Bi-Static Radar Frequency Offset Estimation Using Doppler Reciprocity
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Solution Overview
Problem
Existing coherent distributed radar systems face challenges in accurately estimating and correcting fine frequency offsets between bi-static radar transmitters due to differences in clock signals, which affect signal processing and target velocity measurements.
Innovation Solution
A bi-static radar system employs a common clock signal between two radar stations, utilizing the reciprocity of bi-static radar scenes to estimate frequency offsets by comparing target velocities, allowing for correction without requiring sequential upchirps and downchirps, and using any strong target for estimation instead of a dedicated reference target.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a common clock signal is used to generate transmit signals in bi-static radar scenarios, then system coherence and synchronization are improved, but frequency offset differences between transmitters occur due to clock signal variations
Solution Approach 1:
The system estimates frequency offsets by comparing Doppler frequencies of the same target detected by both radar stations, using the reciprocity principle. The frequency offset is calculated as half the difference between the two Doppler measurements, providing feedback to correct the clock signal variations and maintain coherence.
Solution Approach 2:
A reference target is introduced as an intermediary to enable frequency offset estimation. By measuring the Doppler frequency of a known reference target at both stations, the system can calculate the frequency offset without requiring direct comparison of transmit signals, thus resolving the synchronization issue.
2Measurement precision
If frequency offset estimation is performed using traditional methods requiring sequential upchirps and downchirps, then frequency offset can be estimated, but system complexity and processing time increase
Solution Approach 1:
The system performs frequency offset estimation using the reciprocity principle and Doppler frequency comparison of reference targets before the main radar processing. This preliminary action allows the frequency offset to be pre-calculated and stored, eliminating the need for complex sequential chirp sequences during actual target detection.
Solution Approach 2:
The invention changes the estimation approach from time-domain sequential chirp modulation to frequency-domain Doppler comparison. By transforming the problem into a frequency parameter comparison using the reciprocity principle, the system achieves frequency offset estimation without requiring sequential upchirps and downchirps, reducing processing complexity.
3Measurement precision
If a dedicated reference target is used for frequency offset estimation, then frequency offset can be accurately estimated, but system resources and complexity increase
Solution Approach 1:
The system makes any strong detected target usable for frequency offset estimation, not just a dedicated reference target. By using the reciprocity principle, any target with sufficient signal strength can serve the dual purpose of both radar detection and frequency offset calibration, eliminating the need for separate dedicated reference targets and reducing system complexity.
Solution Approach 2:
The radar system uses its own detected targets to perform frequency offset estimation. Instead of requiring external dedicated reference targets, the system leverages the targets it already detects during normal operation, allowing the system to self-calibrate without additional external resources or complex configuration.
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 method effectively corrects frequency offsets, simplifies system complexity, and extends to multi-static radar scenarios, ensuring accurate target velocity measurements and coherent ranging without additional system requirements.
Implementation Method 1
coherently process the reflected first radar signal to produce a first doppler frequency for a reference target
Data Source
AI summary
Various embodiments relate to a bi-static radar system, including: first and second radar stations configured to: transmit first and second radar signals based upon a clock signal; wherein the first radar station receives a reflected second radar signal and the second radar station receives a reflected first radar signal; coherently process the reflected first and second radar signals to produce a first and second doppler frequency for first and second reference targets, wherein the first and second reference targets are is a detected target with the greatest signal strength; generate a frequency offset estimate based upon the average of the first and second doppler frequencies; frequency shift the reflected second radar signal by the frequency offset estimate to produce a corrected second radar signal; and coherently process the corrected second radar signal to produce first radar outputs from the first radar station.