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1. Taking Wireless Underground: A Comprehensive Summary

   https://doi.org/10.1145/3587934  

   Pal, Amitangshu; Guo, Hongzhi; Yang, Sijung; Akkas, Mustafa Alper; Zhang, Xufeng (March 2023, ACM Transactions on Sensor Networks)

   The tremendous potentials of sensing and communication technologies have been explored and implemented for different remote event monitoring applications over the last two decades. However, the applicability of sensing and communication technologies are not necessarily limited to above-ground environments, but also implementable and applicable for subterranean, underground scenarios. However, as opposed to air medium, underground communication medium is very harsh due to the presence of heterogeneous underground materials along with underground aqueous components. In this paper, we provide a technical overview of different underground wireless communication technologies, namely radio, acoustic, magnetic and visible light, along with their potentials and challenges for several underground applications. We also lay out a detailed comparison among these technologies along with their pros and cons using detailed experimental results. 

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2. Cross-Medium Photoacoustic Communications: Challenges, and State of the Art

   https://doi.org/10.3390/s22114224  

   Mahmud, Muntasir; Islam, Md Shafiqul; Ahmed, Akram; Younis, Mohamed; Choa, Fow-Sen (June 2022, Sensors)

   The current era is notably characterized by the major advances in communication technologies. The increased connectivity has been transformative in terrestrial, space, and undersea applications. Nonetheless, the water medium imposes unique constraints on the signals that can be pursued for establishing wireless links. While numerous studies have been dedicated to tackling the challenges for underwater communication, little attention has been paid to effectively interfacing the underwater networks to remote entities. Particularly it has been conventionally assumed that a surface node will be deployed to act as a relay using acoustic links for underwater nodes and radio links for air-based communication. Yet, such an assumption could be, in fact, a hindrance in practice. The paper discusses alternative means by allowing communication across the air–water interface. Specifically, the optoacoustic effect, also referred to as photoacoustic effect, is being exploited as a means for achieving connectivity between underwater and airborne nodes. The paper provides background, discusses technical challenges, and summarizes progress. Open research problems are also highlighted. 

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3. Enabling Long-Range Underwater Backscatter via Van Atta Acoustic Networks

   https://doi.org/10.1145/3603269.3604814  

   Eid, Aline; Rademacher, Jack; Akbar, Waleed; Wang, Purui; Allam, Ahmed; Adib, Fadel (September 2023, ACM)

   We present the design, implementation, and evaluation of Van Atta Acoustic Backscatter (VAB), a technology that enables long-range, ultra-low-power networking in underwater environments. At the core of VAB is a novel, scalable underwater backscatter architecture that bridges recent advances in RF backscatter (Van Atta architectures) with ultra-low-power underwater acoustic networks. Our design introduces multiple innovations across the networking stack, which enable it to overcome unique challenges that arise from the electro-mechanical properties of underwater backscatter and the challenging nature of low-power underwater acoustic channels. We implemented our design in an end-to-end system, and evaluated it in over 1,500 real-world experimental trials in a river and the ocean. Our evaluation in stationary setups demonstrates that VAB achieves a communication range that exceeds 300m in round trip backscatter across orientations (at BER of 10−3). We compared our design head-to-head with past state-of-the-art systems, demonstrating a 15× improvement in communication range at the same throughput and power. By realizing hundreds of meters of range in underwater backscatter, this paper presents the first practical system capable of coastal monitoring applications. Finally, our evaluation represents the first experimental validation of underwater backscatter in the ocean. 

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4. A Survey on Direct-to-Device Satellite Communications: Advances, Challenges, and Prospects

   https://doi.org/10.1145/3697253.3697265  

   Pasandi, Hannaneh B; Fraire, Juan A; Ratnasamy, Sylvia; Rivano, Herve (November 2024, ACM)

   Direct-to-Device (D2D) communication in satellite networks represents a significant advance in telecommunications, enabling seamless connectivity without relying on terrestrial infrastructure. This survey aims to provide a detailed overview of D2D communication technologies, protocols, applications, and recent advances based on the current state of D2D. We categorize the literature on D2D into a new taxonomy. This taxonomy covers technological foundations, protocols and algorithms, use cases, challenges, and future trends. We emphasize the key challenges and pinpoint research gaps within each category, offering a well-structured domain overview. 

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5. The Underwater Backscatter Channel: Theory, Link Budget, and Experimental Validation

   https://doi.org/10.1145/3570361.3613265  

   Akbar, Waleed; Allam, Ahmed; Adib, Fadel (October 2023, ACM)

   Underwater backscatter is a recent networking technology that enables net-zero-power communication and sensing in underwater environments. Existing research on underwater backscatter has focused on designing and demonstrating early systems with impressive capabilities; however, what remains critically missing is an end-to-end analysis of the underwater backscatter communication channel, which is necessary to understand the potential of this technology to scale to real-world applications and practical deployments. This paper presents the first comprehensive theoretical and empirical analysis of the underwater backscatter channel, including the downlink and uplink of end-to-end backscatter. We introduce a closed-form analytical model that encompasses the physical properties of piezoelectric materials, electromechanical coupling, electrical impedance, and the underwater acoustic channel. We verify the correctness of this theoretical analysis through both finite-element-model physical simulations and real-world experimental validation in a river, demonstrating that the analytical model matches our real-world experiments with a median deviation of only 0.76 dB. Using this model, we then simulate the theoretical limits of underwater backscatter as a function of different design parameters and identify pathways for pushing underwater backscatter toward its theoretical limits. 

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