GNSS Signal Correlation for Long Indoor Coherent Integration
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Solution Overview
Problem
Current GPS and GNSS receivers face challenges in acquiring and tracking spread spectrum signals indoors due to signal attenuation, requiring longer integration times and increased hardware complexity, which is limited by the stability of the reference clock and modulation methods.
Innovation Solution
A system and method that processes received signals by multiplying coherent carrier signals with local codes to produce sum and difference signals, allowing for extended integration periods without frequency drift issues, and using orthogonal codes derived from a single satellite signal to improve acquisition and tracking efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the integration time is increased to improve sensitivity for indoor signal reception, then the sensitivity is improved, but the search time increases significantly due to the need to search through more frequency and time cells
Solution Approach 1:
The patent segments the acquisition process into two independent searches: a frequency search and a time search. By separating these dimensions, the system can perform the frequency search first to identify candidate frequencies, then perform a reduced time search only at those frequencies, rather than searching all time-frequency cells exhaustively. This segmentation reduces the total search space and time required.
Solution Approach 2:
The patent transforms the two-dimensional search space (frequency × time) into a sequence of one-dimensional searches. Instead of searching all combinations simultaneously, the system first identifies frequencies of interest and then performs time searches only at those frequencies. This dimensional transformation reduces the effective search complexity from O(N×M) to O(N+M) where N is the number of frequency cells and M is the number of time cells.
2Productivity
If parallel correlators are used to reduce search time, then the productivity is improved, but the device complexity increases
Solution Approach 1:
The patent performs a preliminary frequency search to identify candidate frequencies before performing the main time-domain correlation. By pre-filtering the frequency space and only performing full correlation at promising frequencies, the system achieves faster acquisition without requiring parallel hardware correlators. This preliminary action reduces the effective search space for subsequent processing.
3Adaptability or versatility
If the reference clock stability is poor, then the device can be more flexible and adaptable, but the coherent integration period is limited by frequency drift
Solution Approach 1:
The patent extracts the frequency search from the time integration process. By performing frequency estimation and identification as a separate preliminary step, the system can then perform coherent integration without being constrained by reference clock stability. The frequency search identifies candidate frequencies independently, and subsequent time correlation can proceed with longer integration periods since frequency drift during integration is handled through the separated frequency search process.
Data Source
AI summary
A system for processing a received signal having at least one code applied thereto, the received signal having a frequency, the system comprising: first correlator circuitry arranged to correlate the received signal with a first code to provide an output; second correlator circuitry arranged to correlate the received signal with a second code to provide an output, wherein the first code and the second code are different; and processor for processing together the outputs of the first and second correlator circuitry to cancel the frequency.