HIGHFREQUENCY COHERENT ACOUSTICCOMMUNICATIONS FOR THE NETWORKED AUTONOMOUS LITTORALSURVEILLANCESYSTEM

TheNetworked Autonomous Littoral Surveillance (NetALS) system isawireless distributed bottom mounted sensor networkbeing developed atDRDCAtlantic. NetALSwill consist ofachain ofbottom mounted sensor clusters that rely on ultrasonic communications inbothsynchronous timedivision andasynchronous frequency division schemes totransferdetection statistics fromrelativley cheap sensor nodes tomorecapable cluster heads wheredata fusion anddecisionmaking takeplace. A channel estimation baseddecision directed (CE-DD) algorithm forphase coherent demodulation ofsensor data packets hasbeendeveloped. This multi-channel CE-DDreceiver relies onatimerecursive useofconjugate gradient iterations tosupport computationally reduced channel estimation andiscoupled toaLevinsonrecursion forcomposite channel adaptive equalization. Thealgorithm wastested onshallow water data withsource depth andbandwidth contraints aswellasreceiver ranges andapertures being consistent withabottom mounted sensornetwork. Computational reductions beyond that ofLevinson's O(M2)foradaptive filter construction lead toaslight performance degradation. Error rates forcommunication at 2and4bps/Hz arereported atranges from300mto800m withreceive phonesignal tonoise ratios between 8and22 dB.Theeffect oflimited aperture ontheacoustic communication link isdemonstrated.