Interferometric Imager Using Time-Shifted BPSK Codes
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Solution Overview
Problem
Existing active radar/lidar imaging systems require a large filled aperture to achieve high angular resolution, which is costly and impractical for many applications.
Innovation Solution
The use of two transmitters broadcasting time-shifted versions of a long binary-phase-shift-keyed (BPSK) code with a shift-and-add property, allowing for high angular resolution without a large aperture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large filled aperture is used to achieve high angular resolution, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent divides the imaging function into multiple transmitters (at least two) that broadcast time-shifted versions of a long BPSK code. Each transmitter acts as a separate segment that contributes to the overall imaging capability, eliminating the need for a single large filled aperture while maintaining high angular resolution through interferometric processing of the segmented signals.
Solution Approach 2:
The patent introduces the time dimension by using time-shifted BPSK codes with shift-and-add properties. Instead of relying solely on spatial aperture for angular resolution, the system uses temporal coding and time-difference-of-arrival measurements to achieve high angular resolution in a different dimension (time), thereby reducing the required spatial aperture size.
2Measurement precision
If transverse beam scanning is used to achieve 2-D imaging, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The patent uses periodic transmission of time-shifted BPSK codes from multiple transmitters to simultaneously illuminate the entire scene. This periodic action allows all angular information to be captured in parallel during each code period, eliminating the need for sequential beam scanning and significantly improving imaging productivity while maintaining high resolution through interferometric processing.
Solution Approach 2:
The system maintains continuous illumination of the scene by having multiple transmitters broadcast overlapping BPSK codes simultaneously. This continuous useful action ensures that all regions of interest are always being illuminated and measured, eliminating the gaps and sequential operations inherent in beam scanning methods, thereby improving imaging speed and productivity.
3Measurement precision
If real-aperture resolution is used for imaging, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses multiple transmitters that broadcast copies of the same BPSK code with different time shifts. These coded copies allow the system to achieve high angular resolution through temporal correlation and interferometric processing rather than requiring a physically large aperture, significantly reducing manufacturing cost and complexity while maintaining measurement precision.
Solution Approach 2:
The system changes the temporal parameters of the transmitted signals by using time-shifted BPSK codes with shift-and-add properties. This parameter change in the time domain allows the system to achieve high angular resolution through signal processing rather than through large spatial aperture, reducing the need for expensive large-aperture hardware and simplifying the overall system manufacture.
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 2-D imaging without transverse beam scanning or real-aperture resolution, providing a cost-effective and efficient method for active imaging.
Implementation Method 1
detecting, at the receiver, an interference signal produced from spatially-integrated interference between the first expanding speckle field and the second expanding speckle field
Implementation Method 2
The scene includes a scatterer that scatters the first diverging wave as a first expanding speckle field propagating from the scatterer toward a receiver
Data Source
AI summary
An imaging method includes: (I) simultaneously illuminating a scene with a first (second) diverging wave originating from a first (second) location and modulated with a first (second) shift-and-add-qualifying-code. A scatterer that scatters the first (second) diverging wave as a first (second) speckle. (II) Detecting, with a receiver, an interference signal, produced from interference between the speckle fields, and including a code temporally shifted with respect to the first SAA-code by a large-scale time-shift. (III) Circulantly correlating the interference signal with a reference SAA-code to generate a correlation signal. (IV) Determining the time-difference-of-arrival from the large-scale time-shift. (V) Determining a location of the scatterer by: determining, from the time-difference-of-arrival, a hyperbolic contour that locates the scatterer angularly; and determining, from one of (i) a small-scale time-shift of a peak of the correlation signal and (ii) a ranging delay, an elliptical contour that locates a range of the scatterer from the receiver.