Nanosecond Relative Time Offset Measurement System
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Solution Overview
Problem
Current time synchronization systems, relying on atomic clocks and GNSS, achieve only about 20 nanoseconds of ultimate accuracy, which is insufficient for sub-meter location finding applications that require one nanosecond or better time difference measurement accuracy.
Innovation Solution
A method and system for continuous and instantaneous relative time measurement between non-collocated frequency sources, achieving nanosecond-level accuracy by disciplining frequency drift and using a single difference technique to compute time offsets, with known positions of timing units and external signal streams for pseudo-range and Doppler sample pairs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If atomic clock with GNSS aiding is used for time synchronization, then time synchronization capability is provided, but ultimate time synchronization accuracy is limited to about 20 nanoseconds
Solution Approach 1:
The system divides the time synchronization problem into two independent components: (1) frequency drift correction using GNSS aiding at a frequency domain, and (2) time offset measurement using common view technique at a time domain. This segmentation allows each component to be optimized independently, achieving nanosecond-level time offset measurement accuracy while using conventional atomic clocks with GNSS aiding.
Solution Approach 2:
The patent introduces an intermediary measurement approach by using a common external signal (such as a GNSS satellite signal) as a reference mediator between two or more atomic clocks at different locations. By measuring the time differences of the same external signal arriving at different receivers, the system can determine relative time offsets with nanosecond accuracy without requiring the clocks themselves to be perfectly synchronized.
2Adaptability or versatility
If conventional time synchronization systems are used, then time synchronization is provided, but time measurement accuracy is insufficient for sub-meter location finding applications
Solution Approach 1:
The system changes the measurement parameter from absolute time synchronization accuracy to relative time offset measurement accuracy. By focusing on measuring the time difference between signals arriving at different receivers rather than maintaining absolute clock synchronization, the system achieves nanosecond-level precision suitable for sub-meter location finding applications.
3Stability of the object's composition
If frequency drift disciplining is applied at frequency domain, then frequency drift between frequency sources is corrected, but measurement of time offset at nanosecond level requires additional constraints
Solution Approach 1:
The system performs preliminary frequency drift correction in the frequency domain using GNSS aiding before conducting time offset measurements. By pre-disciplining the frequency sources and ensuring their drift is limited to one order of magnitude less than the required time measurement accuracy, the system simplifies the subsequent time offset measurement process and reduces the complexity of real-time correction requirements.
Data Source
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AI summary
A system for instantaneous and continuous nanosecond-level accuracy determination of a relative time offset between at least two non-collocated timing units, the system comprising at least two non-collocated timing units located at known positions, each timing unit comprising a frequency source and a collocated receiver, each frequency source being disciplined at a frequency domain using a time source to generate corrections of the relative frequency drift between the frequency source and the time source so as to be limited by the following condition: the product of a duration of any time period extending between adjacent discrete points of time in a sequence of discrete points of time, multiplied by the sum of all frequency corrections effected during the time period and divided by a frequency value characterizing the frequency sources, is at least one order of magnitude less than the required accuracy, each receiver being synchronized by a synchronization signal supplied by the frequency source and being operative to receive an external signal stream defining a time-line and to derive therefrom a stream of pseudo-range sample and integrated Doppler sample pairs, to generate, for each individual pair in at least a subset of the pairs, a periodic pulse synchronized with the frequency source, thereby to define a periodic pulse corresponding to the individual pair and to output each individual pair in the subset, simultaneously with the individual pair's corresponding periodic pulse; and at least one time offset computation unit operative to use the timing units' known positions and at least one sample pair from each of the timing units in order to compute time offset between periodic pulses generated by the two timing units respectively, using a single difference technique.