Orthogonal Code Generation Using Two-Level Autocorrelation Sequences
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Solution Overview
Problem
Existing direct sequence spread spectrum communication systems face limitations in user capacity due to the limited number of orthogonal codes, leading to interference issues in overloaded systems, where the number of users exceeds the spreading factor, and existing methods for generating orthogonal codes result in uniform performance across codes, which is not optimal for practical systems.
Innovation Solution
A method and apparatus for generating a pair of orthogonal sets with diverse spreading factors using a two-level autocorrelation sequence, where binary sequences are obtained and quasi-orthogonal sets are generated to produce orthogonal codes with varying cross-correlation values, allowing for flexible design of processing gain and optimal code selection for overloaded systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a total number of orthogonal codes exceeds the spreading factor (system overloading), then user capacity is improved, but multiple access interference increases
Solution Approach 1:
The patent applies local quality by creating non-uniform cross-correlation values among codes, where certain codes have lower cross-correlation with specific other codes. This allows selective assignment of code pairs with minimal interference to active users, rather than treating all code combinations equally. The non-uniform structure enables better interference management in overloaded conditions.
Solution Approach 2:
The patent changes the parameter distribution of cross-correlation values from uniform to non-uniform. By generating codes with diverse cross-correlation characteristics rather than identical values, the system can exploit parameter diversity to reduce interference. The autocorrelation sequence generation method produces codes with varying correlation properties that can be optimized for specific user pairs.
2Ease of manufacture
If existing scrambling operation is used to generate orthogonal codesets, then code generation is simplified, but all codes obtain similar cross-correlation values resulting in uniform performance
Solution Approach 1:
The patent transforms the uniform parameter distribution (identical cross-correlation values) into a non-uniform distribution (diverse cross-correlation values). This is achieved by using autocorrelation sequences with specific mathematical properties that inherently produce varying correlation characteristics across different code pairs, while still maintaining generation simplicity through algorithmic approaches.
Solution Approach 2:
Instead of starting with uniform codes and trying to differentiate them, the patent inverts the approach by generating codes that inherently possess non-uniform cross-correlation properties from the outset. The autocorrelation sequence method naturally produces diverse code characteristics without requiring additional differentiation steps.
3Ease of manufacture
If existing art addresses spreading factor of form N=2n, then code generation is standardized, but flexibility in processing gain design is limited
Solution Approach 1:
The patent creates a universal code generation method based on autocorrelation sequences that works for any spreading factor value, not just powers of 2. The mathematical framework using autocorrelation properties is applicable across different N values, making the system multi-functional and adaptable to various processing gain requirements while maintaining generation efficiency.
Solution Approach 2:
The patent enables continuous adjustment of the spreading factor parameter N without being constrained to discrete powers-of-2 values. By using autocorrelation sequence methods that work for general N, the system achieves flexible processing gain design while maintaining code generation standardization through a unified mathematical approach.
Data Source
AI summary
A method of generating a pair of orthogonal sets with a spreading factor N for a direct sequence spread spectrum communication system, includes selecting a two-level autocorrelation sequence of a period of N−1, the two-level autocorrelation sequence including elements, each of which includes a value of 1 or 0, and obtaining binary sequences based on the two-level autocorrelation sequence. The method further includes obtaining quasi-orthogonal sets based on the two-level autocorrelation sequence and the binary sequences, and generating the pair of the orthogonal sets based on the quasi-orthogonal sets.