Linear Pre-coding Technology Based On Wireless Mimo / Ofdm Communication System

Wireless MIMO (Multiple Input Multiple Output, MIMO) communication system, which uses multiple transmitting and receiving antennas to transmit and receive data, is able to combat multi-path fading in the hash wireless communication environment. Moreover, under the band width and power constraint, the capacity of a MIMO system is linear proportional to the minimum number of the transmitting and receiving antennas. Since the spectrum efficiency is improved significantly by the MIMO technology, it has been widely accepted as the core technology of the B3G or 4G wireless communication.However, due to the frequency selective fading channel, the wireless MIMO communication system can not combat the ISI (Inter Symbol Interference, ISI). To solve the above mentioned problem, the OFDM (Orthogonal Frequency Division Multiplexing, OFDM) is applied in the system, which may face the frequency selective fading channel. Compared with MIMO, the OFDM technology has higher spectrum efficiency and is stronger in combating channel fading caused by multi-path, therefore OFDM technology has been accepted as another very important technology of the physical layer for the future wireless communication system.Linear precoding technology, which makes use of the CSI (Channel State Information, CSI) to equalize the channel, even parallel the channel if perfect CSI is available at the transmitter, is able to improve the capacity or the reliability of the system, or enhance the coverage of a cell, and etc. The precoding technology is usually implemented in the base station for the downlink, therefore the complexity of decoding at the terminal can be reduced, and the endurance of the battery is extended. For those benefits can be acquired by precoding, the precoding technology combined with MIMO or MIMO-OFDM technology has been written in the standard of the 3GPP (3rd Generation Partnership Project, 3GPP) LTE (Long Term Evolution, LTE).In Chapter two, we briefly introduced the way transmitter gets the CSI, the framework of a precoding system, and how to design the precoder. Due to MIMO system the CSI always contains the amplitude and the phase information, the amount of feedback for precoding is too huge to overwhelm the feedback link, especially when OFDM is used. So that, precoding becomes hard to implement in the practical wireless communication. Based on the observation, in this dissertation we mainly focused on reducing the data rate of the feedback, for instance the limited feedback precoding technology.In Chapter three, subspace tracking algorithm is introduced to further reduce the amount of feedback bits, which based on the correlation of frequency response between adjacent subcarriers in the OFDM system. After analyzing the subspace tracking method, we proposed a novel way to generate precoding codebook, which is rotation of the base matrix when generating precoding codebook.In Chapter four, we use math works to analyze the most important step in subspace tracking algorithm. Based on the analysis, we proposed a novel distance, the Matrix Euclidian distance to be the metric used in subspace tracking. The novel distance outperforms the original one proved by numerical simulations.Due to the correlation of channel, when the channel is within the coherence time, we improve the subspace tracking to implement in the time domain. The proposed the time domain tracking algorithm has lower feedback rate and better performance when the amount of feedback is same.Finally, some conclusion of the whole dissertation is drawn, and the further research issues and possible direction are pointed out.