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Compensating for Source Depth Change and Observing Surface Waves Using Underwater Communication Signals

Salman Ijaz ,Antònio Silva and Sèrgio .M.Jesus ssiddiqui@ualg.pt , asilva@ualg.pt, sjesus@ualg.pt
ISR-Universidade do Algarve, 8005-139 Faro, Portugal

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Ref.: Proc. SENSORCOMM 2010, (ISBN:), p., Venice, Italy,  2010. (to appear)

Abstract : Underwater communications impose great challenges due to the unpredictable changes in the environment. In order to accommodate for these changes, equalizers are used to track the Impulse Responses (IRs) and compensate the intersymbol interference (ISI). Source and array depth shifts are one of the major contributing factors to continuous amplitude and phase changes in IR. These changes magnify the problem of data processing in which correlation between successive received signals is involved, e.g. passive Time Reversal (pTR) where a probe signal is sent ahead of the data for post cross-correlation. In this paper, an environment based algorithm is used for pTR equalization, where an appropriate frequency shift of the estimated IR compensates for the geometric changes such as source and array depth shifts. We have applied this Frequency Shift pTR equalizer (FSpTR) on real data collected from Underwater Acoustic Barrier 2007 (UAB’07) sea trial having 1000 baud BPSK signaling at carrier frequency of 6.25 KHz with a sudden source depth change of 0.5 m at various known instants of time. The results illustrate that a considerable gain can be attained using the environment based equalizer in the presence of source and/or array depth changes. Moreover by close analysis of the FSpTR results we have detected surface wave motion through the frequency shifts caused by the array depth variations.

ACKNOWLEDGMENT: This work has been supported by European Community's Sixth Framework Programme through the grant to the budget of the Integrated Infrastructure Initiative HYDRALAB III within the Transnational Access Activities, Contract no. 022441. It was also supported by Portuguese Foundation for Science Technology under UAB (POCI/MAR/59008/2004) and PHITOM (PTDC/EEA-TEL/71263/2006) projects. The authors would like to thank the R/V Gunnerus master and crew, HYDRALB III and SINTEF personnel for their support during UAB’07.

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