Spread Carrier Self-Correcting Codes for Frequency Error Tolerance
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Solution Overview
Problem
Existing Direct Sequence Spread Spectrum (DSSS) systems face challenges in preamble detection due to significant frequency errors, leading to increased sensitivity and overhead in channel throughput, particularly in Phase Shift Keyed (PSK) systems, where current methods either result in long preambles or complicate receiver design.
Innovation Solution
The system interleaves two pseudo-noise sequences to generate a third sequence that aids in frequency measurement and detection, embedding a reference signal within the information-bearing signal to enhance receiver accuracy and tolerance to frequency errors, while maintaining direct sequence capabilities and Code Division Multiple Access (CDMA) aspects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a longer preamble is used to ensure higher probability of detection, then detection reliability is improved, but frequency alignment requirements become more stringent and detection sensitivity increases
Solution Approach 1:
The patent introduces an intermediary reference signal embedded within the preamble that serves as a mediator between the transmitted signal and the receiver's correlation process. This reference signal enables the receiver to accurately measure frequency offset without requiring perfect frequency alignment, thereby resolving the contradiction between detection reliability and frequency alignment precision requirements
Solution Approach 2:
The patent implements feedback mechanisms where the receiver uses the embedded reference signal to estimate frequency offset and feeds this information back to adjust the correlation process. This feedback loop allows the system to maintain detection reliability while reducing the stringency of frequency alignment requirements
2Object-affected harmful factors
If the preamble is divided into many shorter symbols to reduce frequency error sensitivity, then frequency error tolerance is improved, but the preamble length increases and channel throughput decreases
Solution Approach 1:
The patent merges the reference signal function with the data signal function by embedding the reference signal within the preamble structure itself. This merging allows the system to achieve frequency error tolerance without requiring separate reference signals that would increase overhead and reduce channel throughput
Solution Approach 2:
The patent makes the preamble multi-functional by having it simultaneously serve as both the data carrier and the reference signal. This universality allows the same signal structure to provide both information transmission and frequency offset reference, eliminating the need for separate reference signals and maintaining channel throughput while reducing frequency error sensitivity
3Object-affected harmful factors
If Frequency Shift Keying (FSK) modulation is used for the preamble to reduce frequency error susceptibility, then frequency error tolerance is improved, but receiver design complexity increases
Solution Approach 1:
The patent applies local quality by using Phase Shift Keying (PSK) modulation specifically for the preamble portion of the signal, while maintaining PSK for the data portion. This localized application of PSK to the preamble provides frequency error tolerance without requiring the more complex FSK modulation, thereby avoiding increased receiver design complexity
Solution Approach 2:
The patent segments the signal into preamble and data portions, applying different modulation strategies to each segment. The preamble uses PSK with embedded reference signals for frequency offset tolerance, while the data portion uses standard PSK. This segmentation allows frequency error tolerance without requiring FSK, maintaining receiver design simplicity
Data Source
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AI summary
A transmitter interleaves a first pseudo-noise sequence with a second pseudo-noise sequence to provide a third pseudo-noise sequence which is transmitted and received by a receiver. An XOR of the two sequences produces a third, known-valid pseudo-noise sequence. The receiver further correlates the third pseudo-noise sequence to provide a measure of a frequency of the transmitted signal. The receiver further downconverts and filters the received signal to provide a filtered complex signal. A complex multiplier generates a complex multiplication of the filtered complex signal with a delayed version of the filtered complex signal to provide a product. The delayed version of the filtered signal is delayed by a chip period. A correlator correlates the product to provide the measure of frequency. The first sequence or the second sequence is a reference signal embedded within the information-bearing signal to aid the receiver in detection.