| Summary: | 碩士 === 長庚大學 === 電機工程學研究所 === 97 === In recent years, OFDM is an important technology in the development of wireless communication systems. It can reduce complex by utilizing the Fast Fourier Transform and combat the inter-symbol interference by using guard interval in the transmit symbols.
The multiple-input multiple-output (MIMO) is a promising technology in the wireless communication systems duo to the abilities to provide high data rate and better bit error rate. However, the MIMO-OFDM technology is very sensitive to the carrier frequency offset (CFO), since CFO would destroy the orthogonality among the subcarriers and induce inter-carrier-interference (ICI) in the received signal.
In this paper we propose a new frequency synchronization technique for MIMO-OFDM systems. In this paper we utilize space-time block code (STBC) sequences in the proposed training sequence structure. The training symbol are made by placing a data on the even subcarriers and zeros are placed on the odd subcarriers in first antenna. In second antenna, the training symbol are made by placing a data on the odd subcarriers and zeros are inserted on the even subcarriers in second antenna. The above STBC structure is then modified by our new algorithm to make a new training sequences which have periodic and symmetric properties in first antenna and second antenna, respectively. We exploit the properties of the new training sequences to obtain the correct timing and frequency offset. The CFO estimate is computed by the phase of the synchronization signal when the correct time is found.
Our algorithm will be compared with Chu, Mody, and Schenk methods, simulation results show that the proposed method would have a CFO mean square error less than 10-4 at 15 dB SNR of received signals in the multipath channel enviroments.
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