Coherent LADAR Doppler Compensation via Local Oscillator Waveform
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Solution Overview
Problem
Coherent LADAR systems face challenges in accommodating large Doppler shifts caused by velocity differences between sensors and objects, often requiring excessively large receiver bandwidths to capture signal information effectively.
Innovation Solution
Representing the range of Doppler frequency offsets as a local oscillator waveform comprising digital samples and adjusting the start and stop of frequency modulation, along with timing, to compensate for target Doppler shifts, allowing the system to maintain signal capture within a reduced receiver bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the receiver bandwidth is increased to accommodate large Doppler shifts, then the system can capture signals with large velocity differences, but the device complexity and cost increase
Solution Approach 1:
The patent changes the parameters of the local oscillator waveform by representing Doppler frequency offsets as a series of digital waveform samples with different frequency characteristics. The system selects and applies appropriate waveform samples based on detected Doppler values, dynamically adjusting the local oscillator parameters to match the received signal characteristics without requiring excessive receiver bandwidth
Solution Approach 2:
The system dynamically adjusts the local oscillator waveform parameters in real-time based on detected Doppler shifts. By selecting from a library of pre-computed waveform samples corresponding to different Doppler frequencies, the system adapts to varying velocity conditions while maintaining a fixed, manageable receiver bandwidth
2Reliability
If the receiver bandwidth is increased to capture heterodyned signals with varying frequencies, then signal information can be preserved, but the system becomes less efficient and more complex
Solution Approach 1:
The system performs preliminary computation and storage of local oscillator waveform samples for a range of expected Doppler frequencies. By pre-computing these waveforms and storing them in memory, the system prepares compensation patterns in advance, allowing rapid selection and application during signal reception without requiring excessive real-time processing bandwidth
Solution Approach 2:
The patent dynamically changes the frequency parameters of the local oscillator based on detected Doppler values. By adjusting the local oscillator frequency to match the received signal's Doppler-shifted frequency, the system maintains reliable signal capture while keeping the receiver bandwidth fixed at a manageable level
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
Enables the LADAR system to accommodate very large Doppler shifts without increasing the receiver bandwidth, ensuring nearly complete overlap of received and LO chirps, and maintaining efficient signal processing across varying Doppler conditions.
Implementation Method 1
velocity differences between a sensor and an object the sensor is evaluating cause large Doppler shifts in a received signal
Implementation Method 2
selecting a portion of the plurality of digital waveform samples using a Doppler value to form an optical heterodyne
Data Source
Figure 1~2A
Figure 2B~2C
Figure 3
AI summary
In one aspect, a method includes representing a range of Doppler frequency offsets as a local oscillator waveform comprising a plurality of digital waveform samples, selecting a portion of the plurality of digital waveform samples using a Doppler value to form an optical heterodyne; and generating a signal associated with a target within a bandwidth of a receiver using the optical heterodyne.