Software-defined underwater acoustic networks: toward a high-rate real-time reconfigurable modem

We review and discuss the challenges of adopting software-defined radio principles in underwater acoustic networks, and propose a software-defined acoustic modem prototype based on commercial off-the-shelf components. We first review current SDR-based architectures for underwater acoustic communications. Then we describe the architecture of a new software-defined acoustic modem prototype, and provide performance evaluation results in both indoor (water tank) and outdoor (lake) environments. We present three experimental testbed scenarios that demonstrate the real-time reconfigurable capabilities of the proposed prototype and show that it exhibits favorable characteristics toward spectrally efficient cognitive underwater networks, and high data rate underwater acoustic links. Finally, we discuss open research challenges for the implementation of next-generation software-defined underwater acoustic networks.

Introduction

Underwater acoustic networks (UANs) are an emerging research topic because of the key role that this technology will play in military and commercial applications including disaster prevention, tactical surveillance, offshore exploration, pollution monitoring, and oceanographic data collection. A key challenge in the design of UANs stems from the characteristics of the underwater acoustic (UW-A) channel, which exhibits high path loss, noise, multipath, high and variable propagation delay, and Doppler spread. Therefore, reliable communication links are practically feasible only at low data rates. Additionally, the propagation challenges in the underwater environment result in temporally and spatially varying UW-A channel coefficients, which drives research efforts toward the design of specialized protocols at different layers of the network protocol stack - often with a cross-laver aooroach.