Precision Clock and Time Transfer on a Wireless Telecommunication Link

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Precise time dissemination is a key requirement for remote clock synchronization used in coordinated command of distributed actuators in various applications. We present a newly conceived low-cost clock system based on the time-to-digital converter (TDC) principle to generate, transfer, and compare time-coded sequences (TCSs) with nanosecond accuracy using a wireless telecommunication link. The clock principle counts pulse sequences with nanosecond precision derived from a low-frequency oven-controlled crystal oscillator (OCXO) stable frequency standard. The TCSs are transmitted to a remote transponder that distributes them to receiving stations, where the clock readings are processed. A simple short-range wireless telecommunication link was assembled to demonstrate the system. The repeated TCSs are received back and compared with the reference clock. We describe the clock, the telecommunication setup, and the electrical and electronic sources of delays. Comparison of mean TCSs taken every 0.629 s provided a time-domain midterm stability Allan deviation of about <formula formulatype="inline"><tex Notation="TeX">$1.3 \times 10^{-11}$</tex></formula> at <formula formulatype="inline"><tex Notation="TeX">$\tau = 10^{3}\ \hbox{s}$</tex></formula>. These results show the feasibility of a low-cost GPS-independent technique, exhibiting highly performing time-domain midterm stability. This system is a key requirement for a new proposed system for geopositioning. </para>