Extremely High-accuracy Automatic Following between Mobilities Using Wireless Two-way Interferometry

We propose equiphase distance following, which is a method to keep a constant distance between mobilities by seeking the position at a certain phase of a carrier wave by using wireless two-way interferometry (Wi-Wi). Wi-Wi offers a high-precision phase sensing capability and leads on to ranging on the order of millimeters. Exploiting this advantage, a millimeter-precision automatic following technique is promising in spite of the used bandwidth of 200 kHz in the 920-MHz band. For stable following behavior, the influence of wireless environment upon the phase sensing capability of Wi-Wi is considerable issue to be examined. In this paper, we investigated the effect of an AWGN channel and co-channel interferences on the error and dispersion of phase detection. The root mean squared error of the detected phase was independent of the magnitude of CNR/CIR, and was kept at the original performance of 1-mm accuracy. The dispersion also stayed almost constant at 4.5 mm as long as CNR/CIR is greater than 10 dB, and otherwise increased rapidly as the channel degraded. Finally, we discuss about a smoothing filter for suppressing this dispersion, and have demonstrated constant-distance following with the accuracy of 5 mm.