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Study Of Channel Estimation And Synchronization For MIMO-OFDM Systems

Posted on:2011-06-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y ZhangFull Text:PDF
GTID:1118360332958019Subject:Information and Communication Engineering
Abstract/Summary:PDF Full Text Request
The target of next generation wireless mobile communication is to obtain higher efficiency of spectrum. In the wireless communication with the limitation of bandwidth and power, the implementation of MIMO technique can achieve high efficiency of spectrum. At the same time OFDM technology has the property of high tolerance to multi-path fading and low complexity to receiver design, therefore, the combination of these two technologies, that is MIMO-OFDM, can further be efficient for wideband multimedia transmission because of its high ability of anti-fading, high channel capacity and high bit-rate data, and widely be regarded as one of the most promised techniques for 4G wireless communication, which is also to be the focus research field in the future wireless mobile communication.Synchronization is the primary procedure for signal processing, which influences the performance of following baseband signal processing. MIMO-OFDM system is sensitive to synchronization errors. Very small carrier frequency offset (CFO) may degrade system performance severely. Correct symbol timing and precise CFO estimation are necessary for MIMO-OFDM systems.At the same time, channel estimation plays a very important role in MIMO-OFDM system and that is required for coherent detection and space-time decoding in MIMO-OFDM systems. Channel estimation and system synchronization of wireless MIMO-OFDM system are discussed in this dissertation based on the above consideration. The main achievements are listed as follows:1. Based on the time-varying channels, an interpolation-based MIMO-OFDM channel estimation algorithm is discussed. The system model of MIMO-OFDM over time-varying channels is acquired, and a novel channel estimation method which adapt to time-varying channels is proposed. Because channel parameters change rather slowly with respect to subcarriers, and the intercarrier interference (ICI) and additive white Gaussian noise (AWGN) in the received signal appears as fast-changing function of subcarriers, therefore, the ICI and AWGN in the pilot subcarriers are reduced by lowpass filtering which employed by the proposed method, the performance of the system is effectively improved.2. In order to improve the performance of space-time block coded MIMO-OFDM channel estimation, a two-step channel estimation method is proposed in this paper. The Minimum Mean Square Error (MMSE) channel estimation algorithm is used to estimate initial channel parameter values in the first step and these values are used to obtain more accurate values by the proposed method in the second step, so the performance of channel estimation is improved. Simulation results show that the performance of the two-step channel estimation method greatly outperforms compared to the LMS channel estimation algorithm and the RLS channel estimation, while largely decreases the computational complexity and consumption.3. Starting from the time-domain signal model of MIMO-OFDM, this paper analyzes the influences of all kinds of errors on the received signal. Then, in order to improve the accuracy of the timing synchronization which obtained by using the conventional method and the utilization of the frequency spectrum, an efficient timing and frequency offset estimation method for MIMO-OFDM systems is presented. This algorithm constructs a special training sequence to gain a better symbol timing performance, and meanwhile requiring only one training symbol, this algorithm can efficiently estimate integer frequency offset and fraction frequency offset. Comparing with conventional algorithms, the proposed method reduces the number of the training symbols, and improves the utilization of the frequency spectrum. Simulation results show that with channel AWGN and Jake, the scheme gives very accurate estimates of symbol timing and carrier frequency offset and provides a very wide range of acquisition for the carrier frequency offset, outperforming other available methods.4. IEEE.802.11a Physical Layer Standard is introduced, and the symbol timing algorithm which is suit for IEEE802.11a is discussed. Then, in order to improve the accuracy of the symbol timing synchronization which obtained by using the conventional method, a modified preamble structure for MIMO-OFDM symbol timing synchronization is proposed. The proposed method creates a sharp fall in the delayed correlation of the samples at the last short preamble period by phase reversing the first half of the last short preamble samples and hence helps more reliable estimation of the end of the short preamble or the start of the long preamble boundary especially under high time dispersive channel. Analytical and simulation results show that the proposed timing algorithm can fulfill timing synchronization and has a higher precision than the traditional method.
Keywords/Search Tags:Multiple-Input Multiple-Output, Orthogonal Frequency Division Multiplexing, Synchronization, Channel estimation
PDF Full Text Request
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