Optical Free Space Data Communication System Digital Synchronization
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Solution Overview
Problem
Current optical free-space data communication systems, particularly for satellite communication, face challenges in achieving high-rate data transmission due to the complexity and limitations of optical phase-locked loops, computational intensity, and reduced spectral efficiency, mainly due to the constraints of analog-to-digital converters and the need for radiation-resistant components.
Innovation Solution
The system employs a dual-modulation approach using a slow and fast signal modulated onto a single carrier, where the slow signal is used to determine signal parameters for demodulating the fast signal, reducing the requirements for analog-to-digital converters and enabling high-rate data transmission with increased spectral efficiency, and utilizes 1-bit and higher-bit transceivers for efficient demodulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical phase-locked loop is used for synchronization, then baseband transformation is achieved, but device complexity increases and frequency offset compensation is limited
Solution Approach 1:
The patent extracts the synchronization function from the traditional optical phase-locked loop and implements it digitally. The received optical signal is converted to electrical signals by photodetectors, and digital signal processing is used to determine phase and frequency differences, replacing the complex analog phase-locked loop circuitry with simpler digital processing blocks.
Solution Approach 2:
The patent replaces the analog/optical phase-locked loop mechanism with a digital processing system. Instead of using analog phase detection and feedback loops, the system uses digital signal processing to analyze the received signal, determine synchronization parameters, and compensate for phase and frequency offsets computationally.
2Measurement precision
If digital signal processing is used to compensate for phase and frequency errors, then synchronization is improved, but computational effort increases
Solution Approach 1:
The patent applies preliminary digital signal processing to the received signal to extract phase and frequency information before main demodulation. By determining the phase and frequency difference early in the processing chain using the extracted in-phase and quadrature components, the system prepares synchronization parameters in advance, reducing the computational burden on subsequent processing stages.
3Measurement precision
If a pilot tone is used for phase noise mitigation, then frequency and phase compensation is achieved, but spectral efficiency decreases
Solution Approach 1:
The patent makes the local oscillator serve multiple functions: it acts as both the mixing signal for coherent detection and the reference for phase and frequency compensation. By using the same local oscillator signal for both purposes, the system eliminates the need for a separate pilot tone, as the local oscillator itself provides the necessary reference information embedded in the mixing process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies the communication system, reduces computational effort, and allows for high-rate data transmission while maintaining high spectral efficiency, using existing transceivers and radiation-resistant components, without the need for phase synchronization or phase-locked loops.
Implementation Method 1
In the coherent receiver, the received signal is superimposed with a local oscillator to transform it into the baseband
Implementation Method 2
The resulting photocurrents are used to control the local oscillator and are simultaneously digitized by transceivers
Data Source
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AI summary
The invention relates to an optical free space data communication system, in particular for optical satellite communication, having a transmitter for generating an optical data signal and a receiver for the optical data signal. The transmitter has a light source for generating a carrier as well as a slow modulator and a fast modulator. The slow modulator modulates a slow signal onto the carrier, and the fast modulator modulates a fast signal onto the carrier. In particular the fast signal has a data signal. The receiver has a local oscillator which is superimposed with the received data signal. Furthermore, the receiver has an analog/digital converter for demodulation of the slow signal, and an evaluation device is connected to the analog/digital converter. The evaluation device is designed to determine signal parameters of the transmission. Furthermore, the receiver has a transceiver for demodulation of the fast signal, the evaluation device being designed so that the signal demodulated by the transceiver is compensated by means of the determined signal parameters.