[Show abstract][Hide abstract] ABSTRACT: Simulation and experimentation of underwater networks entail many challenges, which for the former are mainly related to the accurate modeling of the channel behavior, while they are typically logistic in nature for the latter. In this article, we present our experience with WOSS and DESERT Underwater, two open source suites address both classes of challenges. The suites build on and extend the capabilities of ns2 and NS-MIRACLE, two widely known software packages for network simulation. WOSS endows NS-MIRACLE with the capability to generate realistic channel patterns by automatically retrieving and processing the environmental boundary conditions that influence such patterns; DESERT Underwater makes it possible to evolve toward at-sea experiments by reusing the same code written for simulations, thereby minimizing the effort required for network deployment and control. Both suites have been widely tested and used in several projects: some examples are provided in this respect, including an account of some experiments carried out in collaboration with the NATO STO Centre for Maritime Research and Experimentation.
[Show abstract][Hide abstract] ABSTRACT: This paper presents ALBA-R, a protocol for convergecasting in wireless sensor networks. ALBA-R features the cross-layer integration of geographic routing with contention-based MAC for relay selection and load balancing (ALBA), as well as a mechanism to detect and route around connectivity holes (Rainbow). ALBA and Rainbow (ALBA-R) together solve the problem of routing around a dead end without overhead-intensive techniques such as graph planarization and face routing. The protocol is localized and distributed, and adapts efficiently to varying traffic and node deployments. Through extensive ns2-based simulations, we show that ALBA-R significantly outperforms other convergecasting protocols and solutions for dealing with connectivity holes, especially in critical traffic conditions and low-density networks. The performance of ALBA-R is also evaluated through experiments in an outdoor testbed of TinyOS motes. Our results show that ALBA-R is an energy-efficient protocol that achieves remarkable performance in terms of packet delivery ratio and end-to-end latency in different scenarios, thus being suitable for real network deployments.
IEEE Transactions on Parallel and Distributed Systems 03/2014; 25(3):529-539. · 2.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we discuss the performance of different network protocols for RACUN, a European Defence Agency project with the objective of demonstrating ad hoc underwater networks for multiple purposes related to security. The RACUN network is designed for long-range communications over areas of large size, hence a very important role is played by the network protocols employed. We show that the channel realizations observed in typical scenarios and the physical layer schemes available in the project lead to significant bit error rates. Therefore, the protocols that offer some inherent form of redundancy, as in the case of flooding-based protocols, tend to yield better performance than protocols based on the exchange of signaling traffic. In support of this statement, we simulate two scenarios for the RACUN network over channel realizations that are statistically derived from real channel measurements. Our results provide insight on the advantages and drawbacks of the different packet forwarding strategies, and confirm that flooding-based approaches perform better. In addition, we prove how splitting packets into multiple fragments to match the modem's maximum service data unit significantly limits the performance.
Proceedings of the Eighth ACM International Conference on Underwater Networks and Systems; 11/2013
[Show abstract][Hide abstract] ABSTRACT: In this paper, we introduce Underwater Selective Repeat (USR), a Selective Repeat Automatic Repeat reQuest (SR-ARQ) mechanism for multiuser underwater acoustic networks. Our scheme exploits the typically large round-trip time (RTT) of underwater acoustic links to interlace the transmission of data and acknowledgment (ACK) packets, such that the transmitter never starts sending data packets when it should receive ACKs. No specific synchronization mechanism is required to do so. It is shown that the timing of point-to-point communications can be adjusted to optimize the performance of multiuser networks of a given size. Moreover, it is shown that the proposed strategy can be made robust to mobility, hence to time-varying RTTs. We provide detailed simulation results that assess the performance of USR as a function of the protocol parameters, both in static and in mobile networks. Based on these results, we propose an adaptive version of USR, whereby a node can modify its behavior (e.g., it can pack data transmissions more tightly or more loosely within one RTT) by reacting to packet errors induced by multiple-access interference.
[Show abstract][Hide abstract] ABSTRACT: We propose a theoretical framework to evaluate the expected throughput of underwater networks over an ensemble of node topologies and propagation environments. The analysis is based on the assumptions that the transmitters are spatially distributed according to a Poisson point process, and that the channel follows a Rayleigh fading distribution, with a mean that is determined by spreading loss and frequency-dependent absorption. We evaluate the probability of a successful transmission, i.e., the probability that the signal-to-interference-and-noise ratio at the typical receiver is greater than a given threshold, and determine the maximum network throughput density over the transmitter density and the operating frequency. The theoretical results are validated using a realistic underwater channel simulator based on ray tracing. It is demonstrated that, for a number of practical scenarios, the theoretical and simulated throughput match provided that the spreading-loss exponent is appropriately fitted to the simulation scenario. Overall, the proposed framework provides easy-to-obtain network throughput results, which can be used as a complement or an alternative to time-costly, deployment-dependent network simulations.
[Show abstract][Hide abstract] ABSTRACT: The recent development of underwater acoustic modems has enabled multihop networking capabilities that can be used in important military and civilian applications. For this reason, routing protocols for underwater acoustic networks (UANs) have recently been proposed and evaluated. However, the interactions between channel dynamics and networking performance are not well understood. In this paper, we investigate and quantify the effect of the time-varying (TV) link quality on routing protocols in static UANs. In order to do so, we simulate the considered routing protocols in several network scenarios, obtained by changing the network density, the number of packet retransmissions, the packet length, the modulation type, and the power level with both TV and time-invariant (TI) channel conditions. Results confirm that, when evaluating the performance of routing protocols, it is important to understand the TV behavior of the channel quality over intervals of time sufficiently long to accommodate multihop communications. Finally, we also present experimental results, confirming the outcome of the simulations. The experiments have been conducted in collaboration with the NATO Centre for Maritime Research and Experimentation (CMRE) during the CommsNet12 sea trial.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we consider a coastal surveillance scenario, where Autonomous Underwater Vehicles (AUVs) patrol an area of interest and inspect surface ships or underwater assets passing through the area. A shore-based control center monitors the AUVs by means of delay-tolerant networking techniques. In particular, as the AUVs carry out their patrolling task, they may get in contact with one another and have a chance to exchange data about the inspected assets (identity, route followed, movement speed, etc.). Given that the area to be patrolled is usually quite large, these contacts are erratic and time-limited: this makes the AUVs and the sink a Delay-Tolerant Network (DTN). To make the communication between AUVs more effective during a contact, we propose a DTN protocol which splits the estimated contact duration between the nodes involve and enhance this protocol using an Automatic Repeat reQuest (ARQ) technique based on selective repeat for error control. Moreover, the structure of the signaling packets exchanged prior to data transmission is designed to help estimate the contact duration and thereby optimize the subsequent data packet exchange. Simulation results demonstrate that the proposed protocol outperforms other ARQ-based DTN routing protocols.
[Show abstract][Hide abstract] ABSTRACT: DESERT Underwater (short for DEsign, Simulate, Emulate and Realize Test-beds for Underwater network protocols) is a complete set of public C/C++ libraries to support the design and implementation of underwater network protocols. Its creation stems from the will to push the studies on underwater networking beyond simulations. Implementing research solutions on actual devices, in fact, is of key importance to realize a communication and networking architecture that allows heterogeneous nodes to communicate reliably in the underwater environment. In this paper, we first discuss the rationale behind this work, and, then we list and briefly describe all the DESERT Underwater libraries currently implemented. In line with the current trends in underwater networking, our approach makes it possible to reuse the same code prepared for simulations in order to realize underwater network prototypes. We also present some preliminary tests that confirm the feasibility of the proposed solution for the design and evaluation of underwater network protocols. In this perspective, we believe that DESERT Underwater is a useful tool to profitably develop and test real world applications.
[Show abstract][Hide abstract] ABSTRACT: The quest for sustainable energy models is the main factor driving research on smart grid technology. SGs represent the bridging paradigm to enable highly efficient energy production, transport, and consumption along the whole chain, from the source to the user. Although this concept promises to be very fruitful, the research on how to deploy it in the real world has just begun. A discussion on the enabling technologies for SGs and a possible roadmap for the profitable evolution thereof is the focus of this article. After introducing the recent trends that are pushing the SG paradigm, we will discuss various key scenarios for the SG, and briefly introduce some of its key requirements. We will then provide an analysis of how current and future standard solutions in the areas of communications and networking can be engineered into a system that fulfills the needs of the SG vision. We advocate the use of small, cheap, and resource-constrained devices with pervasive computing capabilities as the key component to deploy a ubiquitous energy control system. To this end, the recent efforts carried out by Internet standardization bodies such as the IETF and W3C toward the vision of the Internet of Things (IoT) are especially relevant. The various components of the proposed solution have been successfully showcased in real-world implementations, and relevant actors such as ETSI, ZigBee, and IPSO are already evaluating their potential for future IoT applications, making the Internet-based smart grid vision considered in this article practically achievable in the not too distant future.
[Show abstract][Hide abstract] ABSTRACT: Channel variability and a high level of noise lead to a significant probability of packet loss in many underwater networks. Techniques based on packet-level Forward Error Correction (FEC), such as Reed Solomon (RS) codes, can be used to offer effective protection against excessive packet losses that would be generated by noise. In this paper, we propose a new error recovery scheme based on RS codes to be used in conjunction with multipath routing. We discuss several routing policies to take advantage of the inherent redundancy of multi-path routing coupled with a suitable RS code. We evaluate the performance of these policies through simulation and compare them with the Multi-Sink Routing Protocol (MSRP). Results show that our policies outperform MSRP in terms of packet delivery ratio (PDR), and that our solution strikes a balance between the achieved PDR and the overhead introduced by packet replication.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we consider data uploading from a network of fixed sensors to a mobile Autonomous Underwater Vehicle (AUV). We approach the problem using both random and controlled access: in particular, we propose UW-Polling, a data retrieval protocol based on controlled access, and evaluate it against channel access protocols based on random access. We compare the performance of these protocols in terms of throughput, Packet Delivery Ratio and energy consumption, discussing the impact of the source power level on these metrics. Our results show that our polling-based protocol outperforms the other protocols in several cases, and thereby confirm that polling is an effective approach to enable AUVs to retrieve data from a network of fixed sensors.
[Show abstract][Hide abstract] ABSTRACT: We consider an underwater networking scenario, and test the performance of two multihop routing paradigms, source routing and hop-by-hop relay selection, in the presence of different representations of the channel dynamics. We focus on a static channel case (obtained via empirical equations for path-loss), and on a sequence of channel realizations obtained using ray tracing, that vary both slowly and rapidly over time with respect to the expected reaction time of routing protocols; the two latter cases are also explored in the presence both of a flat bottom and of a rough bottom with several seamounts, to yield a total of five different channel models. Our results show that channel variations induced by environmental changes over time have an impact on routing performance metrics in connected topologies. A sea bottom with a rough shape adds a further impact to the routing performance, which is shown to be larger for source routing. We conclude that while empirical channel models yield a good first-order approximation, the time-variability of the channel and the shape of the network area boundaries are to be taken into account in order to achieve more realistic network performance estimates.
Signals, Systems and Computers (ASILOMAR), 2012 Conference Record of the Forty Sixth Asilomar Conference on; 01/2012
[Show abstract][Hide abstract] ABSTRACT: In this paper we present a performance evaluation and feasibility test of SUN, a routing protocol for underwater networks inspired to Dynamic Source Routing (DSR), to which it adds several features that improve its behavior in underwater environments. The evaluation has been performed with real devices, and has been made possible through a collaboration between the Department of Information Engineering (DEI) of the University of Padova, Italy and EvoLogics GmbH, Germany. In detail, the idea put in practice in this work is to command real hardware, i.e., the S2C acoustic modems of EvoLogics, by means of the ns2/NS-Miracle engine developed and extensively used primarily by research institutions. This approach favors code reuse and speeds up the realization of flexible and easily modifiable network prototypes. Our results show that SUN can deal with typical network issues such as the disconnection of a node and the appearance of additional nodes, and that it copes well with dynamic topology changes.
[Show abstract][Hide abstract] ABSTRACT: One of the challenges faced by future networks is to integrate heterogeneous segments whose protocols are optimized for very different conditions. This work provides an overview of project COMPOUND, which tackles problems in this class to interface an underwater acoustic network comprising both static and mobile nodes to the Internet. The main goal is to create value and foster new applications in a niche but strategically important area by making the data and assets in the network easily available to a wide community. This will reduce the time, effort, and cost needed to customize the network to suit a specific need. A key insight in COMPOUND is to extensively exploit knowledge of node positions, including submerged ones with no access to GPS, to configure the network parameters at multiple levels, from the Internet gateway down to a node's physical layer. In turn, positioning is derived from observed data traffic on the network and collaborative exchanges between nodes, resulting in a system that tightly integrates positioning and communications. This paper discusses the proposed approach within the scope of current research on underwater acoustic communications and networking, describes application scenarios, envisaged technical solutions, planned developments, and identifies some of the possible impacts of this work.
Future Network & Mobile Summit (FutureNetw), 2012; 01/2012
[Show abstract][Hide abstract] ABSTRACT: In this paper, we consider underwater network prototyping using the network simulation engine NS-Miracle, and investigate different embedded computer boards that can be employed for this task. In particular, we consider two embedded platforms with considerably different capabilities: the PandaBoard (a powerful platform that does not require any cross-compilation effort) and version 5.2 of the NetDCU board, which is much more constrained in terms of computational power, RAM and storage space. After describing the steps required to install NS-Miracle and the DESERT Underwater libraries on board these platforms, we report on the field experiments conducted to test the corresponding prototypes. Our results include a comparison between the two investigated platforms in terms of resources required (e.g., memory occupancy and energy expenditure) and performance in the execution of real-time software (e.g., delays introduced within the simulation framework). We believe that our work represents an interesting step towards the realization of underwater network prototypes made of heterogeneous nodes.
[Show abstract][Hide abstract] ABSTRACT: Recent simulation software such as WOSS  and similar packages make it possible to perform accurate simulations of underwater acoustic networks by taking into account the actual behavior of sound propagation. In this paper, we focus on deep-water acoustic networks, and employ WOSS to compare the performance of three MAC protocols based on random access. The final goal of this effort is to test several network scenarios and baseline protocol approaches, and to understand which is more likely to offer top performance in underwater networks. In fact, it is still a partly open question whether or not there is a medium access control (MAC) protocol that is "good" in most if not all scenarios and network arrangements; or, at least, if any MAC protocol would be able to emerge as the de facto choice for most applications and network topologies. In this paper, we perform a comparison of MAC protocols in deep-water scenarios, in order to extend previous analyses, which targeted mainly shallow water networks. We will consider three types of medium access control: random access with instantaneous carrier sensing , transmitter-side tone-driven contention , and 3-way Request-To-Send/Clear-To-Send (RTS/CTS)-based access .