Research On Channel Estimation Technique For MIMO-OFDM Systems

With the rapidly increase of wireless data and multimedia application in recent years, research on the next generation(4G) mobile communication has being widely and deeply developed. The 4G communication system is a wireless network with high spectrum efficiency and high rate in limited bandwidth, and it supports high bit rate data transmission for many services. With the parallel modulation, orthogonal frequency-division multiplexing (OFDM) can change a frequency selective fading channel to be several flat fading channels, thus improving the transmission efficiency tremendously. Multiple-input multiple-output (MIMO) system which utilize multiple transmit/receive antennas can significantly increase the channel capacity, greatly improve the spectrum efficiency.Combination of OFDM and MIMO techniques can take advantages of the merit of both techniques, keeps the robust performance in the frequency-selective fading channel by OFDM and enhance system capacity enormously by MIMO.MIMO-OFDM technology relies on accurate channel state information (CSI) to be available at the receiver. Channel estimation is critical in the design of MIMO-OFDM systems for coherent detection and decoding. Therefore, this thesis has investigated the channel estimation techniques for MIMO-OFDM systems.In chapter 1, the background and development of OFDM and MIMO technologies are introduced, as well as the channel estimation technology profile.In chapter 2, the characteristics of mobile communication channel are discussed. Firstly the influence factors of signal strength are discussed, then the definition and classification are introduced.In chapter 3, the OFDM, MIMO and MIMO-OFDM system are introduced, besides, the introduction of space-time coding in MIMO system is presented, and the significant parameters in OFDM systems are introduced.In chapter 4, the channel estimation techniques for SISO-OFDM systems are investigated, mainly towards block-type, comb-type and spread-type pilots channel estimation, a survey of recent pilot assisted estimation algorithms is provided, including 4 pilot estimation algorithms and 6 interpolation algorithms. Besides, the influence to transmit performance by pilot-pattern is also studied.In chapter 5, the channel estimation techniques for MIMO-OFDM systems are investigated. In the frequency-domain, the design of pilot-pattern is studied with computer simulation. In the time-domain, we provide and simulate a design of main-tap algorithm to simplify the estimators, and a design of optimal training symbols to optimize channel estimation performance. Then we propose a channel estimation scheme using both two algorithms discussed above adding decision feed back technology in time-domain. Consequently, based on the research results presented above and 802.16e WiMAX standard, the complete simulation and performance evaluation of MIMO-OFDM system channel estimation techniques are provided.In last chapter, the conclusion of thesis is given, as well as the necessary future work.