Method and system for distance measurement in a low or zero intermediate frequency half-duplex communications loop

Abstract

A method and system for distance measurement in a low or zero intermediate frequency (IF) half-duplex communications loop measures the distance between two transceivers without synchronizing the local oscillators of the two transceivers. Transceiver distance may be measured in systems that use direct conversion (zero IF) or intermediate frequencies that are so low that phase noise significantly reduces the accuracy of the distance measurement. The communications loop demodulates, re-modulates and retransmits a received signal to provide a re-transmitted signal that has the same carrier and modulation frequency as the received signal. A phase-hold circuit provides an analog system for half-duplex operation that retains the frequency and phase information of the received signal for retransmission in a subsequent time slot. Alternatively, a digital implementation provides phase and frequency retention via a sample and delay system comprising an analog-to-digital conversion (ADC) subsystem, a first-in-first-out (FIFO) memory and a digital-to-analog (D/A) converter.