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Multipath-induced non-orthogonal inter-carrier interference mitigation for underwater acoustic orthogonal
Lianjie Wang1,2,3, Xiaoping Hong1,2,3,4, Jucheng Zhang1,2,3
1National Key Laboratory of Underwater Acoustic Technology, Harbin Engineering University, Harbin 150001, China.
Abstract:
The orthogonal frequency-division multiplexing multiple frequency-shift keying with sweep-spread carrier (OFDM-MFSK-S2C) suffers from inter-carrier interference (ICI), which is often misaligned with the orthogonal subcarrier grid (i.e., the nominal grid). To address this issue, a refined-grid intra-carrier interference mitigation (RG-ICIM) algorithm is proposed, which models non-orthogonal ICI components by subdividing the spacing of the nominal subcarrier grid. Based on the refined-grid model, Linear Frequency Modulation (LFM) preamble is utilized to estimate non-orthogonal ICI components. A mapping matrix is then constructed to link the refined-grid ICI representation to the nominal-grid transmit-symbol vector, based on which a least squares criterion is formulated to obtain the ICI mitigation-filter tapping coefficients. In addition, a simplified Cooley-Tukey Fast Fourier Transform algorithm is developed to reduce demodulation complexity. Simulation results demonstrate that the proposed algorithm mitigates ICI effectively and achieves a lower bit-error rate (BER) than conventional OFDM-MFSK in severe multipath channels. In the field test, OFDM-MFSK-S2C with the RG-ICIM achieves an average BER of 2×10-4, substantially outperforming conventional OFDM-MFSK (2.95×10-2) and nominal-grid ICI mitigation (1.69×10-2).
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