Optical Downconversion with Chipping Codes for Signal Isolation
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Solution Overview
Problem
Current communication systems face challenges in processing gigahertz signals due to the high sampling rates required, leading to costly and complex systems, and existing downconversion methods result in signal overlap and interference in lower frequency ranges, making it difficult to isolate signals of interest.
Innovation Solution
A system comprising a controller, signal generator, optical source, dual-drive Mach-Zehnder modulator, photodetector, and dechipping/image rejector is used to downconvert high frequency subbands to a lower frequency range, where the local oscillator tones are encoded with chipping frequencies or codes to isolate specific subbands while suppressing others.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple local oscillators are used to downconvert multiple high frequency subbands to a lower frequency range, then the frequency range coverage is improved, but signal overlap and interference occur making it difficult to separate signals of interest
Solution Approach 1:
The patent segments the downconverted signal by applying unique chipping codes to each local oscillator tone. This allows the composite signal containing multiple subbands to be segmented back into individual subbands through correlation processing with the respective chipping codes, resolving the signal separation difficulty while maintaining broad frequency coverage
Solution Approach 2:
The patent introduces chipping codes as an intermediary mechanism between the local oscillators and the signal separation process. These codes act as unique identifiers for each subband, enabling the receiver to selectively recover individual subbands from the combined downconverted signal without direct interference between them
2Measurement precision
If direct sampling of gigahertz signals is performed, then signal fidelity is maintained, but the sampling rate requirement becomes prohibitively high and costly
Solution Approach 1:
The patent performs preliminary downconversion of gigahertz signals to lower intermediate frequencies before sampling. By first translating the high frequency signals to lower frequencies using local oscillators with chipping codes, the system can then sample at manageable rates while preserving signal fidelity through the reversible nature of the coded downconversion process
Solution Approach 2:
The patent replaces the direct high-speed sampling mechanism with an optical-based downconversion mechanism. Instead of using extremely fast electrical samplers, the system uses optical modulation and detection with Mach-Zehnder modulators and photodetectors to achieve frequency translation, substituting mechanical/electrical sampling with optical processing
3Speed
If bandwidth compression or folding is used to translate multiple signal blocks to a lower frequency range, then the frequency translation is achieved, but signal overlap occurs interfering with signal isolation
Solution Approach 1:
The patent applies local quality by assigning unique chipping codes to each local oscillator tone used in the folding process. This means that while multiple subbands are folded to the same frequency range, each subband maintains its unique coded signature, allowing selective recovery of individual subbands without interference from others, thus preserving signal isolation capability
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 allows for effective isolation of signals of interest in high frequency subbands without modifying existing transmitters, reducing system complexity and cost, and overcoming the limitations of signal overlap in lower frequency ranges.
Implementation Method 1
The first modulator receives a signal from a source and modulates it onto the optical signal propagating through the first arm to form a first modulated optical signal. The second modulator receives the shifted local oscillator tones and modulates them onto the optical signal propagating through the second arm
Implementation Method 2
The DDMZM outputs a signal which is a combination of the first and second modulated optical signals to the photodetector which generates a corresponding electrical signal
Data Source
AI summary
Methods and apparatuses for downconverting high frequency subbands to a lower frequency band and recovering signals-of-interest. The system includes a controller, a signal generator, an optical source, a dual-drive mach zehnder modulator (DDMZM), a photodetector, and a dechipping/image (DI) rejector. The controller outputs chipping frequencies to the signal generator which generates local oscillator (LO) tones shifted by the respective chipping frequencies. The optical source outputs an optical signal to the DDMZM which has first and second arms and modulators. The first modulator receives a signal from a source and modulates it onto the optical signal propagating through the first arm to form a first modulated optical signal. The second modulator receives the shifted local oscillator tones and modulates them onto the optical signal propagating through the second arm to form a second modulated optical signal. The DDMZM outputs a signal which is a combination of the first and second modulated optical signals to the photodetector which generates a corresponding electrical signal. The dechipping/image (DI) rejector receives the electrical signal and one of the chipping frequencies and outputs a signal that maximizes signals in one high frequency subband while suppressing signals in other high frequency subbands.