA-NC technology can not only achieve a high system spectral efficiency, but also fulfill relay minimum antenna requirements. Thus, it makes energy-efficient communications more reasonable.