Abstract
Linear chirp spread spectrum technique is widely used in underwater acoustic communication because of their resilience to high multipath and Doppler shift. Linear frequency modulated signal requires a high spreading factor to nearly reach orthogonality between two pairs of signals. On the other hand, nonlinear chirp spread spectrum signals can provide orthogonality at a low spreading factor. As a result, it improves spectral efficiency and is more insensitive to Doppler spread than the linear counterpart. To achieve a higher data rate, we propose two variants (half cycle sine and full cycle sine) of the M-ary nonlinear sine chirp spread spectrum technique based on virtual time-reversal mirror (VTRM). The proposed scheme uses different frequency bands to transmit chirp, and VTRM is used to improve the bit error rate due to high multipath. Its superior Doppler sensitivity makes it suitable for underwater acoustic communication. Furthermore, the proposed method uses a simple, low-power bank of matched filters; thus, it reduces the overall system complexity. Simulations are performed in different underwater acoustic channels to verify the robustness of the proposed scheme.
Highlights
Underwater acoustic communication in the recent past has attracted many researchers because of its application going beyond military uses such as communication between autonomous underwater vehicles (AUVs) for data collection and ocean exploration [1, 2]
The results show that binary orthogonal keying (BOK) full period sine chirp is orthogonal at low spreading factor
To increases the data rate of the underwater communication system and to solve the problem of high Spread factor (SF), spectral efficiency, and inter-symbol interference caused by underwater acoustic channels, M-ary Sine Chirp Spread Spectrum (MS-CSS) based on virtual time-reversal mirror (VTRM) is proposed in this paper
Summary
Underwater acoustic communication in the recent past has attracted many researchers because of its application going beyond military uses such as communication between autonomous underwater vehicles (AUVs) for data collection and ocean exploration [1, 2]. The underwater acoustic channel is quite challenging compared to traditional terrestrial communication because of the low sound speed of nearly 1500 m/s, high multipath environment, inherit time-varying nature of the ocean, and vehicles’ movement adds ups the Doppler effect [3], physical layer design is difficult and designing routing protocol for underwater wireless sensor networks (UWSNs) is quite challenging [4] To counter these challenges, researchers have raised many waveforms and modulation schemes. To increases the data rate of the underwater communication system and to solve the problem of high SF, spectral efficiency, and inter-symbol interference caused by underwater acoustic channels, M-ary Sine Chirp Spread Spectrum (MS-CSS) based on VTRM is proposed in this paper. The nonlinear sine upchirp and downchirp is used to represent data bits, and M-ary technique is utilized to achieve a higher bit rate by transmitting at different frequency bands, whereas correlators are used to detect the symbols.
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