Code Phase Shift Acquisition Using Segmented PN Sequences
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Solution Overview
Problem
Conventional methods for acquiring code phase shift between pseudo-random (PN) sequences, such as those used in signal processing systems like GNSS, are computationally intensive due to the need for complex multiplications and additions, making them unsuitable for sequences of large lengths, and are sensitive to noise, leading to inaccurate phase shift estimation.
Innovation Solution
A method and device that transform PN sequences into complex phase signals, partition them into smaller groups, and compare these groups to obtain phase coherent indicators, reducing noise sensitivity and computational complexity by using a mapping unit, comparison unit, and calculating unit to determine the code phase shift based on the phase of the indicators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If FFT is used to transform sequences from time domain to frequency domain for cross-correlation computation, then integration computation requirement is eliminated, but computational complexity increases to N·log2N due to complex multiplication and addition
Solution Approach 1:
The patent segments the sequence of length N into multiple subsequences of length M (where M < N). By computing cross-correlation on these smaller subsequences independently and then combining results, the computational complexity is reduced from O(N·log2N) using FFT to O((N/M)·M·log2M) = O(N·log2M), which is significantly lower for large N. This segmentation approach eliminates the need for full-sequence FFT while maintaining cross-correlation accuracy.
2Ease of operation
If conventional cross-correlation computation is performed in time domain using convolution theory, then the method is straightforward, but numerous multiplication and integration computations make it impractical
Solution Approach 1:
The patent replaces the mechanical time-domain convolution process (which requires numerous multiplications and integrations) with a frequency-domain approach applied to segmented subsequences. By transforming each subsequence to frequency domain, performing point-wise multiplication, and inverse transforming, the method maintains conceptual simplicity while dramatically reducing computational burden through the smaller size M compared to full sequence N.
3Quantity of substance
If the length N of the sequence increases to handle large sequence lengths in GNSS or GPS systems, then the system can process more data, but computational load of FFT increases at an even faster rate
Solution Approach 1:
The patent divides the large sequence of length N into multiple smaller subsequences of length M. This allows the system to handle large N (required for GNSS/GPS applications) while keeping the actual computation on small M, where FFT computational load M·log2M remains manageable. The overall computational load becomes (N/M) × (M·log2M) = N·log2M, which scales linearly with N rather than super-linearly as would full-sequence FFT.
Solution Approach 2:
The patent performs cross-correlation computation on partial subsequences rather than the complete sequence at once. By processing each subsequence independently and combining results, the method achieves the necessary processing for large N applications while using only the computational resources needed for smaller M-length operations, thus avoiding the excessive computational load of processing the entire large sequence in one FFT operation.
Data Source
AI summary
A method for acquiring a code phase shift between an input sequence and a reference sequence is provided. The method is to be implemented using an acquisition device that includes a mapping unit configured to transform the input sequence and the reference sequence respectively into an input signal and a reference signal each with a complex phase, a comparison unit configured to compare the input signal with the reference signal so as to obtain a phase coherent indicator, and calculating unit configured to obtain the code phase shift between the input sequence and the reference sequence based on a phase of the phase coherent indicator and a number of bits of the input sequence.