The Research And Simulation Analysis Of Precoding Based On The MIMO System

The basic features of the future wireless communication system are higher transfer rate and more reliable transmission mode. MIMO technology can obviously improve the capacity and communication quality of the system to meet the high-speed wireless business requirements. Precoding is a kind of signal preprocessing technologies. It pretreats the signals in launch end using the CSI, and the receiver can not only recover its signals, sometimes also can reduce complexity of the equipment. Precoding can reduce BER or improve the throughput of the system.This thesis, on the basic of understanding the basic principles of MIMO system and its key technologies, discusses the diversity technology and spatial multiplexing technique on multiple antennas.In the STBC system based on the diversity technique, this thesis studies that the transmitter how to use CSI to pretreat the signals in case of channel mean feedback and channel limited feedback. The precoding scheme of channel mean feedback is that, considering estimated errors and joining disturbance matrix, the transmitter determines the beam forming vector and distribution coefficient of power self-adaptively, in the conditions that total emission power is fixed, to make the BER of system minimum. The precoding scheme of channel limited feedback is that forming the optional precoding matrixs into a code-book, the receiver feedback the the index of precoding matrixs to the transmitter,In the spatial multiplexing structure, the system uses SVD after the QR decomposition to realize precoding in condition of fully known CSI. In condition that the channel existes limited rate feedback, the thesis considers the design of the precoding code-book in two methods of vector quantization and Grassmannian subspace packing. In related channel, the system designs the precoding matrix according to the known covariance information of the channel, with the minimal pair error probability for a starting point and considering its energy allocation problem.Finally, the thesis proposes a mixed STBC-VBLAST system. The system uses feature beam forming algorithm with the QR decomposition and the water-filling energy distribution principle to design the precoding matrix with the minimal pair error probability for a starting point.Using of Matlab simulation software, each precoding scheme is tested. The results show that, combining the precoding and MIMO technology, can reduce the BER of the system and improve the system performance.