Adaptive Digital PLL for Variable-Delay Carrier Phase 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 face challenges due to non-zero transport delays and variable time delays in numerically controlled oscillator (NCO) control, leading to fluctuations and dynamic errors.
Innovation Solution
A system with a controllable digital Phase Locked Loop (PLL) that includes a delay meter to measure NCO control delay, a control unit to adjust the loop filter's bandwidth and order, and an estimator unit to accurately estimate signal phase and its derivatives, using transfer coefficients to minimize errors.
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 transport delays and NCO control delays
Solution Approach 1:
The delay meter measures the NCO control delay in advance, and the control unit adjusts the loop filter parameters before the delay affects the signal parameter estimation. This preliminary measurement and adjustment compensates for the transport delay effects, improving measurement precision without requiring complex compensation algorithms during signal processing
Solution Approach 2:
A delay meter is introduced as an intermediary component to measure the NCO control delay. This intermediary device provides accurate delay information to the control unit, which then adjusts the loop filter parameters accordingly. The delay meter acts as a mediator between the NCO control system and the parameter estimation process, enabling precise compensation for transport delays
2Reliability
If the loop filter 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 bandwidth is made dynamic through the control unit, which automatically adjusts the bandwidth parameter based on real-time delay measurements and signal conditions. This dynamic adaptation allows the system to maintain high reliability under varying signal conditions, transitioning between narrow bandwidth for stability and wide bandwidth for fast tracking as needed
Solution Approach 2:
The control unit implements a feedback mechanism where the measured NCO control delay and signal parameter estimates are continuously monitored. Based on this feedback, the control unit adjusts the loop filter bandwidth to optimize performance. This closed-loop feedback ensures the system adapts to changing conditions, improving reliability without requiring manual intervention
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.