Combined Digital Filter and Correlator for GPS Signal Processing
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Solution Overview
Problem
RF receivers face challenges in filtering out interfering signals while correlating desired RF signals, particularly in GPS systems where Doppler frequency shifts and interfering satellites complicate the extraction of accurate location data.
Innovation Solution
A combined digital filter and correlator that generates a modified reference code by incorporating digital filter coefficients with the original reference code, allowing for simultaneous filtering and correlation with minimal processing overhead, using techniques such as iterative modification and frequency analysis to reduce interference effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate digital filter and correlator structures are used, then filtering and correlation functions are achieved, but processing complexity and resource requirements increase
Solution Approach 1:
The patent combines the digital filter and correlator into a single integrated structure where the correlator performs both correlation and filtering operations. The filter coefficients are incorporated into the correlator's reference code, allowing simultaneous filtering and correlation using one processing structure instead of two separate ones.
Solution Approach 2:
The correlator is designed to perform multiple functions: traditional correlation operations and digital filtering operations. By making the correlator universal, it can handle both signal correlation and interference filtering tasks, eliminating the need for a separate dedicated filter structure.
2Reliability
If traditional separate filtering and correlation operations are performed, then signal processing is achieved, but processing time and computational resources increase
Solution Approach 1:
The patent merges filtering and correlation operations into a single computational pass. The integrated structure processes the input signal through one set of operations that simultaneously achieve both filtering and correlation, rather than requiring sequential processing through separate structures.
Solution Approach 2:
The filter coefficients are pre-incorporated into the correlator's reference code structure. This preliminary integration means that during signal processing, the filtering operation is already built into the correlation computation, eliminating the need for a separate filtering pass and reducing total processing time.
3Productivity
If digital filter coefficients are incorporated into the reference code, then filtering is achieved with minimal processing overhead, but the reference code structure must be modified
Solution Approach 1:
The patent merges the filter coefficients directly into the reference code by treating them as scaled versions of the reference code elements. This integration allows the correlator to apply filtering through its existing multiplication and accumulation operations without requiring separate filter computation stages.
Solution Approach 2:
The reference code is modified by applying scaling factors derived from the filter coefficients to each reference code element. This parameter transformation allows the integrated structure to perform filtering while maintaining compatibility with the correlator's existing operation mode, requiring only simple multiplicative adjustments to the reference code values.
Data Source
AI summary
The present invention is a combined digital filter and correlator, which is used in a radio frequency (RF) receiver, and takes advantage of common structures used in both digital filters and correlators. Specifically, a digital filter may mix (multiply) digital filter coefficients with samples of a down-converted RF signal, and then sum the resulting products to provide filtered samples of the down-converted RF signal. Similarly, a correlator may mix (multiply) a reference code with the samples of the down-converted RF signal, and then sum the resulting products to provide a correlation of the down-converted RF signal. The present invention combines the digital filter coefficients and the reference code into a modified reference code, which is then mixed with the samples of the down-converted RF signal and summed to provide a filtered correlation of the down-converted RF signal.