Phase alignment for coherent and vector processing

Abstract

Acoustic phase angle is seldom used to achieve signal-to-noise ratio (SNR) gain for single sensor and beam spectral output. One reason is that phase angles generally progress at a nonuniform rate, with unpredictable changes in the direction of rotation. This causes fluctuations in the phase angles with corresponding reductions in gain, often including severe attenuation and cancellation of signals. By adopting a particular analytically convenient definition for phase fluctuations, the fluctuations, thus defined, constitute a set of aligned-phase angles. The aligned-phase angles can be used instead of phase angles to form phase-aligned coherent and vector averages. Doing so achieves SNR gains that equal or exceed the theoretical value of 10 log(N) for perfectly coherent vector averaging (N is the number of elements averaged). This is accomplished without the signal attenuation and cancellation common to coherent and vector averaging. Furthermore, the aligned-phase angles can also be used to automatically detect signals, based on both phase-aligned coherence and appropriate averaging of the aligned-phase angles. Results are included for wind noise in outdoor measurements. [Work supported by U.S. Army Space and Missile Defense Command.]