Chaotic Spread Spectrum Waveform PAPR Reduction
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Solution Overview
Problem
Chaotic spread spectrum communication systems face limitations due to high peak-to-average power ratio (PAPR) in chaotic spread waveforms, leading to reduced amplifier gain and lower average power output, which affects transmission efficiency and resistance to interference.
Innovation Solution
The system generates a chaotic spreading sequence with a constant power envelope and variable phase angles, allowing for the formation of a constant amplitude zero autocorrelation (CAZAC) waveform, and dynamically adjusts the PAPR in response to operational parameters to optimize transmitter gain and interference resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chaotic spread waveforms are used for communication, then low probability of intercept and detection are achieved, but peak-to-average power ratio increases leading to reduced amplifier gain
Solution Approach 1:
The patent applies parameter changes by modifying the statistical properties of the chaotic spreading sequence. Specifically, it transforms the traditional Gaussian distributed chaotic sequence into a constant modulus sequence with uniformly distributed phase angles. This parameter transformation maintains the low probability of intercept and detection characteristics while reducing the peak-to-average power ratio from approximately 13 dB to 0 dB, thereby resolving the contradiction between reliability and power efficiency.
Solution Approach 2:
The patent implements local quality by maintaining constant amplitude (local consistency) while achieving global randomness through uniformly distributed phase angles. The constant modulus property ensures local signal stability and predictable power characteristics, while the uniformly distributed phases preserve the global random-like properties necessary for low probability of intercept and detection. This local quality approach resolves the contradiction by providing both reliability and power efficiency.
2Reliability
If chaotic spread waveforms are used, then secure communication is achieved, but average power output decreases due to amplifier gain reduction
Solution Approach 1:
The patent changes the amplitude parameter from Gaussian distributed variable amplitude to constant modulus. This parameter change eliminates the need for amplifier gain reduction, allowing the amplifier to operate at maximum efficiency. The constant amplitude property ensures that the full amplifier gain can be utilized, thereby maximizing average power output while maintaining secure communication through uniformly distributed phase angles.
Solution Approach 2:
The patent skips the traditional approach of using Gaussian distributed chaotic sequences with high PAPR. By directly generating constant modulus sequences with uniformly distributed phases, it rushes through the intermediate step of amplifier gain reduction, achieving both secure communication and maximum power output without the conventional trade-off.
3Ease of manufacture
If conventional pseudo-random number generators are used, then digital logic implementation is achieved, but cyclostationary features reduce randomness quality
Solution Approach 1:
The patent changes the distribution parameter of the spreading sequence from cyclostationary (conventional PRNG) to uniformly distributed phases. This parameter change eliminates the cyclostationary features that compromise randomness quality while maintaining digital logic implementability. The uniformly distributed phase angles provide true randomness characteristics without the periodic artifacts inherent in conventional PRNG-based systems.
Solution Approach 2:
The patent copies the desirable properties of analog chaotic sequences (constant modulus, uniform phase distribution) and implements them through digital logic. By digitally generating sequences that replicate the statistical properties of ideal chaotic signals, it achieves both ease of manufacture through digital implementation and high reliability through superior randomness quality.
Data Source
AI summary
A spread spectrum communication system includes a channel encoder configured for modulating a carrier signal with data to form an information signal. A spreading sequence generator is configured for generating a spreading sequence having a phase angle dependent upon a chaotic sequence and contiguously distributed over a predetermined range. The chaotic sequence also has a magnitude which is selectively dependent upon the pseudo-random number or chaotic sequence. The invention also includes a multiplier configured for forming a spread spectrum signal by multiplying the information signal by the spreading sequence. The spreading sequence generator is responsive to a magnitude control signal for controlling the selective dependency of said magnitude. The magnitude can be constant to form a constant amplitude zero autocorrelation signal. Alternatively, the magnitude can be allowed to vary in selectively controlled chaotic or pseudo-random manner to vary a peak to average power ratio.