N-Dimensional Accumulator for DS-CDMA Alignment Testing
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Solution Overview
Problem
Existing DS-CDMA systems face challenges in quickly and efficiently identifying the transmitted spread code sequence offset alignment and offset time dependence, especially in the presence of a Doppler shift.
Innovation Solution
The method involves transmitting a spread code comprising a data sequence and a pseudo-noise sequence, receiving the spread code at successive clock cycles, and assigning each alignment to an N-dimensional alignment vector. Moving averages are accumulated for each dimension, and the alignment vector that aligns the receiver to the spread code is determined when the sign of each dimension becomes stable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional scalar accumulators are used to test multiple alignments, then the system can identify spread code alignment, but the computational intensity and time required increase significantly
Solution Approach 1:
The patent merges multiple scalar accumulators into a single N-dimensional accumulator that simultaneously tests 2^N alignments. Each dimension of the accumulator corresponds to a bit in the alignment vector, allowing parallel evaluation of multiple hypotheses about spread code timing offset without requiring separate correlation computations for each alignment.
Solution Approach 2:
The invention transforms the alignment testing problem from a one-dimensional scalar accumulation approach to an N-dimensional vector space. By representing alignment hypotheses as N-dimensional binary vectors and accumulating signal values across multiple dimensions simultaneously, the system achieves efficient parallel testing of multiple alignments through a single correlated accumulation operation.
2Reliability
If longer spreading codes are used, then security and low cross correlation improve, but acquisition time increases
Solution Approach 1:
The system performs preliminary alignment testing by accumulating signal values across multiple dimensions before final alignment is achieved. The N-dimensional accumulator continuously evaluates multiple timing hypotheses simultaneously, allowing the receiver to quickly identify the correct alignment even for long spreading codes by parallel processing rather than sequential search.
Solution Approach 2:
The alignment testing process is made dynamic through continuous accumulation and real-time evaluation of multiple hypotheses. The N-dimensional accumulator dynamically updates alignment probabilities as signal is received, allowing the system to adaptively identify the correct alignment without requiring sequential testing of all possible phases, thus reducing acquisition time for long codes.
Data Source
AI summary
A method for correlating using an N-dimensional accumulator to test 2N alignments. The method comprises transmitting a spread code comprising a data sequence and a pseudo-noise sequence; receiving, at a plurality of successive clock cycles, the spread code further comprising a plurality of alignments; assigning each of the plurality of alignments to an alignment vector comprising “N” dimensions; generating a binary representation of each of the plurality of alignments in the alignment vector, wherein 1 and −1 to depict the logic states 0 and 1 with the DS-CDMA signal that has been received by the receiver; accumulating a plurality of moving averages for each dimension of the N-dimensional alignment vector; determining an absolute value of each moving average; combining each of the plurality of moving averages with each corresponding alignment vectors; identifying when the sign of each dimension of the accumulation vector becomes stable; and determining the alignment vector.