Wide-ranging applications for underwater acoustic communication are attracting attention. However, the challenges of underwater acoustic communications make it necessary to advance communication techniques significantly. Underwater networks with wider coverage areas and more reliable communication links may be possible with the distributed deployment of several reception nodes. Using Single Input Multiple Output (SIMO) systems, power, and bandwidth resources can be utilized effectively without compromising spectral efficiency. In this work, we propose a communication system that employs software- defined distributed SIMO networking to exploit the spatial diversity of multiple receiver nodes for high data rates and reliable communication. To take advantage of spatial diversity, we develop and implement a software-defined architecture for the maximal-ratio combining receiver. Then, we conduct a thorough experimental evaluation in ocean environments for various subcarrier bandwidths and constellations using three distributed receivers. Our results show that our proposed distributed SIMO system, for both 1x2 and 1x3 settings, outperforms individual receiver modems in terms of bit error rate (BER) performance by 95.20% and 99.57%, respectively.

Underwater acoustic communication and networking have been instrumental in enabling various commercial and military applications such as underwater surveillance, environmental monitoring, data-driven intelligent aquaculture, and unmanned underwater vehicles. However, the development of an underwater communication and networking system poses significant challenges due to spatially and temporally varying underwater acoustic channels. These channels are subject to severe multipath propagation and the Doppler effect, which can impose frequency-dependent distortions on underwater acoustic signals through frequency shifts and spreading. In high-frequency underwater acoustic communication systems, the Doppler effect is amplified, making its estimation and compensation even more challenging. In this paper, we present a detailed set of field experiments characterizing the Doppler effect in a high-frequency underwater acoustic channel. We also introduce a multicarrier communication system incorporating a Doppler estimation and compensation method. Through extensive field experiments, we quantify the performance of the Doppler estimation and compensation technique over high-frequency channels.

Carrierless Amplitude and Phase (CAP) modulation has been widely used in the emerging visible light communication (VLC) paradigm. Compared to other modulation schemes, CAP is in fact known to be comparatively easy to implement, to have lower computational complexity, high spectral efficiency, and superior noise performance. However, as of today, how to select optimal parameters in CAP links for a desired target bit error rate (BER) performance and spectral efficiency requirements is still an open problem, because of the absence of closed-form expressions for the bit error probability under different signal-to-noise ratio (SNR) conditions. In this article, we present a comprehensive analysis on the impact of different CAP parameters on the bit error probability under different noise levels. We first describe the system model and derive a theoretical expression for the bit error rate of a CAP-modulated communication system. Then, we present detailed simulation and experimental results for different CAP parameters. The derived theoretical expression is also validated through simulations and experiments for each different CAP parameter. Then, with this expression, we show how to select optimal link parameters for different noise levels, by maximizing the spectral efficiency while keeping the BER lower than a predefined threshold.

Underwater vehicles (UVs) are becoming essential for a vast range of novel commercial, scientific and military applications. These include seabed exploration, monitoring of critical infrastructure and resources, and coastal surveillance. However, usage of UVs is currently beset by limitations preventing them to carry critical equipment, such as agile wireless communication systems, which would facilitate and enable those applications. To overcome these limitations, in this paper we present the design blueprint and evaluation of a wireless UV, obtained by integrating a custom software-defined underwater acoustic networking platform integrated to a UV. We first describe the integration of the platform with a commercially available UV. We then present results from experimental campaigns at sea using our wireless UV to generate datasets for studying the Doppler effect due to mobility. Our results indicate the effectiveness of our design for ease of deployment and dataset generation.

Autonomous networks of sensors, unmanned aerial vehicles (UAVs) and unmanned underwater vehicles (UUVs) will play a vital role in scenarios/applications where a plethora of distributed assets across multiple domains – air and water - operate in unison to accomplish a common goal. However, establishing high data rate, robust, and bi-directional communication links across the air-water interface between aerial and underwater assets is still an open problem. In this article, we propose a communication system based on visible (blue) light that enables aerial and underwater assets to establish bi-directional links through the air-water interface without requiring any preexisting communication infrastructure such as buoys acting as relay nodes. We first derive a mathematical model and accordingly build a simulator for the bi-directional air-water visible light communication (VLC) channel accounting for water surface distribution, optical parameters and path losses. Then, we design and prototype a software-defined visible light communication (VLC) modem. We present an extensive experimental evaluation conducted both in a test tank and in the ocean using the proposed VLC modem prototypes.