On real-time optimal FIR estimation of linear TIE models of local clocks. 
In this paper, we present an optimal finite-impulse response (FIR) filter for the linear time-interval error (TIE) model of a local clock and compare its estimates to those obtained by the unbiased FIR filter via the global positioning system (GPS)-based sawtooth measurements.  We show theoretically and verify experimentally that there is no reasonable necessity in using optimal filters for GPS-based estimation of the TIE of precision crystal, rubidium, and cesium clocks.  For these clocks, the optimal FIR filter requiring four coefficients degenerates to a simple unbiased FIR filter requiring only one coefficient.