AquaTools: An Underwater Acoustic Networking Simulation Toolkit

Abstract—High cost of development and deployment coupledwith the complexity of the underwater acoustic channelmakes it important to develop simulation tools which canassist in investigating underwater sensor networks and mobileautonomous underwater vehicular communications. Some recentdevelopments have led to simulators which provide theability to simulate mobile and stationary underwater acousticcommunication, however, they do not take into account factorssuch as ocean acidity, salinity and temperature, which too haveeffects on the channel. In this paper we present an overview onthe AquaTools simulation toolkit, some background on channelmodels utilized and an excerpt of the results obtained duringtesting and validation of the simulator. I. I NTRODUCTION The radio or optical channels are not efficient underwatersince radio waves require very low transmission frequencies(30-300 Hz), very long antennae and high transmissionpower, while optical communication is usable only for shortrange communications due to the high signal attenuation.Consequently, the acoustic channel has become a commonchoice for wireless underwater communication.However, volatility of channel conditions leads to highand varying ambient noise and high localized fluctuations inpropagation delay due to the dependence of sound velocityon ambient temperature, salinity and acidity. Surface-bottommulti-path echoes, low-transmission speeds, narrow bandwidthand high bit-error-rates create challenges for dependablecommunication in the underwater acoustic channel [1]. Thismakes exhaustive testing of any underwater network necessaryto ensure reliable communications.Fabrication and off-shore deployment costs associated withunderwater networks can be quite high. The costs of adependable underwater acoustic modem are in the orderof several thousand dollars, and off-shore deployment andrecovery from a small boat can be in thousands per day. Suchhigh costs associated with off-shore testing can be a baneto development in case revisions are necessary [2]. Thesecosts coupled with complexity of the channel highlight theneed for a simulator to accurately model the rapidly changingunderwater acoustic channel. This would assist in developmentof systems and reduce off-shore deployment times.Furthermore, in recent times Autonomous UnderwaterVehicles (AUVs) have gained acceptance for deployments inoff-shore research and exploration tasks. However, as in theterrestrial and aerial robotics fields, the maximum potential forunderwater unmanned vehicles lies in cooperative multi-AUVtasks. There are also some emerging scenarios involving theuse of AUVs as data mules in an underwater sensor network.The addition of mobile communication networks increases thecomplexities of underwater networks. Any simulator must, assuch, have the ability to simulate not just static, but also mobilenodes.Even though tools like MATLAB are very useful inunderstanding channel characteristics, they fall short of beingable to simulate networking performance as a result ofthe chosen MAC layer, routing protocol and other similarparameters; they cannot even provide network traces withoutmuch effort. As such, it is necessary to develop simulatorswhich can evaluate underwater acoustic communications froma networking perspective as well.The recent simulators capable of performing networksimulations [3], [4] do not take into account ambienttemperature, node depth, ocean acidity and salinity whilecharacterizing the channel, however, these parameters areknown to have an effect on channel performance [5], [6].Restrictions on the choice of MAC layer or absence ofrouting layers also point toward needed improvements. Assuch, the AquaTools simulation toolkit was developed toovercome these shortcomings. The AquaTools toolkit is basedon ns2, a popular networking simulator and can as such makeuse of any MAC layer, routing layer, energy conservationschemes and other developments for the ns2 simulator as well.The AquaTools toolkit simulations can be setup via scriptsand any acoustic modem’s characteristics can be simulatedby providing the appropriate parameters. Different mobilitymodels can also be incorporated into the simulation.This paper provides an overview of the different propagationand channel models utilized by the AquaTools simulationtoolkit. Details on the design and usage of the AquaToolssimulation toolkit will also be discussed along with someresults obtained during validation and testing of the simulator.II. R