GNSS Correlator Memory Reduction via Bit Extraction
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Solution Overview
Problem
Existing GNSS receiver methods face challenges in achieving high detection rates at a given false alarm rate while minimizing memory requirements, often resulting in reduced detection sensitivity and slow signal acquisition in weak signal conditions.
Innovation Solution
The proposed method employs a correlator with a correlator shift register and evaluator that processes correlation values efficiently, using a combination of integration and correlation phases to reduce memory requirements while maintaining high detection rates, by storing and processing correlation sums in a manner that allows for precise determination of satellite signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If full correlation sums are evaluated for multiple phase positions and Doppler frequencies, then detection rate is improved, but memory requirements increase considerably
Solution Approach 1:
The patent extracts only the most significant bits (MSBs) of the correlation sums for storage and evaluation, discarding the less significant bits (LSBs). This extraction approach maintains the essential detection information while dramatically reducing the memory requirements from storing full-precision correlation sums to storing only the top few bits, thus resolving the contradiction between detection rate and memory requirements
Solution Approach 2:
The patent creates a simplified copy of the correlation sum data by storing only the most significant bits rather than the complete correlation values. This copied representation retains sufficient information for reliable detection while occupying minimal memory space, effectively balancing detection performance with memory constraints
2Quantity of substance
If correlation sums are rescaled or reduced to fit memory constraints, then memory requirements are reduced, but detection sensitivity is lowered
Solution Approach 1:
Instead of rescaling or reducing correlation sums that would lose precision, the patent extracts only the most significant bits that contain the essential detection information. This extraction method preserves detection sensitivity by retaining the dominant signal characteristics while naturally limiting the stored data to fit memory constraints without artificial rescaling
3Quantity of substance
If Tong detector is used to reduce memory requirements, then memory requirements are reduced to 4 bits, but detection rate is considerably reduced
Solution Approach 1:
The patent creates a partial copy of the correlation sum information by storing only the most significant bits (e.g., top 6-8 bits) rather than using a Tong detector that processes all bits through threshold comparisons. This copied representation maintains much better detection performance than Tong detectors while still achieving significant memory reduction, as it preserves the actual correlation magnitude information rather than merely counting threshold exceedances
Data Source
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AI summary
In a GNSS receiver data sequences derived from a digital signal each with an internally generated correlation sequence derived from a basic sequence and mixed with frequency signals corresponding to various Doppler frequencies and in various phase positions with respect to the data sequence are correlated and the correlation values evaluated. In difficult conditions, e.g., RF levels of the signal of -145dBm and less, correlation values produced with the same correlation sequence and phase position but with a plurality of data sequences are evaluated together in that, in an evaluator (49), every correlation value is, in a comparator (52), compared with at least a first value threshold and a second value threshold, with the latter having a value between 1.3 and 1.7 times the value of the first and values -1, 0 or +1 assigned accordingly to a correlation term which is then added to an integer correlation counter which varies over a counter interval, e.g., [0,15], in an adding unit (53). The correlation counters corresponding to the various Doppler frequencies and phase positions are stored in a memory unit (54). In an arbitration unit (51) a correlation indicator is derived from each correlation counter and the latest corresponding correlation value and the six largest correlation indicators selected and stored together with their Doppler frequencies and phase positions.