Phase-difference ambiguity resolution for a single-frequency signal

In this letter, we propose a novel method to disambiguate the phase-difference of a single-frequency signal observed between a pair of spatially separated sensors, with inter-sensor spacing exceeding half the wavelength (λ/2) of the signal. We mathematically prove that, in a noiseless case, the true phase-difference can unambiguously be estimated utilizing a third collinear sensor, provided that the absolute difference between the two smaller inter-sensor spacings is less than λ/2. The performance of the method is characterized by estimating the probability of failure in noisy cases.