Multichannel Signal Detection in Time-Spreading Distortion Underwater Channels Using Vector and Scalar Sensors: Theory and Experiments

Underwater signal detection in shallow water needs to be able to handle several types of distortion. One is the time-spreading distortion (TSD), in which several replicas of the transmitted signal arrive at different times, as a result of the signal traveling over multiple propagation paths. In this article, we present a multichannel signal detector for TSD channels. The performance of the detector is first studied analytically, by deriving closed-form equations for the detection and false alarm probabilities of the multichannel detector in TSD channels. The detector's performance is further evaluated via computer simulations and underwater experiments. Two types of multichannel receivers are used in the underwater experiments. The first one is a sphere vector sensor that measures the vector components of the acoustic field, i.e., the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i>, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i>, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> acoustic particle velocities, as well as the scalar component of the acoustic field, that is, the acoustic pressure, whereas the second one is composed of scalar sensors, which are hydrophones that measure only the scalar component of the acoustic field. Our results indicate that, as the number of channels of the receiver increases, the detection probability in TSD channels increases and, furthermore, the detection probability becomes less dependent on the choice of the required number of correlators for each channel of the receiver. Given the multichannel nature of a small-size vector sensor, such a sensor can serve as an effective and compact multichannel signal detector in TSD channels. This can be of particular importance in small underwater platforms that have considerable size constraints.