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Appl. Sci. 2017, 7(12), 1286; doi:10.3390/app7121286

A Novel Fractional Fourier Transform-Based ASK-OFDM System for Underwater Acoustic Communications

1
Department of Electronics and Communications Engineering, College of Engineering and Technology, Arab Academy for Science, Technology & Maritime Transport (AASTMT), Alexandria 1029, Egypt
2
Department of Computer Engineering, College of Engineering and Technology, Arab Academy for Science, Technology & Maritime Transport (AASTMT), Alexandria 1029, Egypt
*
Author to whom correspondence should be addressed.
Received: 29 October 2017 / Revised: 3 December 2017 / Accepted: 6 December 2017 / Published: 11 December 2017
(This article belongs to the Special Issue Underwater Acoustics, Communications and Information Processing)
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Abstract

A key research area in wireless transmission is underwater communications. It has a vital role in applications such as underwater sensor networks (UWSNs) and disaster detection. The underwater channel is very unique as compared to other alternatives of transmission channels. It is characterized by path loss, multipath fading, Doppler spread and ambient noise. Thus, the bit error rate (BER) is increased to a large extent when compared to its counterpart of cellular communications. Acoustic signals are the current best solution for underwater communications. The use of electromagnetic or optical waves obviously entails a much higher data rate. However, they suffer from high attenuation, absorption or scattering. This paper proposes a novel fractional fast Fourier transform (FrFT)—orthogonal frequency division multiplexing (FrFT-OFDM) system for underwater acoustic (UWA) communication—which employs the amplitude shift keying (ASK) modulation technique (FrFT-ASK-OFDM). Specifically, ASK achieves a better bandwidth efficiency as compared to other commonly used modulation techniques, such as quadrature amplitude modulation (QAM) and phase shift keying (PSK). In particular, the system proposed in this article can achieve a very promising BER performance, and can reach higher data rates when compared to other systems proposed in the literature. The BER performance of the proposed system is evaluated numerically, and is compared to the corresponding M-ary QAM system in the UWA channel for the same channel conditions. Moreover, the performance of the proposed system is compared to the conventional fast Fourier transform (FFT)-OFDM (FFT-OFDM) system in the absence and presence of the effect of carrier frequency offset (CFO). Numerical results show that the proposed system outperforms the conventional FFT-based systems for UWA channels, even in channels dominated by CFO. Moreover, the spectral efficiency and data rate of the proposed system are approximately double the values of the corresponding conventional OFDM systems for the same parameters. View Full-Text
Keywords: amplitude shift keying (ASK); carrier frequency offest (CFO); fractional Fourier transform (FrFT); orthogonal frequency division multiplexing (OFDM); underwater acoustic (UWA) channels amplitude shift keying (ASK); carrier frequency offest (CFO); fractional Fourier transform (FrFT); orthogonal frequency division multiplexing (OFDM); underwater acoustic (UWA) channels
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Ashri, R.; Shaban, H.; El-Nasr, M.A. A Novel Fractional Fourier Transform-Based ASK-OFDM System for Underwater Acoustic Communications. Appl. Sci. 2017, 7, 1286.

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