Research On Precoding And Coordinated Multi-Point Transmission Technologies In Wireless MIMO Systems

Multiple-input multiple-output (MIMO) technology can significantly improve the capacity and spectrum efficiency of wireless communication systems by spatial multiplexing. But it will cause serious interferences among spatial signals at the same time. MIMO pre-coding is applied at transmitting end to eliminate spatial signal interference and reduce the complexity of signal detection at receiving end. Furthermore, coordinated multi-point (CoMP) transmission is able to solve the problem of inter-cell interference and improve the spectrum efficiency and customer experience of cell edge users significantly.This dissertation focuses on MIMO pre-coding and CoMP, which is composed of three parts:The first part concentrates on MIMO pre-coding technology. Tomlinson-Harashima pre-coding (THP), as one promising type of nonlinear pre-coding schemes, is further studied based on the summarization and comparison of existing linear pre-coding and nonlinear pre-coding algorithms and a novel THP algorithm is proposed based on the lattice reduction technique. It orthogonalizes the channel matrix of MIMO communication system by applying lattice reduced technique and the performance of traditional THP algorithm with bad channel orthogonality is improved as a result. Both the theoretical analysis and simulation results indicate that the proposed algorithm could improve the bit error rate as well as the fairness between users while maintaining the original complexity, exhibiting better performance than sorting algorithm. Moreover, a realistic MIMO transmission system with high reliability is constructed using the proposed pre-coding algorithm with the system frame structure and transmission flow established.The second part describes the research and evaluation of CoMP transmission technology in single user scenes. The analysis of coherent and incoherent Joint Transmission (JT) is represented and the simulation result shows the feasibility of different CoMP realization schemes, as well as its advantages over single cell MIMO technology in improving system throughput. Corresponding modified algorithm is put forward aiming at the problems of local pre-coding and single frequency network (SFN) pre-coding included in incoherent JT. An improved local pre-coding scheme based on layer swapping is proposed to eliminate the inter-layer interference and two improved SFN pre-coding schemes are put forward to solve the uncertainty when the channels are merged. These two schemes could be described as to eliminate the uncertainty by pulling in phase parameters as well as changing the mapping relationship between transmitted data and antennas. Theoretical analysis and simulation results show that the proposed schemes can improve the spectrum efficiency of cell edge users significantly in either coherent or incoherent, either low or high rank channels.The third part of this dissertation mainly focuses on CoMP interference elimination method in dual-polarized channel. Aiming at the deficiency of the existing feedback mechanism, a novel cooperation interference elimination method is proposed after investigating the interference processed at the receiver in dual-polarized channel without extra feedback. A good interference elimination effect can be achieved with a little pre-coding structure information of interactions among transmission nodes. And this method could improve system performance and reduce the feedback significantly at the same time. Link level simulation results represents this scheme could greatly improve the SINR gain while system level simulation demonstrates that in overcoming inter-cell interference and improving system spectrum efficiency, this scheme is also proved to be effective.