Coherent and Incoherent Integrations for Autocorrelation Measurement Under Stochastic Multipath Propagation (Random Process, Probability of Detection, Receiver, Transmitter, Correlation).
Richard Benjamin Lee · Deep Blue (University of Michigan) · 1986
In long range underwater acoustics, any point in the ocean receives sound that has travelled via multiple paths, each carrying different amounts of sound energy and having different travel times. The autocorrelation function describes one aspect of the effect of multipath fluctuations. This function, with its principal parameter, the channel correlation time, is very useful in operational and detection models. This dissertation analyzes the effects of fluctuation in multipath gain and delay on the measurement of the autocorrelation function. The specific autocorrelation measurement analyzed employs both coherent and incoherent integrations. The ultimate goal of the measurement is to measure the channel correlation time as accurately as possible. Two major issues that one often encounters are addressed and studied: output signal to noise ratio and the effect of coherent integration on the measured channel correlation time, i.e., how to recover the true channel correlation time from the measured one. The proper durations of the integrations to achieve an accurate measurement are gauged by the output signal to noise ratio of the autocorrelator. In order to compute the output signal to noise ratio we model the multipath amplitudes and delays by complex-valued and real random processes respectively. The major contribution of this work is the computation of output signal to noise ratio under multipath propagation. This is shown to be the same under single path and i.i.d (independent and identically distributed) multipath propagation. The linear and quadratic regions of processing gain vs. input signal to noise ratio, and the dominance of amplitude or time delay fluctuations are investigated. It is found that the measured channel correlation time consists of the true channel correlation time plus a term proportional to coherent integration time.