Non-uniform Pulse Sampling for Unambiguous Doppler Velocity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Laser detection and ranging systems face ambiguity in measuring the range rate of targets due to Doppler ambiguity, which affects their accuracy in commercial and military applications.
Innovation Solution
A method is introduced to remove Doppler ambiguity by offsetting the time of each pulse in a sequence of transmitted pulses, representing received pulses as complex numbers, multiplying them by correction factors based on time offsets and test frequencies, and performing Fourier transforms to generate a corrected spectrum array, allowing for unambiguous Doppler velocity measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If uniform pulse sampling is used in ladar system, then the system operation is simple, but Doppler ambiguity occurs and measurement precision deteriorates
Solution Approach 1:
The patent applies asymmetry by using non-uniform pulse timing offsets instead of uniform spacing. Each pulse in the sequence is transmitted at a time offset that breaks the symmetry of uniform sampling, which eliminates Doppler ambiguity while maintaining system operability through structured asymmetric patterns
Solution Approach 2:
The patent changes the temporal parameter of pulse transmission by introducing variable time offsets between pulses. This parameter change from uniform to non-uniform timing allows the system to resolve Doppler ambiguity while maintaining practical operation through controlled parameter variation
2Measurement precision
If non-uniform pulse sampling is used to remove Doppler ambiguity, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction factors corresponding to each possible time offset before signal processing. During operation, the system simply retrieves and applies the appropriate correction factor based on the actual timing offset, avoiding complex real-time calculations and reducing processing complexity
Solution Approach 2:
The patent introduces correction factors as an intermediary element between the non-uniformly sampled signal and the final Doppler measurement. These correction factors act as a mediator that compensates for the non-uniform sampling effects, simplifying the overall processing by decoupling the timing variation from the measurement calculation
3Adaptability or versatility
If traditional uniform sampling is used, then hardware requirements are met, but simultaneous range and Doppler measurement in absolute scale is not achieved
Solution Approach 1:
The patent uses another dimension by measuring both range and Doppler velocity from the same non-uniformly sampled pulse sequence. Instead of requiring separate measurement systems, the method extracts both parameters from the temporal structure of the pulse timing offsets, adding a dimension of measurement capability without additional hardware
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate and unambiguous Doppler velocity measurement, simplifying hardware requirements and allowing simultaneous determination of target range and Doppler in an absolute scale, reducing measurement timelines and improving system accuracy.
Implementation Method 1
A laser detection and ranging system may transmit a sequence of short pulses of light, and detect return pulses that are formed when the transmitted pulses reflect from a target. Such a system may be affected by Doppler ambiguity, i.e., from an inability to unambiguously determine the range rate of the target from the return pulses.
Data Source
AI summary
A method for removing Doppler ambiguity in a ladar system. The time of each pulse of a sequence of transmitted pulses is offset from that of a uniform sequence of pulses. Each received pulse is represented by a complex number corresponding to its amplitude and phase, and each complex number of the resulting array of complex numbers is multiplied by a complex correction factor having a phase proportional to (i) the time offset of the corresponding pulse, and to (ii) a test frequency of an array of test frequencies, to form a second array of complex numbers. A Fourier transform of the second array is taken, and the value at the test frequency is copied into a corrected spectrum array. The process is repeated for each test frequency in the array of test frequencies, to generate a complete corrected spectrum array.