CSK Signal Demodulation Reduces Correlator Count
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Solution Overview
Problem
Current methods for demodulating and tracking Code Shift Keying (CSK) signals in GNSS navigation receivers require numerous correlators, leading to hardware overhead and energy losses, which are critical disadvantages for SBAS-enabled devices.
Innovation Solution
A method that involves receiving CSK-modulated signals at a plurality of correlators, convolving them with a reference replica for N shifts corresponding to possible code shifts, selecting the shift with the maximum convolution, and adjusting the Delay Locked Loop (DLL) based on the ratio of convolution values for shifts within a predefined threshold, to determine the transmitted symbol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional correlators are applied for Early and Late code positions to enable tracking, then code phase tracking capability is improved, but the number of correlators increases significantly (e.g., 513 correlators for P=8 bits)
Solution Approach 1:
The patent combines the functions of data demodulation and code phase tracking into a unified correlator structure. The same set of correlators processes both the full correlation function for symbol demodulation and the early-late discriminator outputs for tracking, eliminating the need for separate tracking correlators and reducing the total number of correlators from 513 to 256.
Solution Approach 2:
Each correlator in the patent performs multiple functions simultaneously: it calculates correlation values for data demodulation and provides outputs that feed into the early-late discriminator for code phase tracking. This multi-functionality allows a single set of correlators to handle both demodulation and tracking tasks that traditionally required separate hardware resources.
2Measurement precision
If a full set of correlators is used for both demodulation and tracking, then tracking precision is improved, but hardware cost and energy consumption increase
Solution Approach 1:
The patent merges the tracking function into the existing demodulation correlator infrastructure. The early-late discriminator utilizes correlation outputs already computed for demodulation purposes, adding tracking capability without requiring additional correlator hardware or proportional increases in energy consumption.
Solution Approach 2:
The correlator system provides its own tracking functionality by utilizing its existing computational outputs. The same correlation calculations performed for data recovery also generate the necessary inputs for the early-late discriminator, allowing the system to self-service its tracking needs without external additional resources.
3Measurement precision
If correlation function is calculated with half chip increments for tracking, then tracking accuracy is improved, but the number of correlation points increases
Solution Approach 1:
The patent applies different correlation point densities to different functional requirements: full correlation function calculation uses one-chip increments sufficient for demodulation, while the early-late discriminator uses half-chip increments only where needed for tracking precision. This localized approach to correlation point density optimizes tracking accuracy without uniformly increasing complexity across the entire system.
4Device complexity
If single-digit representation is used in memory blocks, then hardware cost is reduced, but noise immunity worsens by 2 dB
Solution Approach 1:
The patent changes the representation parameter in memory blocks from multi-digit to single-digit format, reducing hardware cost and complexity. This parameter change accepts a trade-off in noise immunity, but the overall system design compensates through the efficient reuse of correlation outputs and reduced hardware overhead, achieving a different optimization balance suitable for cost-constrained applications.
Data Source
AI summary
GNSS receiver includes first type correlators and a maximum selecting unit selecting an output from the first type correlators, and with a common control of all the correlators in code delay, carrier phase and carrier frequency; second type correlators with individual control in code delay of each correlator or each sub-group of second type correlators and with common control of all second type correlators in carrier phase and frequency; and a processor. The first type correlators can convolve one quadrature only, and demodulates CSK symbols, the second type correlators calculate discriminator values for CSK-modulated signal DLL, the demodulated data then is used by the processor to produce improved position and velocity.