Composite QPSK Code Power Control for Phase-Accurate Downlinks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing power control systems for satellites face challenges in accurately determining the power levels of QPSK modulated signals due to temperature variations, leading to phase uncertainty and increased user range error, especially when signals are transmitted over long distances through an unstable atmosphere.
Innovation Solution
A method and system that involve obtaining a sample of the composite QPSK signal, separating it into in-phase and quadrature components, phase detecting, and processing to generate peak signals for each navigation data code, with a processor analyzing these signals to determine necessary power correction signals for each code to match commanded power settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ground station monitoring is used to measure composite QPSK signal power, then power control can be implemented, but measurement precision deteriorates due to atmospheric instability and non-linear RF power amplifier effects
Solution Approach 1:
The patent introduces a local oscillator signal as an intermediary reference at the satellite transmitter. This local reference allows direct measurement of code power levels at the transmitter output, eliminating the need to measure through the unstable atmosphere. The local oscillator serves as a mediator that enables accurate power measurement without being affected by atmospheric conditions.
Solution Approach 2:
The patent creates a local copy of the transmitted QPSK signal at the satellite transmitter by using the local oscillator to generate replica signals. These local copies allow direct measurement of power levels without transmitting through the atmosphere. The local copy enables measurement of the signal as it leaves the transmitter, avoiding atmospheric distortion.
2Adaptability or versatility
If multiple satellites transmit at the same frequency, then coverage is improved, but signal interference increases reducing energy-per-bit to noise ratio
Solution Approach 1:
The patent segments the QPSK signal into four distinct navigation data codes (C1, C2, C3, C4) with different power levels. Each code can be independently controlled and measured. This segmentation allows the system to manage multiple satellites by controlling individual code powers, reducing interference between signals from different satellites while maintaining coverage.
3Power
If non-linear RF power amplifier is used in satellite transponder, then power amplification is achieved, but phase uncertainty increases due to AM/PM conversion
Solution Approach 1:
The patent implements a feedback mechanism where the actual measured power levels of the four codes are continuously monitored and compared with desired power levels. The difference (error signal) is fed back to control the power levels of the codes, compensating for phase uncertainties introduced by the non-linear RF power amplifier. This feedback loop maintains phase accuracy despite AM/PM conversion effects.
Data Source
AI summary
A method for controlling code power levels of individual codes of a composite quadrature phase shift keyed (QPSK) signal. The method may involve obtaining a sample of the composite QPSK signal; separating the individual codes from the composite QPSK signal; analyzing the individual codes against corresponding commanded code power settings for the individual codes; and determining a code power correction signal needed for each of the individual codes needed to adjust a code power for each of the individual codes to match their corresponding commanded code power settings.