Joao Alves

Symmetric cryptography is the de-facto approach to information security for ad-hoc underwater acoustic networks. The requirement is that all network nodes possess the same cryptographic keys and key distribution that happens offline. Thus, it is hardly possible to include a new keyless node during network operation. In addition, online key replenishment is an open problem. In this article, we tackle key distribution/replenishment by formulating a new protocol that generates a key between two trusted underwater acoustic nodes (Alice and Bob) without the need to exchange the key itself. The proposed protocol initially extracts common acoustic channel features between Alice and Bob after some signal exchanges. Then, each party uses these features to generate his/her own secret bits via a random sequence generator. To correct any differences in their secret bits, we propose two reconciliation methods that employ Reed–Solomon codes. At the last step of the protocol, a 256-bit cryptographic key is generated by feeding the reconciled secret bit string to the Secure Hash Algorithm 3. We evaluate the key generation rate of the proposed protocol with real acoustic data recorded from a littoral environment, in which Alice and Bob exchanged 915 channel probes over different link geometries. To assess security performance, we invent a passive eavesdropper, Eve, who is able to simulate the acoustic link between Alice and Bob. She uses her simulated channels and the same protocol to generate her keys. Our analysis demonstrates a tradeoff between the key generation rate of Alice and Bob and Eve's ability to extract the same key. Our best result shows that Alice and Bob can independently generate 567 keys out of 915 attempts while Eve does not have access to any of the keys.

As the Arctic Ocean becomes increasingly accessible due to the continuous sea-ice retreat during the last decades, UnderWater Acoustic (UWA) communications will play a pivotal role in future underwater Arctic exploration/exploitation activities that will inevitably emerge. In this paper, we aim to improve the reliability of short packet transmission typically needed for low-latency low-packet-loss communications. In particular, we compare the Packet Error Rates (PERs) of convolutional, turbo, Low-Density Parity-Check (LDPC) and polar codes. These four codes are implemented in the physical layer of a software modem, which uses single-carrier, Binary Phase Shift Keying (BPSK) modulation achieving 360 bits/s over the 3830-6170 Hz band. The modem transmitted 128-, 256-, 384-bit long packets over various UWA links north-west off the Svalbard Islands in June 2021. The packets were recorded in a linear hydrophone array and our offline analysis shows that there is an enormous reduction in the PER for all codes as the number of the used hydrophones increases from one to four. In addition, our results confirm the superiority of the polar code for all packet lengths and number of hydrophones.

Abstract Underwater acoustic communications are currently implemented through a variety of vendor-specific protocols. The lack of interoperability between these protocols has prompted the North Atlantic Treaty Organization (NATO) Science and Technology Organization (STO) Centre for Maritime Research and Experimentation (CMRE) to lead a collaborative effort toward the establishment of a standard for digital underwater acoustic communications. The JANUS standard was promulgated as a NATO standard, Standardization Agreement (STANAG) 4748, in March 2017 and has since been used by a growing number of vendors.To promote interoperability and engagement with industry, CMRE began organizing the JANUS Interoperability Fest. The goal of this event was to collectively exercise JANUS implementations from companies and to clear up any possible misunderstandings with the technical specification. The first edition of the JANUS Fest took place in 2018. This article describes the planned and performed tests as well as the primary outcomes of the second JANUS Fest, which was organized in 2019. The success of this event is demonstrated by the results and the positive feedback from participants and observers.

In stark contrast to a typical underwater acoustic network (UAN) deployed in mid-latitudes, ice-covered environments make network deployment difficult and expensive. A limited number of nodes must cover ranges of hundreds of kilometers. We tackle the network design in three layers: engineering, physical, and networking. At the engineering layer, we investigate hardware and bandwidth limitations for real-world implementation. Based on the proposed bandwidth, we design a software modem equipped with three waveforms achieving 1.8, 21.4, and 96.2 b/s. The packet error rate performance is computed with a channel simulator that takes realistic environmental parameters. Our simulations show that ranges of more than 100 km can be achieved in two High North areas during summer months provided that the point-to-point links exploit the ducted sound propagation. However, during winter months, this performance may not be always possible and multiple hops may be needed to cover the same range. Finally, based on the outcomes of the physical layer, an adaptive cross-layer routing protocol, termed network-aware adaptive routing (NADIR), is simulated. Link quality, energy consumption, and topological data are used to select the best coded modulation scheme and relay node in the next transmission slot. Our results show that the use of an adaptive strategy offers higher packet delivery and lower energy consumption than a nonadaptive strategy.

Increasing the operational safety of Autonomous Underwater Vehicles (AUVs) is necessary to fully explore their potential. Currently, AUV operations are limited by several constrains including the need to guarantee no interference with manned vessels and a safe deployment and recovery. Exclusion zones are used in many deployments to de-conflict activities but in a near-future world, populated by manned and unmanned surface and underwater vehicles, this will not be enough. In the absence of clear rules and ideal perception capabilities, one way to prevent collisions is to use acoustic communications. In this article, we propose several ways of improving the safety of AUVs and manned vehicles operations through the use of JANUS, the first standard for underwater digital communications. Other ways to communicate underwater could be explored but the usage of a standard protocol represents a landmark step to implement collision avoidance rules and to make the operations of heterogeneous AUVs safer.

Unmanned Surface Vehicles (USVs) are a widespread technology nowadays. USVs of all kinds and shapes are used for a variety of applications from scientific research to transportation. However, safety and regulatory issues still prevent the exploitation of the full potential of USVs. In particular, without a well-defined safety standard and efficient risk allocation, it is hard to assign liability and define insurance or compensation schemes. In this article, we will discuss different types of liability regimes that could be applied to different types of USVs classified by length and autonomy level.

This paper presents an overview of the functionalities of the Cognitive Communications Architecture (CCA) that is currently under development at the NATO Science and Technology Organisation (STO) Centre for Maritime Research and Experimentation (CMRE). The CCA is designed to enable the deployment of advanced autonomous underwater solutions making use of smart, adaptive and secure underwater networking strategies. The CCA and the implemented network modules have been extensively tested, validated and improved during various at-sea campaigns conducted in recent years, involving CMRE and partners. The collected results show that the CCA is a robust, reliable and effective solution supporting underwater communications and networking. It provides various functions and services for the development of novel cognitive and secure communication strategies, such as a cross-layer networking functionality and the ability to easily integrate various existing communications technologies. These aspects are key enablers in the construction of a system that is robust to challenging conditions, such as those posed by varying channel conditions or adversarial attacks.