Abstract
Design of underwater acoustic (UWA) modems for compact-sized, underwater platforms such as autonomous underwater vehicles (AUVs) is challenging because of the practical requirement to keep an engineering balance between the performance and the system overhead. Considering this type of mobile communication scenario, Doppler spread as well as the multipath draws substantial attention in implementing the system’s design and engineering. Specifically, for a small AUV, the large computational complexity of real-time resampling for the classic Doppler correction poses significant difficulty for the limited capability of the low-cost processor. In this paper, by adopting an adjustable AD (analog-to-digital) sampling rate, a Doppler compensation approach is proposed to enable low-complexity hardware implementation. Based on this, a direct sequence spread spectrum (DSSS) acoustic modem is designed for a low-cost, small-sized AUV. Meanwhile, the performance evaluation of this acoustic modem is conducted in terms of the robustness upon varying Doppler as well as AUV integration. Finally, experimental results performed on a commercial, small-sized AUV under different speeds are reported to verify the effectiveness of the proposed acoustic modem.
Highlights
With the rapid development in underwater information acquisition and transmission, the small underwater autonomous mobile platform is drawing more and more attention from the fields of marine environmental monitoring, ocean sampling, and oceanic engineering because of its low-cost, convenience, and capability for dense deployment
Underwater acoustic communication is urgently required for many autonomous underwater vehicle (AUV) applications to allow transmission of data and control among each other [1]
It has been well recognized that multipath expansion, time-varied fading, and Doppler spreading in both time and frequency domains are challenging topics for underwater acoustic communication
Summary
With the rapid development in underwater information acquisition and transmission, the small underwater autonomous mobile platform is drawing more and more attention from the fields of marine environmental monitoring, ocean sampling, and oceanic engineering because of its low-cost, convenience, and capability for dense deployment. Among other areas of progress, He et al [6] proposed an accurate Doppler shift estimation method, which automatically matched underwater acoustic multipath channels. By directly tuning the analog-to-digital (AD) sampling rate according to the Doppler estimate, our approach significantly reduces the computational load for its implementation on small AUVs. The proposed modem utilizes a spread spectrum modulation scheme to enable robust, low data rate communication. Our approach enables the adoption of a low-cost and relatively simple processor for modem design; it is well suited to small AUVs. A sea trial as well as a lake trial has been conducted to verify the effectiveness of the proposed acoustic modem
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