Time reversal and spatial diversity: issues in a time varying geometry test

S.M. Jesus and A. Silva sjesus@ualg.pt  and asilva@ualg.pt
SiPLAB-FCT, Universidade do Algarve
Faro, Portugal

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Ref.: Proc. Conf. on High Frequency Ocean Acoustics, (Am. Inst. of Physics), Porter, Siderius and Kuperman (eds), (ISBN:0-7354-0210-8) p.530-538,  San Diego (USA), March 2004.

Abstract : Underwater acoustic communications in waveguides is known to be prone to severe multipath, which strongly limitates practical transmission rates with actual channel equalization techniques. The time reversal principle uses the ocean waveguide response to a basic pulse shape to matched filter the received data sequence. Assuming the ocean response to be a version of the actual pulse shape ocean response corrupted by additive noise, the matched filter output remains a sum of four terms from which only one has the required data sequence in useable form. This paper analyses the ability of such a peculiar matched filter to reject the unwanted terms both with fixed and time-varying source-receiver geometries. One particular parameter with practical interest is the sensitivity of the matched filter performance to a drastic reduction of the number of acoustic sensors which induces a spatial diversity limiting factor. Simulation examples and results obtained with real data, collected during the INTIFANTE'00 and the MREA'03 sea trials, are shown to demonstrate the theoretical assertions.

ACKNOWLEDGMENT: this work was partially supported by FUP/Ministry of Defence  program under project LOCAPASS and AOB - REA Joint Research Project.