Composite Spreading Code Decorrelator for Signal Acquisition
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Solution Overview
Problem
In secure communication systems, the challenge lies in efficiently acquiring a signal with unknown carrier frequency due to Doppler uncertainty, especially in scenarios where multiple code offsets and carrier frequencies need to be examined, which is time and energy consuming, particularly during node discovery in networks with mobile nodes and unsynchronized clocks.
Innovation Solution
A method and decorrelator system that partially despreads a signal using composite spreading codes, involving phase rotation and accumulation across frequency bins, reducing the search space by tying chip and carrier clocks together, thereby minimizing hardware and computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a full search of all carrier frequency bins is performed to acquire a signal with unknown carrier frequency, then signal acquisition reliability is improved, but hardware complexity and energy consumption increase significantly
Solution Approach 1:
The patent segments the composite spreading code into multiple constituent codes (e.g., first constituent code and second constituent code). The signal acquisition process is divided into stages: first despreading with the first constituent code, then phase rotation, then despreading with the second constituent code. This segmentation allows the receiver to process a reduced search space at each stage rather than searching all frequency bins simultaneously, thereby reducing hardware complexity while maintaining acquisition reliability.
2Reliability
If a full search of all carrier frequency bins is performed to acquire a signal with unknown carrier frequency, then signal acquisition reliability is improved, but energy consumption increases significantly
Solution Approach 1:
The patent segments the composite spreading code into multiple constituent codes (e.g., first constituent code and second constituent code). The signal acquisition process is divided into stages: first despreading with the first constituent code, then phase rotation, then despreading with the second constituent code. This segmentation allows the receiver to process a reduced search space at each stage rather than searching all frequency bins simultaneously, thereby reducing energy consumption while maintaining acquisition reliability.
3Reliability
If multiple code offsets and carrier frequencies are examined to ensure reliable signal acquisition, then signal acquisition reliability is improved, but acquisition time increases
Solution Approach 1:
The patent segments the composite spreading code into multiple constituent codes, dividing the acquisition process into stages. Each stage processes a subset of the total search space, allowing parallel processing and reducing the sequential time required to examine all code offsets and carrier frequencies while maintaining reliable signal acquisition.
Solution Approach 2:
The patent performs preliminary despreading with the first constituent code before phase rotation and subsequent processing. This preliminary action reduces the complexity of the remaining search space, enabling faster completion of the full acquisition process across multiple code offsets and carrier frequencies.
4Reliability
If a composite spreading code is used for secure communication, then security is improved, but the complexity of signal acquisition increases
Solution Approach 1:
The patent segments the composite spreading code into multiple constituent codes that can be processed in stages. The receiver first despreads with the first constituent code, performs phase rotation, then despreads with the second constituent code. This segmented approach maintains the security benefits of composite codes while reducing acquisition complexity compared to processing the entire composite code at once.
Solution Approach 2:
The patent performs preliminary despreading with the first constituent code before the main processing stage. This preliminary action simplifies the subsequent processing of the composite code, reducing the overall acquisition complexity while preserving the security properties of the composite spreading code.
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 significantly reduces the hardware and computational burden required for signal acquisition, allowing for faster and more reliable node discovery with reduced probability of intercept and detection, even under conditions of Doppler shifts and unsynchronized clocks.
Implementation Method 1
a first level phase rotator which spins a frequency of an input signal into a particular frequency bin
Data Source
AI summary
A matched filter decorrelator is described for efficiently performing a carrier frequency search while despreading a P/N long code constructed from two or more constituent codes such as codes A, B, C. The received signal is phase rotated into a frequency bin and partially despread, preferably over all but one of the constituent codes. To despread the final constituent code, the partially despread signal is input in parallel into frequency bins, where a phase rotator sets each input to a different bin. The frequency bins are then despread in parallel over the final constituent code, and an energy peak in one accumulator indicates which bin is the carrier frequency. Alternatively, a Fourier transform could be used over each of the frequency bins. By partially despreading prior to division into carrier frequency bins, hardware and computational burden are reduced as compared to prior art decorrelators. The present invention is particularly apt for use with an acquisition burst in a secure network.