Spread Spectrum Signal Detection Using Accumulated Cross Product
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Solution Overview
Problem
In ad-hoc wireless communication systems, particularly in military contexts, detecting and synchronizing with spread spectrum signals from moving nodes is challenging due to high pseudonoise code rates and Doppler shifts, especially for nodes with low-cost oscillators and imperfect clocks, which complicates node discovery and network formation.
Innovation Solution
A system and method for detecting the presence and frequency offset of a spread spectrum radio frequency signal, using a composite PN code and a multilayered PN code structure, along with an Accumulated Cross Product (ACP) search engine, to efficiently search for and synchronize with transmission bursts despite Doppler shifts and clock inaccuracies, enabling reliable node discovery and network formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spread spectrum encoding is used with high processing gain to spread transmitter power over large bandwidth, then detection by unauthorized users becomes difficult, but synchronization accuracy requirements increase significantly
Solution Approach 1:
The patent applies preliminary action by transmitting a long preamble sequence before the actual data transmission. This preamble contains known patterns that allow the receiver to perform correlation-based synchronization in advance, establishing accurate timing and frequency references before the secure data transmission begins. The preamble acts as a preparation phase that resolves synchronization requirements before the main communication occurs.
Solution Approach 2:
The patent uses an intermediary approach by introducing a separate synchronization preamble sequence that mediates between the transmitter and receiver before actual data transmission. This preamble serves as an intermediary signal that carries synchronization information without carrying the actual secret message, allowing the receiver to achieve precise synchronization without compromising the security of the main data transmission.
2Difficulty of detecting and measuring
If very stable oscillators and clocks are used to generate carrier frequency and pseudonoise code, then synchronization difficulty is reduced, but system cost and complexity increase
Solution Approach 1:
The patent applies copying by having the receiver generate a local copy of the pseudonoise code and preamble sequence that matches the transmitted signal. By creating an identical local reference copy, the receiver can perform correlation detection to achieve synchronization without requiring extremely stable oscillators. The local copy serves as a template for matching the received signal, making synchronization achievable with standard frequency tolerances.
Solution Approach 2:
The patent uses parameter changes by allowing the receiver to adjust frequency and phase parameters dynamically during the correlation process. Instead of requiring fixed, ultra-stable oscillators, the system changes the frequency and phase parameters of the local pseudonoise code to match the received signal characteristics. This adaptive parameter adjustment enables synchronization with conventional oscillators that have standard stability specifications.
3Measurement precision
If correlation is performed over very long intervals spanning many symbols and thousands of chips, then spread spectrum transmission detection improves, but processing time and computational load increase
Solution Approach 1:
The patent applies segmentation by dividing the long correlation interval into smaller sub-intervals or blocks. Instead of performing one extremely long correlation operation, the receiver performs multiple shorter correlation operations on segmented portions of the signal. This segmentation reduces the computational burden of each individual operation while maintaining overall detection precision through accumulation of results from multiple segments.
Solution Approach 2:
The patent uses periodic action by performing correlation operations periodically over successive preamble sequences or signal blocks. Rather than requiring one continuously long correlation interval, the system performs repeated correlation operations at periodic intervals, accumulating detection evidence over time. This periodic approach maintains detection precision while reducing the time required for each individual processing step.
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
The solution allows for effective detection and synchronization of spread spectrum signals from fast-moving nodes with low-cost oscillators, reducing the complexity and computational requirements of the receiver, and ensuring reliable node discovery and network formation even under conditions of high Doppler shifts and imperfect clocks.
Implementation Method 1
determine a frequency offset between the spread spectrum radio frequency signal and a receiver frequency reference
Data Source
AI summary
A system and method for detecting a presence and frequency offset of a spread spectrum radio frequency signal is disclosed. The method comprises receiving the spread spectrum radio signal. The signal can be sampled to form a plurality of signal samples. Each signal sample can be multiplied by a complex conjugate of a proximate signal sample to form a plurality of signal sample pairs. The signal sample pairs can be summed over a predetermined dwell time period to form a data vector having a magnitude and angle offset to enable detection of the signal and to enable a frequency offset between the spread spectrum radio frequency signal and a receiver frequency reference to be determined.