Performance degradation in a quadrature receiver for cw signals corrupted by multipath

Abstract

In active sonar applications, a quadrature receiver can be employed to detect the presence of an underwater reflector. This well‐known receiver performs optimally when the input waveform is a coherent signal (i.e., constant but unknown amplitude and phase) embedded in white, Gaussian, zero‐mean noise. Unfortunately, when an attempt is made to detect a distributed highlight reflector in a multipath environment by using a sinusoidal transmit signal, the various multipath returns may overlap, producing a nonresolvable multipath situation and causing the amplitude and phase of the signal to become random functions of time. Under these circumstances, the detection performance of the quadrature receiver is degraded compared to its performance with a coherent signal. It is the intent of this paper to theoretically determine the degradation in the receiver’s output signal‐to‐noise ratio (SNR) when the input waveform consists of a narrowband Gaussian signal embedded in white Gaussian noise. The output SNR’s dependence on the correlation characteristics of the input signal is clearly shown.