Digital PLL Delay Compensation for Satellite Carrier Estimation
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Solution Overview
Problem
Existing methods for estimating non-energy parameters of signals, such as phase and frequency, in satellite receivers fail to accurately account for numerically controlled oscillator (NCO) control delays, leading to fluctuations and dynamic errors due to mismatched symbol boundaries across satellite channels.
Innovation Solution
A system with a digital Phase Locked Loop (PLL) that includes a delay meter to measure NCO control delays, a controllable loop filter to adjust bandwidth and order, and an estimator unit to analyze signal parameters, allowing for precise estimation of signal phase, frequency, and their derivatives by adjusting transfer coefficients based on measured delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PLL methods are used for signal parameter estimation, then the system structure is simple, but measurement precision deteriorates due to NCO control delays and symbol boundary mismatches
Solution Approach 1:
The delay meter measures NCO control delays in advance, and the control unit adjusts the loop filter transfer coefficients before the delays cause significant estimation errors. This preliminary measurement and adjustment approach prevents accuracy degradation rather than correcting it after the fact.
Solution Approach 2:
The system continuously measures NCO control delays using the delay meter, feeds this information back to the control unit, which then adjusts the loop filter transfer coefficients accordingly. This closed-loop feedback mechanism maintains measurement precision despite varying delays and symbol boundary mismatches.
2Reliability
If the PLL bandwidth is fixed, then the device complexity is low, but reliability deteriorates due to fluctuation and dynamic errors under varying signal conditions
Solution Approach 1:
The loop filter transfer coefficients are made dynamically adjustable rather than fixed. The control unit modifies these coefficients in real-time based on measured NCO control delays and signal conditions, allowing the PLL bandwidth to adapt to varying operational requirements and maintain reliability under diverse conditions.
Solution Approach 2:
The system changes the transfer coefficients of the loop filter as a controllable parameter to adapt the PLL behavior. By modifying these coefficients based on measured delays and signal characteristics, the system achieves variable bandwidth operation that enhances reliability without requiring a completely redesign of the PLL architecture.
3Measurement precision
If NCO control delays are not compensated, then the ease of operation is high, but measurement precision deteriorates due to symbol boundary mismatches across satellite channels
Solution Approach 1:
The delay meter automatically measures NCO control delays without requiring manual intervention or complex external calibration equipment. The control unit then autonomously adjusts the loop filter coefficients based on these measurements, making the compensation process self-service and maintaining ease of operation while improving precision.
Solution Approach 2:
The system replaces manual or mechanical delay compensation methods with an electronic digital approach. The delay meter and control unit use digital signal processing to measure and compensate for NCO control delays, substituting complex mechanical adjustment mechanisms with simpler electronic control that maintains ease of operation.
Data Source
AI summary
Navigation satellite receivers have a large number of channels, where phase discriminators and loop filter of a PLL operate in phase with data bits and control of numerically controlled oscillator (NCO) carried out simultaneously on all channels. Since symbol boundaries for different satellites do not match, there is a variable time delay between the generation of control signals and NCO control time. This delay may be measured by counting a number of samples in the delay interval. A proposed system measures non-energy parameters of the BPSK-signal carrier received in additive mixture with noise when a digital loop filter of PLL controls NCO with a constant or changing in time delay. A control unit controls bandwidth and a LF order by changing transfer coefficients based on analyzing estimated signal parameters and phase tracking error at a PD output.