Kun-Yuan Tu

Frequency syntonization using GPS carrier phase measurements

A new methodology of frequency syntonization using GPS carrier phase double differences is presented. The proposed scheme can achieve the traceability of frequency dissemination and obtain the very high frequency stability in the short term, as well as in the long term. The GPS receivers used in our system were elaborately modified in order to estimate the frequency offset of the remote low-cost oven-controlled crystal oscillator clock with respect to the primary cesium atomic clock in real time by performing the double differences on the GPS carrier phase observables. The fuzzy controller and the proportional-derivative controller were employed to implement the controllers of our system, respectively. Through the D/A converter, the remote clock was then steered to synchronize with the primary clock. For averaging times of one day under the configuration of about a 30-m baseline, our experimental results show that the accuracy of the remote clock can be improved from about 3/spl times/10/sup -9/ to about 3/spl times/10/sup -14/, and the stability of the remote clock can be improved from about 3/spl times/10/sup -10/ to about 2/spl times/10/sup -14/. Moreover, the 30-m baseline tests with the common high-performance cesium clock revealed that our system has a frequency stability of about 2/spl times/10/sup -16/ for averaging times of one day.

Remote frequency control via IEEE 1588

A new scheme of remote frequency control based on the IEEE 1588 standards, a precision time synchronization protocol (PTP) is proposed in this paper. A remote oven-controlled crystal oscillator (OCXO) is steered by integrating the PTP system, fuzzy controller and D/A converter, such that its frequency can follow a primary cesium atomic clock used as the master clock of the PTP system. Experimental results show that for averaging times of one day, the frequency stability of the OCXO can be improved from a few parts in 109 to 1012.

Formation of a paper neural-fuzzy time scale in the eastern Asia

This work presents a novel scheme to simulate a paper time scale by utilizing ensemble clock data of time laboratories in the eastern Asia-Pacific region. Based on integration of the above data with a neural-fuzzy prediction approach, the time difference with a local coordinated universal time is analyzed by a reference time scale devised in this work. Validity of the proposed scheme is investigated by undertaking a 250-day long neural-fuzzy predictor that is based on the calculated clock ensembles from Asian time laboratories. In the Asia-Pacific rim region, TWSTFT links from four laboratories, including the National Institute of Information and Communications Technology of Japan (NICT), the National Time Service Center of China (NTSC), the Korea Research Institute of Standards and Science of Korea (KRISS), and the Telecommunication Laboratories of Taiwan (TL), have formed a time transfer network based on use of multi-channel TWSTFT time transfer modems. Thus, a paper neural-fuzzy reference time scale by using the ensemble clock data among NICT, NTSC, KRISS, and TL in the Asia-Pacific region is simulated. Moreover, the performance of the proposed time scale is evaluated.

Frequency Calibration Based on the Adaptive Neural–Fuzzy Inference System

A new scheme of frequency calibration based on adaptive neural-fuzzy inference system (ANFIS) is proposed in this paper. In normal mode, an oven- controlled crystal oscillator (OCXO) is steered by integrating time interval counter (TIC), fuzzy controller, D/A converter, etc., such that its frequency can follow a primary cesium atomic clock. In addition, the ANFIS is applied when the system enters holdover mode. Experimental results show that the frequency stability of the OCXO can be improved from a few parts in 109 to 1013 for averaging times of one day, as well as the performance could be maintained within a few parts in 1010 over one day in the holdover mode.

Formation of a Real-Time Time Scale With Asia-Pacific TWSTFT Network Data

This paper presents a novel scheme to generate a real-time paper time scale by utilizing ensemble clock data and two-way satellite time and frequency transfer (TWSTFT) data of time laboratories in the Asia-Pacific region. Based on integration of the aforementioned data with a specific weighting method and a fuzzy prediction approach, the reference paper time scale devised in this paper can be generated in real time. The validity of the proposed scheme is investigated by undertaking about one years worth of experiments, which are based on the calculated clock ensembles from TWSTFT links among Asian time laboratories. Moreover, the performance of the proposed scheme is evaluated with respect to the time scales of Coordinated Universal Time (UTC) and local realizations of UTC. The simulated real-time reference time scale based on the proposed scheme is within 10 ns with UTC, and time deviation is less than 0.6 ns for a time interval exceeding 60 days.

Design and Implementation of a Switching Controller for Transient Improvement in a Time Synchronization System

Currently, many large and complex systems, such as telecommunication systems, power systems, and automated manufacture systems, require their distributed clocks to be synchronized to the master clock. This paper discusses implementation of a distributed embedded time-synchronized system, based on the IEEE 1588 standard. Two important requirements exist in time synchronization. One is that the clocks be synchronized at maximum speed. The other is that the clocks operate at optimum precision and accuracy over the long term. This paper proposes a switching controller, which combines a fuzzy control scheme and a traditional proportional integral (PI) control scheme to meet the aforementioned two requirements. The traditional PI control scheme was used in the steady state, whereas the fuzzy control scheme was adopted in the transient stage. The experimental results showed that in the fuzzy control scheme, transient time, which is the length of time in the transient state, was reduced to 50% of the transient time in the PI control scheme.

Implementation of switching controller for precise network time synchronization

Nowadays, many devices are equipped with computer network interfaces. Some systems of area such as security of finance and real-time communication, synchronizing distributed clocks, rapidly, to enable their operations is imperatively required. The implementation of distributed embedded architecture which is based on IEEE 1588 standard to achieve a precise time synchronizing system is investigated. The switching controller which is combined with fuzzy and PI control schemes is proposed to reduce the time offsets from the master clock to slave clocks. The long transient time is improved with minute level via the fuzzy control. The small magnitudes of steady-state errors are reserved, completely, via the PI control.

Highly-accurate real-time syntonization using a GPS single-frequency receiver with an intelligent atmosphere forecasting model

A low-cost, highly-accurate real-time GPS carrier phase frequency syntonization system based on a single-frequency receiver is presented. By using the atmosphere free model of the carrier phase with the neural-wavelet filter, and performing the time-difference operation, the low-cost oscillator can be automatically steered to obtain very high frequency accuracy and stability in the short term (1 sec.) as well as in the long term (1 day).