The LOON in 2014: test bed descriptionJoao Alves, John Potter, Piero Guerrini, Giovanni Zappa, Kevin LePage

NATO STO Centre for Maritime Research and ExperimentationLa Spezia, Italy

{alves,potter,guerrini,zappa,lepage}@cmre.nato.int

Abstract

The interest in underwater communication has grown rapidly in the last few decades, as the ability to deploy assets at seawith increased levels of autonomy naturally led to the problem of getting data to and from them. Despite it’s mature researchtopic status, underwater acoustic communications still faces high barriers when it comes to reaching consensus, not only onthe communication processes but also on modelling and validation methodologies under which to perform objective comparisonof methodologies. Having access to a persistent unattended infrastructure that enables long term testing of physical and logicalunderwater communications processes allows researchers to have access to precious real world data without the full cost of asea trial and with the added bonus of potentially being able to capture variability on the seasonal scale. This paper presentsthe 2014 version of the Littoral Ocean Observatory Network (LOON): a test bed implemented by the NATO STO Centre forMaritime Research and Experimentation (CMRE), envisioned to foster cooperative development of underwater communicationsand networking. The data collection infrastructure provides a comprehensive data set of environmental, acoustic and packetmeasurements relevant to study the the communication processes for the physical and logical layers. This document focuses onthe description of the test bed in its 2014 version, the expected benefits and the opportunities for the underwater communicationsresearch community.

Index Terms

Underwater Communication, Test beds, Acoustics, Sea Trials, Networking, Protocols

I. INTRODUCTION AND SCOPE

Due to the ever-increasing diversity of applications, underwater networking is currently a very active area of research. Whiletheoretical developments are continuously proposed and simulations can be achieved within reasonable levels of commitmentand effort, at-sea testing is very difficult, costly and risky. There is therefore a marked lack of experimental confirmation ofthe expected and theoretical performance of communications protocols, particularly for multiple asset scenarios.

The primarily objective of the deployment of an underwater communications test bed was to enable these research anddevelopment activities at CMRE, by providing an easily accessible test platform deployed just outside the centre’s premisesand available in a permanent way. Such setup would combine the convenience of a tank facility with the ability to explorerelevant inter-node distances in real world environments.

The idea to develop a proof-of-concept, always available and remotely accessible underwater networking test bed is not new.Perhaps the best known example is the Seaweb project [1], under which a test bed for development of underwater communicationprotocols was developed [2]. This was not intended to be an open test bed to serve the underwater communications communitybut rather a prototyping and testing platform for Seaweb.

In June 2011, in support for its programme of work, CMRE deployed for the first time its underwater network in the bayof La Spezia to be used as a communications test bed. The deployment of 2011 is presented in [3]. In 2012 and 2013 thetest bed was expanded and re-located to the coastal area West of the Palmaria Island. In 2014, and in order to increase theavailability of the system (by decreasing the risks to the equipment and reduce the time required for technical interventions),the LOON was again deployed inside the harbour area of La Spezia in early March 2014.

II. PREVIOUS DEPLOYMENTS

The AcommsNet11 trial, started in June 2011, marked the first deployment of the LOON. This deployment allowed to stress-test in-house hardware and software developments like the acoustic acquisition system and the networking communication suite,further test the DTN adaptation for the underwater domain [4], improve CMRE’s routing solutions [5], further expand JANUSapplications and networking [6] and test a selective ARQ implementation along the lines of the one presented in [7] withthe added flexibility of enabling adaptive parametrization and to be used either on a typical layer 2 implementation or as adedicated underwater transport layer. Additional testing targeting developments in the fields of cooperative underwater roboticswere made using the test bed. The ranging capabilities of the modems have been explored in order to develop schemes thatallow AUV formation keeping using ranging information as the only positional awareness regarding neighbour vehicles [8].From the outset this capability captured the interest of several institutions that worked with CMRE on data collection andalgorithm developments. The institutions that took part in ACommsNet11, using the underwater communications test bed areFFI (Norway) that performed channel analysis, the University of Rome La Sapienza (Italy) working with CMRE on networking

topics (MAC and routing), the University of Porto (Portugal) with whom CMRE develops the DTN concepts for underwaterapplications and Teledyne Benthos (USA), active on the development of the JANUS physical layer protocol standard [9].

In June 2012, under the scope of the CommsNet12 experiment, the LOON test bed was re-located into the coastal watersof the Ligurian Sea, west of the Palmaria Island. This environment provided a different environmental setup of slightly deepercoastal environment. The experimental programme prepared for CommsNet12 consisted on a series of tests focused on themaritime communications developments ongoing at CMRE. Such developments included underwater routing experiments,delay and disruption tolerant networking, localization techniques for underwater networks, hardware developments for fixedand mobile gateways and proofs of concept in linking separate communication clusters. different solutions were supported ondifferent software frameworks ranging from MOOS-based [10], Uni. of Padova’s DESERT [11] and Uni. of Rome’s SUNSET[12]. The collaborative participants in CommsNet12 included (besides CMRE) the University of Padova (Italy), University ofPorto, Univ. of Rome La Sapienza, GraalTech (Italy) and the modem manufacturer Evologics.

In 2013 the LOON was used for the CommsNet13 experiment in the same location of the previous year. The LOON wasintensely used as a baseline constellation for development and testing of underwater localization solutions and also for networklayer protocol testing. During CommsNet13 the LOON provided 4 of a total of 12 nodes deployed for protocol experimentation.The collaborators that took part in this experimental activity were the Univ. of Rome La Sapienza, Evologics, the Univ. ofPadova and two teams from the Univ. of Florence (Italy) and Univ. of Pisa (Italy) both part of ISME - the inter-universityresearch centre on Integrated Systems for the Marine Environment.

III. TESTBED DESCRIPTION

As previously mentioned, for the 2014 deployment of the LOON the chosen location was again the Gulf of La Spezia.The harbour environment offered by the Gulf, like all other harbours, is far from ideal from a communications standpoint.Commercial shipping introduces high levels of noise that allied to the very shallow water configuration (10m or less), provide achallenging communications channel. The geographic location of the deployment was mainly determined by logistic constraintssuch as ease of access, cable lengths and anchor points for big ships. Figure 1 shows the location of the assets in the Gulf.

Fig. 1. Geographic configuration of the test bed where M1 to M4 are the modem tripods, C is the shore side container lab where the control station islocated, TC is the thermistor chain, H is the hydrophone array and A is the ADCP.

A. System Description

The LOON was envisioned to be modular so that additional equipment of different kinds could be plugged and used asa part of of the test bed. For this to be achieved the simplest electrical and data interfaces were specified. This way anyequipment that can be powered by 24 VDC and exchange data via TCP/IP can potentially be added to the LOON and expandits functionalities beyond the realm of underwater communications. The system implemented and deployed is pictured in Fig2 and can be divided in four main blocks:

• The Communication nodes: Four tripods that are fitted with different commercial, off-the-shelf (COTS) acoustic modems.These nodes are also capable of in-band raw acoustic data acquisition and in one of those there is the capability ofarbitrary waveform generation;

• A separate high definition acoustic data acquisition system composed by an hydrophone array and a 24 bit, 192 kHzacquisition system;

• The support instrumentation including an Acoustic Doppler Current profiler (ADCP) and thermistor chain (TC);• The command system: responsible to interface the sub-systems, run automated experiments, archive collected data and

run self-diagnosis routines. It is installed inside a container lab, on a pier.

Fig. 2. Simplified LOON layout diagram Fig. 3. LOON node diagram

The tripods are cabled in a star topology where one receives AC power and Ethernet from shore and acts as a hub forthe remaining ones. The additional electronics in the tripods include power distribution and management, Ethernet extendermodules and ARM-based processing units.

A tetrahedral array of hydrophones provides full band acoustic raw data at 192 kS/s with 24 bit resolution via an in-housedeveloped acquisition system with continuous full band streaming capability, cabled to shore via optical fibre.

Oceanographic variables are available through in-situ instrumentation: A bottom-mounted, upward looking Acoustic DopplerCurrent Profiler (ADCP) configured to measure surface wave spectra and a thermistor chain to continuously sample thetemperature profile. Both are cabled to shore with independent serial lines and powered by a DC source. The commandsystem, is built around a Linux workstation and serves as the entry point in the test bed. It interfaces and manages directly allthe sub-systems which significantly simplifies the synchronization and time stamping of the acquired samples. The electricalsupport includes IP-controllable power outlets that allow for individual components to be power-cycled in case of anomaly.System diagnosis routines were implemented to guarantee data integrity and archiving both in a local Network Attached Storage(NAS) device and in CMRE servers. Continuous automated monitoring of the individual components allowed for error alertsand daily reports to be sent by email to the system administrators. The command system is intended to be accessible bycredited people following an established procedure. The dry-end equipment was installed in a shore-side container lab. withair conditioning and Uninterrupted Power Supply (UPS). The complete layout required a total of around 4 km of underwatercable deployed in the sea floor of the Gulf.

Since a part of CMRE’s underwater communication activities are supported on commercial, off-the-shelf (COTS) acousticmodems, a fundamental building block of the test bed are the modem tripods. These are 1 meter tall structures that currentlyhost the modems and the required interface electronics. The modems currently installed in each tripod are the Evologics S2C18-34 kHz that uses a coherent sweep-spread carrier modulation [13] and the FSK version of the WHOI micro modem [14]in the 20-30 kHz band. For the 2014 deployment and under the scope of the EU FP7 Sunrise project [15], the LOON tripodswere also fitted with Teledyne Benthos ATM 900 series modems [16] from the University of Rome - La Sapienza. Anotherfunctionality now provided is the possibility to record raw acoustic data at all the tripods with different either using the MicroModem wet-end and high definition audio interfaces or the built-in capability of the Benthos modem. One of the tripods is alsofitted with a Lubell LL916C underwater speaker which offers the possibility of arbitrary waveform generation in the audibleband. This feature is of particular interest for JANUS [9] testing and validation. For the 2014 deployment, USBL capabilitywas added to one of the Evologics Modems in order to provide an additional testing capability for localization techniques.

The node capabilities for the 2014 version of the LOON are pictured in Fig. 3.

B. Collaborative environment setup

The world-in-the-loop setup of the LOON in intended to be remotely accessible, allowing CMRE scientists, engineers andcollaborating institutions to log into the system, run experiments and collect data. This allows researchers across the communityto have access to deployed equipment, design experiments, create waveforms and collect data on a 24/7 basis. The network

Fig. 4. Biomass deposit between June (left) and November (right) 2011

support to achieve such functionality is supplied by CMRE’s information security specialists and IT support staff. The externalnetwork access is granted to a number of CMRE collaborators after agreeing to the terms of use and upon following anestablished procedure for authentication. In order to de-conflict the usage of the test bed, a centralized schedule of experimentsis maintained by CMRE and a locking mechanism is implemented in the command station to prevent concurrent use of thesystem.

IV. EXPECTED OUTCOMES, LESSONS LEARNT AND WAYS AHEAD

The value that can be harvested from a permanent test bed as the one presented in this work is, without a doubt, immense. Theposition of a research organisation such as CMRE, where 28 nations can find common ground for research and experimentationin the maritime domain can be explored not only by conducting development programmes but also by creating the means tofoster research and collaboration in the field. This is especially critical in the underwater domain where regulations, standardsand canonical models are lacking. The challenges of preparing, deploying, running and maintaining such a system should notbe overlooked and are a clear statement of the value that can be generated to the research community by “simply” makingthe test bed available. Having a relatively simple way to plug in sensors or other equipment, provides an additional levelof flexibility. The deployment of underwater test beds such as the LOON is a privileged mechanism to promote distributedcollaboration and cooperation in maritime research. Due to their long term nature, these test beds can mitigate the replicabilitydifficulties often faced by the common model of sea trials.

One of the most promising uses for an asset such as the LOON is to serve as a tool on which different institutions, researchgroups or commercial entities test their developments using pre-agreed honest-broker metrics, models and data-sets.

The improvements fitted to the LOON in 2014 are already playing an important role in testing the latest version of theproposed JANUS standard, currently reaching the final stages towards NATO standard promulgation.

Interesting observations have been made relative to bio-fouling. Figure 4 shows the same equipment in June 2011 (prior tothe LOON’s first deployment) and November 2011 when recovered for maintenance purposes. The amount of deposited biomass is impressive and to some degree explainable by the very warm summer and very shallow deployment.

During the first deployment, in 2011, the LOON was unavailable for 6 days of the total 10 months of experimentation (dueto maintenance and other cuncurrent experiments). This represents a test bed availability above 98% and was the main reasonbehind the decision of re-locating the LOON inside the Gulf of La Spezia.

The recently started EU-FP7 project SUNRISE [15] is pushing forward the concept of an underwater test bed federation.The LOON is the first infrastructure in the SUNRISE federation and will soon be joined by other test beds from consortiumpartners: One by the University of Porto, to be deployed in the north of Portugal, one by Suasis to be deployed in the BlackSea in the region of Kerpe - Turkey, one by the University of Twente to be deployed in a canal in the region of Twente andone by the University of Buffalo.

ACKNOWLEDGEMENT

The authors would like to acknowledge and thank all our CMRE colleagues that made the ACommsNet11, CommsNet12and CommsNet13 trials possible, our external collaborators for contributing to the development of the facility, the Italian Navyauthorities for the support throughout the whole period of tests. This research has been partially funded by the European UnionSeventh Framework Programme (FP7-ICT-2013-10) under grant agreement no. 611449.

REFERENCES

[1] J. Rice, B. Creber, C. Fletcher, P. Baxley, K. Rogers, K. McDonald, D. Rees, M. Wolf, S. Merriam, R. Mehio, J. Proakis, K. Scussel, D. Porta, J. Baker,J. Hardiman, and D. Green, “Evolution of seaweb underwater acoustic networking,” in OCEANS 2000 MTS/IEEE Conference and Exhibition, vol. 3,2000, pp. 2007–2017 vol.3.

[2] V. McDonald, J. Rice, and C. Fletcher, “An underwater communication testbed for telesonar rdt amp;e,” in OCEANS ’98 Conference Proceedings, vol. 2,sep-1 oct 1998, pp. 639 –643 vol.2.

[3] J. Alves, J. Potter, G. Zappa, P. Guerrini, and R. Been, “A testbed for collaborative development of underwater communications and networking,” inMilitary Communications Conference, 2012 - MILCOM 2012, Oct 2012, pp. 1–8.

[4] D. Merani, A. Berni, J. Potter, and R. Martins, “An underwater convergence layer for disruption tolerant networking,” in Internet Communications(BCFIC Riga), 2011 Baltic Congress on Future, feb. 2011, pp. 103–108.

[5] J. Alves and G. Zappa, “A low overhead message routing protocol for underwater acoustic networks,” in OCEANS, 2011 IEEE - Spain, june 2011, pp.1–10.

[6] J. Alves, A. Vermeij, D. Hughes, and G. Zappa, “Software-defined JANUS communication support for AUVs,” in Proceedings of the fourth InternationalConference and Exhibition on Underwater Acoustic measurements: Technologies and Results, 2011.

[7] J. Rice and J. Kalscheuer, “A selective automatic request protocol for through-water acoustic links,” in Proceedings of the fourth International Conferenceand Exhibition on Underwater Acoustic measurements: Technologies and Results, 2011.

[8] J. Gomes, E. Zamanizadeh, J. Bioucas-Dias, J. Alves, and T. Furfaro, “Building location awareness into acoustic communication links and networksthrough channel delay estimation,” in Proceedings of the 7th ACM International Conference on Underwater Networks and Systems. Los Angeles, CA,USA: ACM, 2012.

[9] Janus wiki: http://www.januswiki.org. [Online]. Available: http://www.januswiki.org[10] Moos-ivp homepage. [Online]. Available: http://www.moos-ivp.org[11] R. Masiero, S. Azad, F. Favaro, M. Petrani, G. Toso, F. Guerra, P. Casari, and M. Zorzi, “DESERT underwater: An ns-miracle-based framework to

design, simulate, emulate and realize test-beds for underwater network protocols,” in OCEANS 2012 Conference Proceedings, May 2012.[12] C. Petrioli and R. Petroccia, “SUNSET: Simulation, emulation and real-life testing of underwater wireless sensor networks,” in UCOMMS 2012 Conference

Proceedings, September 2012.[13] K. G. Kebkal and R. Bannasch, “Sweep-spread carrier for underwater communication over acoustic channels with strong multipath propagation.” Journal

of the Acoustical Society of America, vol. 112, no. 5 Pt 1, pp. 2043–2052, 2002.[14] L. Freitag, M. Grund, S. Singh, J. Partan, P. Koski, and K. Ball, “The whoi micro-modem: an acoustic communications and navigation system for

multiple platforms,” in OCEANS, 2005. Proceedings of MTS/IEEE, sept. 2005, pp. 1086–1092 Vol. 2.[15] The ec fp7 sunrise project. [Online]. Available: http://www.fp7-sunrise.eu/[16] Teledyne benthos acoustic modems. [Online]. Available: http://www.benthos.com/