Spread-Spectrum Signal Acquisition Using Parallel Correlation and Integration
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Solution Overview
Problem
Conventional GPS receivers face challenges in rapidly detecting weak spread-spectrum signals, especially in low signal-to-noise ratio environments, due to lengthy correlation times and high power consumption, making them impractical for portable devices and indoor applications.
Innovation Solution
The apparatus and method involve generating in-phase and quadrature signals, subsampling, correlation engines for coherent and incoherent integration, and a signal detector to accelerate signal acquisition, achieving high-sensitivity detection at a low clock rate for low-power operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If correlation interval is increased to detect attenuated GPS signal, then sensitivity is improved, but search time increases by factor of N^2
Solution Approach 1:
The patent segments the correlation process into multiple parallel correlators that simultaneously process different code phases and frequencies. Instead of sequentially searching through all 1023 code phases at each frequency (which causes N^2 time increase), the system divides the search space into segments handled by different correlators working in parallel, thereby maintaining sensitivity while reducing overall search time
Solution Approach 2:
The patent introduces a temporal dimension by accumulating correlation results over multiple signal periods (e.g., 10 msec or longer integration times). By correlating across multiple periods and accumulating results, the system achieves enhanced sensitivity for weak signals without requiring longer single-period correlation intervals, thus avoiding the N^2 time penalty
2Productivity
If multiple correlators are used to reduce search time, then productivity is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent merges multiple correlator functions into a unified correlation engine that can dynamically configure the number and type of correlators based on signal conditions. The system combines serial correlators for initial acquisition with parallel correlators for rapid searching, and integrates coherent and incoherent integration paths, thereby achieving high productivity without proportionally increasing overall device complexity
Solution Approach 2:
The patent implements dynamic correlator configuration where the number and operation mode of correlators adapt based on signal strength and acquisition stage. The system transitions from serial to parallel correlator operation as signals are detected, and adjusts integration methods (coherent vs. incoherent) based on signal-to-noise conditions, optimizing productivity while managing complexity through adaptive resource allocation
3Device complexity
If serial correlator is used for signal acquisition, then device complexity is reduced, but signal detection time becomes unreasonably long for weak signals
Solution Approach 1:
The patent applies preliminary action by using serial correlators to perform initial signal detection and coarse acquisition before engaging parallel correlators for fine search and tracking. The serial correlator prepares the system by identifying potential signal candidates, which then triggers more resource-intensive parallel processing only when needed, thereby reducing overall acquisition time for weak signals while maintaining simplicity for strong signal scenarios
Data Source
AI summary
An apparatus for acquiring spread-spectrum signals includes a mixer for generating an in-phase signal and a quadrature signal from the spread-spectrum signal, a decimator for subsampling the in-phase signal and the quadrature signal, a correlation engine for producing an in-phase correlation between the subsampled in-phase signal and a PN code and producing a quadrature correlation between the subsampled quadrature signal and the PN code, a first coherent integrator for accumulating a plurality of in-phase correlations to produce an in-phase coherent integration, a second coherent integrator for accumulating a plurality of quadrature correlations to produce a quadrature coherent integration, an incoherent integrator for accumulating the in-phase coherent integrations and the quadrature coherent integrations to produce an incoherent integration, and a signal detector for checking the presence of the spread-spectrum signal based on the incoherent integration.