Multi-carrier communication over time-varying underwater acoustic channels

• Online Access: http://hdl.handle.net/2047/D20315047

This thesis focuses on use of orthogonal frequency division multiplexing (OFDM) for underwater acoustic (UWA) communications. OFDM offers many advantages such as its robustness against the frequency selectivity of the multipath channel for time invariant channel. However, UWA communications presents some severe challenges towards OFDM data detection performance. One of the most prominent factor is the Doppler effect, which causes the inter carrier interference (ICI) and degrades the performance significantly. In this thesis, we focus on the method called Partial FFT (P-FFT) demodulation to mitigate the ICI. This method focuses on pre-FFT signal processing and tries to mitigate the Doppler effect before it has been smeared in an irreversible manner by conventional demodulator. In the thesis we present the results of applying the P-FFT demodulation to the signals recorded during the 2010 Mobile Acoustic Communications Experiment (MACE'10). The receiver consists of two stages. In the first stage, the receiver combines the P-FFT demodulation outputs using the recursive least square (RLS) algorithm to obtain a signal with suppressed ICI. For coherent detection, the second stage includes channel estimation using the least squares and matching pursuit algorithms. We also compare the performance with differentially coherent detection combined with P-FFT demodulation. Results show coherent detection using P-FFT is able to compensate the Doppler induced variations and offers a viable option for achieving high data rate underwater communication.