Article Figures & Data
Figures
- FIGURE 1
Multi-platform clock ensemble block diagram
(Top) Four interconnected platforms have small atomic clocks (green circles) as onboard oscillators, and 2-GHz signals (blue arrows) are synthesized from the onboard clocks and transmitted between platforms. (Bottom) The Kalman filters and signal generation components necessary for timescale formation are shown. Differential phase measurements (solid yellow arrows) derived from the S band transmissions are input to a clock ensemble Kalman filter. A differential phase measurement between the NCO signal (gray arrow) and a 10-MHz clock signal from Platform 4 (green arrow) is added to the phase estimate (pink arrow) for the clock on Platform 4; this quantity represents the phase offset between the NCO and the IEM estimate, which is driven to zero via feedback frequency adjustments (red arrow) output from the steering Kalman filter to the NCO. The performance of the IEM realization is evaluated by measuring the NCO with respect to a rubidium reference oscillator.
- FIGURE 2
Measured ADEV for clocks in the ensemble
The NEL OCXO has the best short-term stability and is used as the reference clock for the IEM realization. The mRO has the best medium-term stability (10 s < τ < 250 s), and CSAC 01 has the best long-term stability (τ >250 s). The ensemble realization will have hybrid stability properties primarily derived from the OCXO, mRO, and CSAC 01. All clocks are measured against the rubidium oscillator, which is only for laboratory verification and is not part of the proposed system.
- FIGURE 3
Simulated results from Brown and Greenhall algorithms
The two algorithms produce different results for the same input clock ensemble members. The IEM produced from the Brown algorithm only tracks CSAC 1 whereas the IEM produced from the Greenhall algorithm has a hybrid stability profile derived from both the mRO and CSAC 1.
- FIGURE 4
ADEV of the target state and steering results from separate experiments using two different steering methods
The steered result for Test 1 (solid red line) uses an 18-bit DAC to electronically steer the OCXO to the target state (dashed red line). The steered result for Test 2 (solid blue line) uses an NCO approach to steer the signal to the target state (dashed blue line). The steered result for Test 2 yields a better result than Test 1 because of the more precise resolution of the frequency adjustment commands.
- FIGURE 5
Simplified view of clock ensemble hardware showing the four platforms and the respective onboard clocks that form the clock ensemble
- FIGURE 6
ADEV of the three CSACs (dashed blue) and mRO (solid blue), which are the four ensemble member clocks
The OCXO (gray) is the external reference clock for the NCO, which generates the IEM realization (red). The simulated IEM (black) from Figure 3 is used here as a benchmark to evaluate system performance.
Tables
Noise Parameter CSAC 1 CSAC 2 CSAC 3 mRO q1 (s) 8.1 · 10−21 4.0 · 10−20 4.0 · 10−20 1.6 · 10−21 q2 (s−1) 1.6 · 10−27 1.7 · 10−26 1.7 · 10−26 6.9 · 10−26 CSAC 1 CSAC 2 CSAC 3 mRO 0.14 0.03 0.03 0.80
Jump to section
Related Articles
Cited By...
- No citing articles found.