Pulse Doppler Coherent Integration for Unambiguous Range and Velocity
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Solution Overview
Problem
Current pulse Doppler coherent systems face challenges in achieving maximum signal-to-noise ratio (SNR) and unambiguous measurement of target range and velocity due to the limitations of single Pulse Repetition Frequency (PRF) schemes, which result in blind zones and reduced detection efficiency when using multiple PRFs for simultaneous measurement.
Innovation Solution
A two-step coherent integration method is employed, involving a discrete Fourier transform followed by complex value interpolation and Doppler phase correction, allowing for the summation of unfolded range-Doppler matrices from multiple Coherent Processing Intervals (CPIs) to enhance SNR and enable simultaneous measurement of target kinematical parameters without intermediate detection decisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple PRF sequences are transmitted to resolve ambiguity in range and velocity measurement, then unambiguous measurement capability is improved, but the coherent integration time is reduced and detection probability deteriorates
Solution Approach 1:
The time-on-target interval is segmented into multiple Coherent Processing Intervals (CPIs), each using a different PRF sequence. This allows ambiguity resolution across multiple PRFs while maintaining coherent integration within each CPI. The segmentation enables simultaneous achievement of unambiguous measurement and adequate integration time by distributing the integration process across multiple segmented intervals with different PRFs.
Solution Approach 2:
The patent merges the results from multiple CPIs with different PRFs by combining their range-Doppler matrices through complex value interpolation and phase correction. This merging process integrates the benefits of multiple PRFs for ambiguity resolution while accumulating the energy from all CPIs to maintain high detection probability, effectively combining the measurement precision benefits with the reliability benefits.
2Reliability
If a single constant PRF is used for pulse transmission, then coherent integration over the entire time-on-target interval is maximized, but unambiguous measurement of range and velocity cannot be achieved
Solution Approach 1:
The system employs periodic transmission of pulse sequences with different PRFs in a cyclic manner across multiple CPIs. This periodic alternation between different PRF sequences allows the system to maintain coherent integration within each CPI while periodically switching PRFs to resolve ambiguities, achieving both high detection capability and unambiguous measurement through the periodic structure.
Solution Approach 2:
The patent changes the PRF parameter periodically across different CPIs while maintaining coherent processing within each CPI. By varying the PRF parameter in a controlled manner across multiple intervals and then combining the results through phase correction and interpolation, the system achieves unambiguous measurement without sacrificing the coherent integration benefits that require parameter stability within each processing interval.
3Measurement precision
If multiple independent PRF sequences are used for ambiguity resolution, then measurement capability is improved, but time-on-target is partitioned into smaller sub-intervals reducing energy collection
Solution Approach 1:
The patent maintains continuous coherent integration across all CPIs by using complex value interpolation and phase correction to combine results from multiple PRF sequences. This continuity of useful action ensures that energy from the target return is accumulated across the entire time-on-target interval rather than being lost in independent processing of separate sub-intervals, thereby maximizing energy collection while maintaining ambiguity resolution capability.
Solution Approach 2:
The system performs preliminary coherent integration within each CPI using the specific PRF for that interval, storing the intermediate results in range-Doppler matrices. These preliminary actions are then combined through phase correction and interpolation to achieve the final integrated result. This preliminary action approach allows energy accumulation across all CPIs while maintaining the measurement precision benefits of multiple PRFs.
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 maximizes the integration results by maintaining coherence throughout the entire time-on-target interval, improving detection range and probability while avoiding the losses associated with prior art methods, thereby enhancing the overall SNR and detection capability.
Implementation Method 1
a discrete Fourier transform is performed on the signal to generate a signal spectrum
Implementation Method 2
The pulse Doppler technique is common to most modem surveillance and tracking radars... This technique is particularly convenient when the velocity of the target is significantly different from the velocity of the background scatterers
Data Source
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AI summary
A method and system for SNR enhancement in pulse-Doppler coherent target detection. In accordance with the method of the invention, complex signals are obtained for each of two or more sub-intervals of the time-on-target interval, allowing simultaneous rang and Doppler measurements. A coherent integration is then performed on the signals to generate complex-valued folded matrices. The folded matrices are unfolded and target detection is then performed in a process involving one or more of the unfolded matrices. A pulse-Doppler coherent system is also provided configured for target detection by the method of the invention.