| Orthogonal frequency division multiplexing(OFDM) is a multi-carriermodulation technology, and it is obtained more and more attention due to itsadvantages such us high spectrum efficiency and strong anti multipath faidngability. Recently, OFDM technology is applied to wireless communication, andwireless local area networks (WLAN), and is adopted as physical layer standardin IEEE802.11a. Now, OFDM technology is regarded as the core technology ofmobile communications beyond3G. And people are attempting to apply OFDMtechnology on low-voltage power line carrier communication. In recent years, themerger of MIMO and OFDM becomes the focus of study. However, both OFDMsystems and MIMO-OFDM systems are very sensitive to time and frequencysynchronization errors. If there are synchronization errors in OFDM systems orMIMO-OFDM systems, they will introduce inter-symbol interference, evenintroduce inter carrier interference, and will destroy the orthogonality betweenthe subcarriers. So it is necessary to estimate timing synchronization errors andcarrier frequency synchronization errors more accurately for both OFDM systemsand MIMO-OFDM systems.Firstly, analyze the influence to OFDM systems performance which arecaused by synchronization errors. Timing synchronization error and carrierfrequency offset error are deeply analyzed. And the effect of timingsynchronization error and carrier frequency offset error to the performance ofOFDM systems is given.Secondly, study on the timing synchronization algorithm based on trainingsequence. An improved algorithm based on novel training sequence is proposed by studying on S&C algorithm and Minn algorithm. The proposed method canimprove the synchronization performance of OFDM systems.Thirdly, research on the timing and frequency synchronization based oncyclic prefix. The influence of the length of cyclic prefix to ML algorithmsynchronization performance has been studied. On the basis, an improvedalgorithm with variable length of cyclic prefix is proposed. The proposedalgorithm has better synchronization performance than ML algorithm at lowsignal to noise ratio. The difference timing and frequency synchronizationalgorithm based on cyclic prefix for OFDM systems is proposed amied at theproblem that ML algorithm is not suitable for synchronization estimation inmultipath channel. The proposed algorithm can realize timing and frequencysynchronization estimation in multipath channel.Finally, study on timng and frequency synchronization algorithm in MIMO-OFDM systems. MIMO channel is multiple-input multiple-output channel;generally, it can be classified into two categories: localized MIMO channel anddistributed MIMO channel.An synchronization algorithm which has four steps isproposed aimed at the MIMO-OFDM systems in localized MIMO channel. Theproposed algorithm which has a set of short training sequences and two longtraining sequences has good synchronization performance for timing andfrequency synchronization. |
PDF Full Text Request