Time-Reversal and Spatial Diversity: Issues in a Time-Varying Geometry Test

Underwater acoustic communications in waveguides is known to be prone to severe multipath, which strongly limits 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 usable form. This paper analysis the ability of such a peculiar matched filter to reject the unwanted terms both with fixed and timevarying source-receiver geometries. One particular parameter with practical interest is the sensitivity of the matched filter performance to a change of the source-receiver range during the processing that induces a mismatch limiting factor. Simulation examples in realistic situations and results obtained with real data, collected during the INTIFANTE’00 sea trial, illustrate the theoretical assertions.NATO Undersea Research Centre; Instituto Hidrográfico; FUP/Ministry of Defence; AOB - REA Joint Research Project; HFi - High Frequency Initiativ