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Research on Doppler Estimation Technology for OFDM in Underwater Acoustic Communication

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Tutor: ZhaoAnBang
School: Harbin Engineering University
Course: Underwater Acoustics
Keywords: orthogonal frequency-division multiplexing (OFDM),Doppler estimation,thereplica
CLC: TN919.3
Type: Master's thesis
Year:  2012
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In order to achieve the credibility high speed data transmission and reduce theinter-symbol interference because of the multichannel delay, OFDM (orthogonalfrequency-division multiplexing) has been gradually applied in underwater communicationfrom in the late part of last century. Whereas, the obvious Doppler restrict the OFDM systemin underwater communication thanks to rigorous orthogonality, and the complicated fastchanged channel as well as comparative movement between transmitter and reciever. TwoDoppler estimation algorithms focus on OFDM in underwater communication are researchedin this paper. The performances of the two algorithms are validated, and the advantage andshortcoming as well as befitting condition of two algorithms are compared and analyzed bythe simulation and lake experiment.First, in order to avoid adding a mass of assistant data as a result of synchronization,Doppler estimation and channel estimation, the replica correlation Doppler estimationalgorithm is studied. The Linear frequency modulation signal is set so that it can completeDoppler estimation symbol by symbol and be the pilots for channel estimation besides it candetect frame synchronization location. Compared to frame structure of no reusing threefunctions, this algorithm is validated for improving communication rate through formuladeduction and simulation. Second, the null subcarriers algorithm is researched. The energy ofnull subcarriers as the target function is used to facilitate Doppler factor. Speed is searched inevery symbol, and only the null subcarriers location energy is worked out by DFT (discreteFourier transform) with this speed in every searching. The influence of speed search length,multipath channel, noise and subcarrers space to the estimation precision are emulated andanalyzed. Finally, the same experimental data are estimated and compensated based on thetwo algorithms, and error bit rates and output scatter pictures are compared. Acording to theresults, the replica correlation algorithm is simple and has the higher communication rate butlimitative in fast time-varying channels. The null subcarriers algorithm is accurate and stablebut complex, at the same time, its communication rate and precision are affected by the nullsubcarriers. The results of the simulation and experiment show that the two algorithms havetheir applied values in different conditions.
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