Spread Spectrum Decoder Using Multi-Phase Filter Sampling
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Solution Overview
Problem
Existing decoding techniques for asynchronous digital signals in direct sequence spread spectrum systems face challenges in accurately decoding signals affected by transmission faults and partial closure of the 'eye' phenomenon, leading to difficulties in adjusting comparator threshold values and recognizing symbol elements.
Innovation Solution
A decoding device comprising multiple finite response filters and a clock circuit that outputs uniformly distributed clock signals, allowing each filter to capture samples at a predetermined phase angle, with an analysis circuit identifying the optimum clock signal for decoding and an additional filter producing an output signal with maximum amplitude for correct symbol identification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single finite response filter is used for decoding, then the device complexity is low, but the measurement precision of symbol elements deteriorates when the eye is partially closed
Solution Approach 1:
The decoding device is segmented into multiple parallel finite response filters (at least two filters), each processing the input signal independently. This segmentation allows the system to capture different aspects of the partially closed eye signal, improving symbol element recognition accuracy while maintaining manageable device complexity through modular architecture.
Solution Approach 2:
The outputs from multiple finite response filters are merged through a selection mechanism that chooses the optimum filter output based on signal quality metrics. This merging approach combines the advantages of multiple filter responses to achieve higher measurement precision without requiring all filters to be simultaneously active, thus balancing accuracy with complexity.
2Measurement precision
If comparator threshold values are adjusted to handle partial eye closure, then the symbol recognition accuracy improves, but the ease of operation deteriorates due to complex threshold adjustment
Solution Approach 1:
The system performs self-adjustment by automatically selecting the optimum filter output based on signal quality evaluation. The selection mechanism autonomously determines which filter provides the best signal characteristics, eliminating the need for manual threshold adjustment and simplifying operation while maintaining high symbol recognition accuracy.
Solution Approach 2:
The system incorporates feedback mechanisms that evaluate the quality of filter outputs and use this information to select the optimum signal path. This feedback-driven selection process automatically adapts to varying signal conditions, maintaining accurate symbol recognition without requiring operator intervention for threshold adjustment.
3Productivity
If multiple clock signals with different phases are used, then the productivity of signal sampling improves, but the device complexity increases due to additional clock circuitry
Solution Approach 1:
The clock circuit is designed with multi-functionality, generating multiple phase-shifted clock signals from a single source through a phase distribution network. This universal clock structure serves multiple filters simultaneously, improving sampling efficiency across all filter channels while avoiding the complexity of independent clock circuits for each filter.
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
Enables accurate decoding of digital signals even when the 'eye' is partially closed, allowing for correct symbol recognition with adjustable threshold values and improved robustness against transmission faults.
Implementation Method 1
the finite response filter in the receiver correlates the levels of the symbol elements, for example denoted A'' to K'' that it receives successively on its input, at the levels of the successive symbol elements of one of the two symbols
Data Source
AI summary
The invention relates to a decoding device particularly adapted to decode a digital input signal (E) in a transmission system using direct sequence spread spectrum, this digital input signal (E) being composed of symbols, each symbol representing a bit satisfying a Barker code, and comprising several symbol elements.This device comprises several finite response filters (FLT1 to FLT4) each of which receives the digital input signal (E), a clock circuit (CLK_GEN) outputting clock signals (CLK1 to CLK4) to the filters with a frequency equal to the frequency at which symbol elements are produced and uniformly distributed phase shifts, and an analysis circuit (ANL) designed to identify which of the filters is best tuned to the input signal (E) and to control the clock circuit to make it generated a clock signal (CLK5) optimised for decoding and an analysis circuit.