Coherent Bandwidth Aggregation for Multipath Bias Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional signal processing systems for guidance and positioning, particularly in multipath or cluttered environments, face challenges in maintaining coherence and accuracy due to multipath bias effects, especially at low grazing angles, which degrades the validity of interferometric processing results.
Innovation Solution
A method involving the transmission of a sequence of pulses with varying center frequencies, coherent summation, and application of a correction term for phase shifts, combined with radar and interferometric post-processing to form precision guidance and tracking data with increased effective bandwidth and reduced multipath bias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherence is maintained between multiple transmitters for extended time integration, then tracking precision is improved, but system complexity and difficulty of maintaining coherence increases
Solution Approach 1:
The patent introduces a reference signal as an intermediary that mediates the coherence relationship between multiple transmitters. Each transmitter is synchronized to the same reference signal, which acts as a common timing and phase reference, simplifying the maintenance of coherence across multiple transmitters without requiring direct pairwise synchronization between all transmitter pairs.
Solution Approach 2:
The system employs feedback mechanisms where the received signals are processed to generate range-Doppler maps that provide information about target position and velocity. This feedback is used to adjust and maintain coherent integration over extended time periods, allowing the system to track moving targets while maintaining precision despite the complexity of multi-transmitter coherence requirements.
2Measurement precision
If bandwidth is increased to improve range resolution, then multipath bias effects are reduced, but system complexity and processing requirements increase
Solution Approach 1:
The patent segments the wide bandwidth into multiple narrower sub-bands, each processed separately to generate individual range-Doppler maps. This segmentation approach allows the system to achieve the benefits of wide bandwidth (improved range resolution and multipath discrimination) while keeping the processing complexity of each individual band manageable. The results from multiple sub-bands are then combined to achieve the full resolution benefit.
Solution Approach 2:
The system transitions from processing signals in a single time dimension to processing in both time and frequency dimensions by utilizing multiple frequency sub-bands. This dimensional expansion allows the system to resolve multipath effects by distinguishing signals based on their frequency-dependent propagation characteristics, achieving superior range resolution without overwhelming processing requirements at any single frequency point.
3Measurement precision
If coherent integration is extended for improved precision, then tracking accuracy is enhanced, but vulnerability to multipath bias effects increases
Solution Approach 1:
The patent exploits the frequency dimension by transmitting signals across multiple frequency sub-bands and processing them separately. Multipath effects exhibit different characteristics across frequencies due to frequency-dependent propagation delays and phase shifts. By analyzing signals in the frequency domain and combining results from multiple sub-bands, the system achieves coherent integration over extended periods while using frequency diversity to discriminate against and reduce the impact of multipath bias effects.
Solution Approach 2:
The system performs preliminary processing of signals from multiple frequency sub-bands before combining them for coherent integration. Range-Doppler maps are generated for each sub-band separately, allowing preliminary identification and weighting of direct-path signals versus multipath signals. This preliminary action prepares the data in a form that enables more effective coherent integration while minimizing the contaminating effect of multipath biases on the final tracking accuracy.
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 enhances the accuracy of guidance and positioning systems by increasing effective range resolution and reducing vulnerability to multipath bias effects, improving the precision of angle estimation and tracking in challenging environments.
Implementation Method 1
radio frequency (RF) receiver on a moving object... range Doppler (RD) map generation... frequency shift and a radial motion phase shift effect
Implementation Method 2
phase difference comparison via radio frequency interferometric (RFI) processing... radio frequency orthogonal interferometry (RF/OI)... performing phase comparisons for each co-registered detection; and performing angle estimation of the position of the one or more objects
Implementation Method 3
forming a complex valued range/Doppler map developed by correlating a received signal with a transmitted signal by matched filtering against a respective transmit key
Data Source
AI summary
A system and method for using coherent aggregated bandwidth over multiple transmissions for improved performance of precision guidance and positioning and of object tracking systems. Angular offset (Az/El) estimations are strongly impacted by interference between direct and (comparable amplitude) ground-reflected signals. In rough ground situations, there could be many ground reflected signals. Bandwidth aggregation as used herein achieves sharper range sidelobes and smaller magnitude multipath interference terms resulting in increasingly accurate interferometric results.