GNSS Receiver AGC Using Pulse Occupancy to Resist Interference
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Solution Overview
Problem
GNSS receivers face challenges in robustly handling pulsed interference from radio navigation systems and radars, particularly in scenarios with high occupancy rates of out-of-band pulses, which can saturate the preamplifier and lead to biased automatic gain control (AGC) and loss of signal tracking.
Innovation Solution
An automatic gain control device for GNSS receivers that estimates the temporal occupancy rate of pulses in the useful band and adjusts gain settings using a non-linear function module, weighting negative and positive deviations to maintain signal amplification and noise estimation accuracy across varying interference scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a preamplifier is used to amplify weak GNSS signals, then the signal amplification is improved, but the preamplifier becomes saturated by powerful pulsed interference from radars and radio navigation systems
Solution Approach 1:
The preamplifier gain is made dynamically adjustable through the AGC system. The gain control signal is adjusted in real-time based on the detected signal conditions, allowing the preamplifier to operate at optimal gain levels that prevent saturation from pulsed interference while maintaining adequate amplification of weak GNSS signals.
Solution Approach 2:
The system changes the operating parameters of the preamplifier by adjusting its gain level. The AGC detector monitors the RF signal characteristics and modifies the preamplifier gain parameter accordingly, transitioning between high-gain mode for weak signals and low-gain mode to avoid saturation from interference.
2Reliability
If the AGC gain control signal is adjusted to prevent preamplifier saturation, then the robustness against pulsed interference is improved, but the amplification of weak GNSS signals deteriorates
Solution Approach 1:
The AGC system dynamically adjusts the gain control signal based on real-time detection of signal conditions. When pulsed interference is detected, the gain is reduced temporarily to prevent saturation, while during normal conditions, the gain is optimized for weak GNSS signal amplification, thus achieving both robustness and sensitivity.
Solution Approach 2:
The AGC detector continuously monitors the RF signal in periodic intervals, detecting the presence of pulsed interference and adjusting the gain control signal accordingly. This periodic detection and adjustment mechanism allows the system to maintain reliability during interference while preserving signal amplification capability during normal operation.
3Measurement precision
If the RF signal level is increased to improve the signal-to-noise ratio, then the correlation function performance is improved, but the occupancy rate of pulsed interference increases
Solution Approach 1:
The system optimizes the RF signal level parameter by adjusting the preamplifier gain to an optimal value that achieves sufficient signal-to-noise ratio for correlation processing without excessively increasing the absolute signal level that would amplify pulsed interference occupancy.
4Object-affected harmful factors
If a blanking technique is used to eliminate interfering signals, then the protection against disturbances is improved, but the useful signal is eliminated along with the interfering signal in high occupancy scenarios
Solution Approach 1:
Instead of blanking the entire signal, the system extracts and removes only the interfering components while preserving the useful GNSS signals. The AGC detector identifies pulsed interference characteristics and selectively attenuates only those frequency-time components that match the interference profile, leaving the continuous GNSS signals intact.
Solution Approach 2:
The AGC detector acts as an intermediary between the RF signal and the correlation processor. It analyzes the signal characteristics and applies selective gain control to suppress interference while preserving useful signals, serving as a smart mediator that makes discrimination-based decisions rather than blanket suppression.
Data Source
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AI summary
Automatic gain control device for satellite positioning receiver characterized in that it includes means for estimating the temporal occupancy rate of pulses in the useful band, a servo control of the automatic gain being optimally performed as a function of said temporal occupancy rate, so as to reduce the influence of pulsed interference in and out of band; in particular, a CAG decision module (6004) provides a control signal to a non-linear function module (6006) applying a determined weighting to the signals resulting from a comparison between the power or amplitude of digitized input signals, and a CCAG setpoint threshold value (6005).