Daniele Spaccini

CARP: A Channel-aware routing protocol for underwater acoustic wireless networks

The paper concerns the definition and performance evaluation of a new multi-hop routing protocol for underwater wireless sensor networks. Our solution, termed CARP for Channel-aware Routing Protocol, exploits link quality information for data forwarding, in that nodes are selected as relays if they exhibit recent history of successful transmissions to their neighbors. CARP avoids loops and can successfully route around connectivity voids and shadow zones by using simple topology information, such as hop count. The protocol is also designed to take advantage of power control for selecting robust links. The performance of CARP has been compared with that of two other protocols for underwater routing, namely, the Focused Beam Routing (FBR) and a flooding-based solution (EFlood). Metrics of interest include packet delivery ratio, end-to-end packet latency and energy consumption, which have been investigated through ns2-based simulations and experiments at sea. The in-field trials have been conducted at two European locations, namely, a Norwegian fjord and the Mediterranean Sea. The tests in the Mediterranean Sea have been performed jointly with the NATO Science and Technology Organization Centre for Maritime Research and Experimentation (STO CMRE), under a collaboration agreement between the University of Roma and CMRE. 1 Our results show that CARP robust mechanism for relay selection doubles the packet delivery

The SUNSET framework for simulation, emulation and at-sea testing of underwater wireless sensor networks

The Sapienza University Networking framework for underwater Simulation Emulation and real-life Testing (SUNSET) is a toolkit for the implementation and testing of protocols for underwater sensor networks. SUNSET enables a radical new way of performing experimental research on underwater communications. It allows protocol designers and implementors to easily realize their solutions and to evaluate their performance through simulation, in-lab emulation and trials at sea in a direct and transparent way, and independently of specific underwater hardware platforms. SUNSET provides a complete toolchain of pre-deployment and deployment time tools able to identify risks, malfunctioning and under-performing solutions before incurring the expense of going to sea. Novel underwater systems can therefore be rapidly and easily investigated. Heterogeneous underwater communication technologies from different vendors can be used, allowing the evaluation of the impact of different combinations of hardware and software on the overall system performance. Using SUNSET, underwater devices can be reconfigured and controlled remotely in real time, using acoustic links. This allows the performance investigation of underwater systems under different settings and configurations and significantly reduces the cost and complexity of at-sea trials. This paper describes the architectural concept of SUNSET and presents some exemplary results of its use in the field. The SUNSET framework has been extensively validated during more than fifteen at-sea experimental campaigns in the past four years. Several of these have been conducted jointly with the NATO STO Centre for Maritime Research and Experimentation (CMRE) under a collaboration between the University of Rome and CMRE.

SUNSET version 2.0: enhanced framework for simulation, emulation and real-life testing of underwater wireless sensor networks

We describe the newest design and development of the Sapienza University Networking framework for underwater Simulation Emulation and real-life Testing (SUNSET), a powerful toolkit for implementation and testing of novel protocol solutions for underwater sensor networks. SUNSET enables testing and enhancement of underwater solutions using a controlled simulation environment. The very simulation code can be then transparently ported to various real hardware and underwater platforms for protocol emulation and actual in field testing. SUNSET was the first open source framework for seamless simulation, emulation and actual at sea testing of novel underwater systems. The first SUNSET was presented in 2011 [1], improved in 2012 [2] and freely released to the research community in May 2012. Since then, SUNSET has been significantly improved and validated through several trials at sea. New modules have been created and the functionalities of existing ones have been extended and enhanced. The new SUNSET version 2.0 has been recently released to the community (October 2013 [3]). This paper discusses in details the SUNSET 2.0 features and modules, and report about the latest in field tests where SUNSET 2.0 has been used.

Investigation of Underwater Acoustic Networking Enabling the Cooperative Operation of Multiple Heterogeneous Vehicles

In this paper, the authors investigate the creation of an underwater acoustic network to support marine operations based on static and mobile nodes. Each underwater device combines communication, networking, and sensing capabilities and cooperates with the other devices in coordinated missions. The proposed system is built upon the SUNSET framework, providing acoustic communications and networking capabilities to autonomous underwater vehicles, autonomous surface vessels, and moored systems, using underwater acoustic modems. Specific solutions have been developed and tested to control the underwater nodes acoustically and to instruct the vehicles on keeping a given formation using acoustic links. One of the novelties of our approach has been the development and utilization of a realistic simulation infrastructure to provide a very accurate representation of all the dynamic systems involved in the network, modeling the vehicle dynamics, the acoustic channel, and the communication messages. This infrastructure has been extensively used to investigate and validate the proposed solutions under different environmental conditions before the actual deployment of devices. Several experiments were then conducted in the laboratory and in the field. The experimental results have confirmed the effectiveness of the proposed solutions and the reliability of the proposed simulation framework in estimating system performance.

Implementation of an underwater acoustic network using multiple heterogeneous vehicles

In this paper we investigate the creation of an heterogeneous underwater network with static and mobile assets cooperating together in coordinated missions using acoustic links. Each underwater device combines communication, networking, and sensing capabilities, and cooperates with the other devices to accomplish a given task. The flexibility and capability of the proposed system allows to overcome the limitations of commercial solutions currently available in the market which typically focus on point to point communications. SUNSET framework has been used to provide acoustic communication and networking capabilities to AUVs, ASVs and moored systems developed by the Oceans Systems Group, at the University of Porto, in Portugal. New solutions have been developed and tested allowing to combine together acoustic data transmission and ranging estimation, to control the underwater nodes acoustically and to instruct the vehicles on keeping a given formation using acoustic links. To validate the proposed approach several experiments with increasing complexity have been conducted at the laboratory and in the field. The experimental results confirm the validity, efficiency and reliability of the proposed solution opening to several possibilities for future developments.

Channel replay-based performance evaluation of protocols for underwater routing

The paper presents a comparative performance evaluation of two routing protocols for underwater wireless sensor networks (UWSNs). The two protocols are the Channel-Aware Routing Protocol (CARP), exemplary of a cross layer approach to underwater routing, and a simple variation of common flooding, called EFlood, where performance is enhanced by introducing random re-transmission times. The scenarios we consider are obtained via simulations and from trials at sea performed under a collaboration agreement between the University of Roma “La Sapienza” and the NATO Science and Technology Organization Centre for Maritime Research and Experimentation (STO CMRE). Two sets of simulations results are shown where the physical layer is modeled by a ray-traced channel as well as by replaying real channel traces, under the same network configuration. Results are also reported from campaigns of experiments at sea. Comparing all results shows how channel replay mimics faithfully actual channel dynamics with respect to what is achievable through a simulated channel model, thus demonstrating the effectiveness of this technique for a fair and repeatable performance comparison of solutions for UWSNs.

A self-adaptive protocol stack for Underwater Wireless Sensor Networks

In this paper we propose the adoption of a self-adaptable cross-layer and modular Software Defined Communication Stack (SDCS) for Underwater Wireless Sensor Networks. The SDCS is a modular stack solution which is capable to run different protocols at each layer of the network stack; a new component, named policy engine, autonomously and adaptively, as the operational conditions vary, selects the protocol of each layer so as to optimize application scenario metrics of interest, e.g., packet delivery ratio, end-to-end packet latency and energy consumption. As a proof of concept, the paper presents the design and performance evaluation of a policy engine to dynamically and autonomously change the MAC protocol adopted in Underwater Wireless Sensor Networks. The best MAC protocol is chosen according to network conditions and application requirements, without any a priori knowledge. We consider three different MAC protocols running in the SDCS: CSMA, T-Lohi and DACAP that represent the class of simple, intermediate and fully negotiated MAC protocols, respectively. The performance of the three protocols are first compared via simulations considering different network conditions, such as traffic load and packet size. Then, we evaluate the ability of our policy engine to dynamically estimate the network changes and then to select accordingly the best MAC protocol without any a priori knowledge. Results show the effectiveness of our solution in that it is always able to quickly find and choose the MAC protocol that optimizes a given metric in a particular scenario by introducing a really limited overhead in the network.

Clock synchronization and ranging estimation for control and cooperation of multiple UUVs

This paper presents the initial implementation of an acoustic synchronization and ranging system to enable the control and cooperation of multiple Unmanned Underwater Vehicles (UUVs). Our solution is based on acoustic clock synchronization and one-way ranging. It requires minimum overhead while providing accurate and quick estimation of the relative distances among underwater nodes. The use of one-way ranging allows to scale up to large teams of UUVs and reduces the energy consumption of localization techniques. Our solution has been implemented in SUNSET, leveraging on the accurate timing information and scheduled transmissions provided by SeaModem acoustic modems. Chip Scale Atomic Clocks have been integrated in the SeaModem to overcome the typical drift of real-time clocks thus enabling accurate one-way ranging estimation during long term missions. The performance of the proposed system have been extensively evaluated in two at-sea campaigns considering different testing scenarios. We have shown that our scheme is able to maintain high ranging accuracy over time without requiring the high overhead and energy consumption of two way ranging techniques. We have also shown that the proposed scheme for acoustic synchronization is very effective in synchronizing real-time and atomic clocks of underwater nodes, whenever needed. Our results confirm that the proposed solution for synchronization and one-way ranging allows to enable the control of multiple UUVs keeping at the bay the overhead in the network and the time needed to estimate relative distances.

A study on channel dynamics representation and its effects on the performance of routing in underwater networks

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.

Long lasting underwater wireless sensors network for water quality monitoring in fish farms

This paper concerns the implementation of an efficient underwater acoustic network suitable for long lasting environmental monitoring in fish farming. Several hardware and software solutions have been designed and implemented to extend the network lifetime and to make the system autonomous and suitable for such an application scenario. The proposed system is composed of different components. The SUNSET Software Defined Communication Stack (SDCS) is used to provide networking capabilities to underwater nodes communicating acoustically through AppliCon SeaModem modems. The Hydrolab Series 5 probes are used to monitor the water quality. Lifetime of underwater nodes is extended through the use of a novel device that allows to harvest energy from underwater water currents via suitable propellers. In addition, novel sleep and wake up mechanisms have been designed and implemented into the underwater nodes to minimize the energy consumption of the system during the idle periods. The performance of the proposed system has been extensively evaluated in field by monitoring the water quality in three fish farming cages located in the Mediterranean Sea, Italy. The system has been connected to the Internet infrastructure allowing the users to easy interact with the underwater system in real-time. Our results confirm that the proposed system is suitable for long term monitoring providing a reliable and robust data collection scheme with an extended network life time.