Precoding For MIMO Systems

Multiple Input Multiple Output (MIMO) is implemented with multiple transmitting antennas and multiple receiving antennas to send and receive datas. And wireless communication systems using MIMO are called MIMO systems. Without increasing the system bandwidth and transmitting power of the antennas, this method can increase channel capacity linearly as the antenna number increases. In essence, MIMO technology could provide spatial diversity and spatial multiplexing for wireless communication systems. Hence, MIMO has become the key technology of the fourth generation (4G) mobile communications. However, multi-antennas transmission is bound to increase the interference between multiple users, and the interference between muti-users is the main factor affecting the channel capacity of MIMO systems. Pre-coding technology can effectively eliminate the interference between muti-users; hence, it becomes one of the hotspot in MIMO research field at present. The Pre-coding technology is to conduct a pre-processing at the transmitter, aim to adjust the transmiting strategy to the corresponding channel environment by using channel state information (CSI), it can enhance the performance of MIMO systems. This paper focuses mainly on the pre-coding technology in MIMO system.This paper firstly introduces the development of wireless communication and the research background, then introduces the propagation characteristics of wireless channel and the common wireless channel models, and highlights the signal model and the derivation of channel capacity of MIMO system.Then, in the third chapter, this paper first concludes the exiting pre-coding technologies, including linear pre-coding based on zero-forcing criterion, linear precoding based on MMSE criterion, linear pre-coding based on singular value decomposition (SVD) and non-linear pre-coding of dirty paper coding (DPC), then introduces the current common precoding algorithms like block diagonalization (BD) algorithm and Tomlinson-Harashima pre-coding (THP) algorithm with the simulation results and analysis.Chapter IV is the key part, in this part, the paper focuses on the the limited feedback precoding method:introducing the general procedures of the limited feedback precoding method; introducing the principle of the quantization of channel state information (CSI) and the criterion of codebook design; introducing a Per-User Unitary and Rate Control (PU2RC) algorithm; proposing an improved quantization method of CSI which greatly reduces the quantization error as the number of antennas increasing; proposing an improved PU2RC method which could greatly improve the system performance by expanding the scope of the schedued user at the transmitter based on the use of pre-designed relationship table between the codebook vectors.At the end of this paper, there is a summary of the entire text. What remains to be done in the next step and the future research directions are also given.