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Research On Synchronization Algorithms In MIMO-OFDM Systems

Posted on:2013-02-05Degree:MasterType:Thesis
Country:ChinaCandidate:M M LiuFull Text:PDF
GTID:2218330362962871Subject:Communication and Information System
Abstract/Summary:PDF Full Text Request
Orthogonal frequency division multiplexing (OFDM) is a highly efficient datatransmission technology for its robustness to frequency selective fading and highspectral efficiency. Multiple-input multiple-output (MIMO) can significantly increasesystem capacity. MIMO-OFDM system has become one of the most promisingtechnologies in the next generation wireless communication systems. However, bothOFDM and MIMO-OFDM systems are very sensitive to symbol timing offset andcarrier frequency offset. Timing errors will lead to inter-symbol interferences, whilefrequency offsets will cause inter-carrier interferences. In this thesis, synchronizationsfor OFDM and MIMO-OFDM systems are studied. The main achievements areoutlined as follows:Firstly, the research on the data-aided synchronization algorithms has beenstudied.An improved timing and frequency synchronization method is proposed toavoid the timing metric plateau inherent in the conventional synchronization methods.A new training sequence is designed in the proposed method and the correspondingtime metric is given based on the new training sequence. The proposed methodeliminates the ambiguity which occurs in conventional algorithms, so it has bettersynchronization precision. Furthermore, the integer frequency offset can be obtainedin time domain and the computation complexity is reduced.Secondly, the research on timing synchronization algorithms for MIMO-OFDMsystems in multi-path fading channels is analyzed. A timing synchronization schemeusing constant amplitude zero auto correlation (CAZAC) sequence as trainingsequence is proposed. The cross correlation between local sequence and the receivedsignal and the symmetrical correlation of the received signal are calculatedrespectively, and then they were combined together to detect the timing offset of eachtransmitter element. Furthermore, multi-path backward searching technique isemployed at the receivers to cope with the situation where the first path is not thestrongest. The threshold is variable in order to guarantee acceptable synchronization performance.Thirdly, the research on timing synchronization and frequency synchronizationalgorithms for distributed MIMO-OFDM systems has been investigated. To addressthe problem of time and frequency offset estimation for MIMO-OFDM systems, ajoint time and frequency synchronization algorithm based on CAZAC sequence isproposed. The proposed method not only has a significantly higher synchronizationprobability than conventional algorithm but also can estimate the frequency offsets ofall the transmitter and receiver pairs.
Keywords/Search Tags:orthogonal frequency division multiplexing (OFDM), multiple-input multiple-output (MIMO), symbol timing synchronization, carrier frequency synchronization
PDF Full Text Request
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