- Volume 14 Issue 2
In underwater acoustic communication, the transmitted signals are severely influenced by the reflections from both the sea surface and the sea bottom. As very large reflection signals from these boundaries cause an inter-symbol interference (ISI) effect, the communication quality worsens. A channel estimation-based equalizer is usually adopted to compensate for the reflected signals under the acoustic communication channel. In this study, a feed-forward equalizer (FFE) with the least mean squares (LMS) algorithm was applied to a quadrature phase-shift keying (QPSK) transmission system. Two different types of equalizers were adopted in the QPSK system, namely a real-coefficient equalizer and a complex-coefficient equalizer. The performance of the complex-coefficient equalizer was better than that of two real-coefficient equalizers. Therefore, a Hilbert transform was applied to the real-coefficient binary phase-shift keying (BPSK) system to obtain a complex-coefficient BPSK system. Consequently, we obtained better results than those of a real-coefficient equalizer.
Feed-forward equalizer;Inter-symbol interference;Least mean squares algorithm;Quadrature phase-shift keying;Underwater acoustic communication
- T. C. Yang, “Properties of underwater acoustic communication channels in shallow water,” Journal of the Acoustical Society of America, vol. 131, no. 1, pp. 129-145, 2012. https://doi.org/10.1121/1.3664053
- T. B. Aik, Q. S. Sen, and Z. Nan, "Characterization of multipath acoustic channels in very shallow waters for communications," in Proceeding of OCEANS 2006 - Asia Pacific, Singapore, pp. 1-8, 2006.
- W. B. Yang and T. C. Yang, “High-frequency channel characterization for M-ary frequency-shift-keying underwater acoustic communications,” Journal of the Acoustical Society of America, vol. 120, no. 5, pp. 2615-2626, 2006. https://doi.org/10.1121/1.2346133
- J. Park, J. R. Yoon, and J. S. Park, “Frequency and temporal coherence variation for sea surface fluctuation,” Japanese Journal of Applied Physics, vol. 48, no. 7S, article ID. 07GL03, 2009.
- J. Park, K. C. Park, and J. R. Yoon, “Underwater acoustic communication channel simulator for flat fading,” Japanese Journal of Applied Physics, vol. 49, no. 7S, article ID: 07HG10, 2010.
- J. G. Proakis, Digital Communications, 5th ed. New York: McGraw-Hill, 2008.
- J. Kim, K. C. Park, J. Park, and J. R. Yoon, “Coherence bandwidth effects on underwater image transmission in multipath channel,” Japanese Journal of Applied Physics, vol. 50, no. 7S, article ID. 07HG05, 2011.
- Y. H. Yoon and A. Zielinski, "Simulation of the equalizer for shallow water acoustic communication," in Proceeding of OCEANS 1995, San Diego, CA, pp. 1197-1203, 1995.
- S. S. Haykin, Adaptive Filter Theory, 3rd ed. Upper Saddle River, NJ: Prentice Hall, 1996.
- A. B. Carlson, Communication Systems, 3rd ed. New York: McGraw-Hill, 1986.
- F. B. Jenson and W. A. Kuperman, Computational Ocean Acoustics. New York: AIP Press, 1994.
- 1. Hilbert-Transform-Based Accurate Determination of Ultrashort-Time Delays in Terahertz Time-Domain Spectroscopy vol.7, pp.5, 2017, doi:10.6109/jicce.2016.14.2.078