This paper introduces a one-way ranging and time-alignment method for distributed multi-mode underwater communication networks that utilize both acoustic and optical front-ends. By capitalizing on the differences in propagation velocities between the optical and acoustic waveforms, the method enables precise distance and timing measurements between any two nodes by analyzing the time differences in signal arrivals. The theoretical foundation of the proposed technique is validated using the Cramer-Rao lower bound (CRLB), which serves as a performance benchmark. The method’s effectiveness is assessed through simulations and experimentally validated in a realistic underwater environment. The results demonstrate that the approach achieves excellent timing alignment with nanosecond precision and ranging accuracy at the centimeter level, utilizing only a single reference transmission. The results significantly enhance the reliability and efficiency of underwater communication systems, paving the way for advanced applications in marine exploration, environmental monitoring, and underwater robotics.

This paper presents a proof-of-concept for the UniSDM architecture, which is capable of simultaneously operating across acoustic, optical, magnetic induction, and RF communication modes. A flexible firmware stack is developed that integrates the logic for modem operation and supports multiple underwater communication modes mentioned above and the protocols and standards such as OFDM and JANUS for acoustics, as well as OFDM, single carrier, and IRDA-like protocols for optical communication. Additionally, it provides various interfaces, including a socket-based API, Ethernet tun-neling, and a graphical user interface (GUI). The firmware architecture incorporates cross-layer frame and waveform processing, enabling advanced communication paradigms such as multimode cooperative MIMO.

In this paper, a Universal Underwater Software Defined Modem (UniSDM) architecture is proposed that may operate in different modes (acoustic, magnetic induction, optical and RF), in order to utilize the advantages of each mode and accordingly satisfy the requirements of many latest use cases in underwater communication systems. A detailed description of the novel UniSDM architecture is presented first. The novelty of this architecture is its flexibility, i.e., allowing the designers to produce a device that may include any type of modes operating seamlessly and jointly by exchanging data, control and synchronization. Many challenges, including high system costs and coordination between different modes, are addressed in the paper. Moreover, numerical evaluation is conducted to assess the performance of the proposed UniSDM architecture. Finally, the performance evaluation shows that the utilization of the UniSDM allows to decrease the transmission latency and improve the energy efficiency, while maintaining high reliability and robustness in underwater communication systems.

In recent years, many underwater communication applications have been proposed and tested, leading to the Internet of underwater things (IoUT) concept. In the IoUT, sensors may be deployed individually on sea surface and seabed as well as in water at different depths. They also may be integrated into underwater items such as fish, plants, autonomous underwater vehicles (AUVs), remotely operated underwater vehicles (ROVs), and divers. Depending on the application, different connectivity requirements must be satisfied such as data rate, latency, and reliability. However, the underwater communication channels pose a significant challenge to meet these requirements. To accommodate various applications with different service level agreements (SLAs), a multimode (acoustic, optical, and magnetic induction (MI)) communication system is proposed to take advantage of the modes' complementary features. Furthermore, an automatic network slicing (ANS) solution is proposed to provide globally optimized resource management, enhanced quality of service (QoS), simplified network operation, reduced deployment cost, and functional isolation of services. Taking the channel characteristics of the acoustic, optical, and MI communication modes into consideration, an optimization problem is formulated and solved for multimode IoUT (MM-IoUT) to enable admission control, routing, and dynamic resource allocation based on the different SLAs. Numerical analysis is conducted to verify the proposed solution and evaluate its performance.

In this paper we propose a woven block code construction based on two convolutional outer codes and a single inner code. We proved lower and upper bounds on this construction's code distance. The lower bound is shown to be higher than the product of the free distances of inner and outer constituent codes. Since this construction uses well-developed convolutional constituent codes, we believe that it would be competitive to turbo codes in the future mobile communication systems.

In this paper we propose to consider a generalized error-locating code (GEL-code) as a possible candidate for data transmission systems that require high code rates along with strict requirements on wrong decoding probability. GEL codes are one of a few that allow analytical computation of code error probability bounds and have practical construction method. The paper describes the construction of the GEL-code and the algorithms for encoding and decoding. It represents the upper and lower bounds on wrong decoding probability. It gives a method for constructing such GEL code (with the minimal redundancy) that guarantees that the probability of wrong decoding will be less than required one (for a given channel error probability). Numerical results for the upper and lower bounds for the various GEL-codes and the analysis of the energy gain for the different signal-code structures are given.