Quasi-Orthogonal Code Generation for Spread Spectrum Systems
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Solution Overview
Problem
Current spread spectrum communication systems face limitations in generating orthogonal codes due to restricted synchronization, especially in non-linear channels and diverse user distributions, leading to multiple-access interference and synchronous errors.
Innovation Solution
A method and apparatus for generating two quasi-orthogonal code sets using a two-level autocorrelation sequence, where indices sets are selected and the sequence is circularly read to produce orthogonal codes with a spreading factor N, resulting in approximately N/3 orthogonal codes per set, ensuring minimal autocorrelation side lobes and cross-correlation at ±1 chip shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional orthogonal code generation methods are used in spread spectrum systems, then code orthogonality is maintained under perfect synchronization, but synchronization errors occur in non-linear channels and diverse geographical distributions leading to multiple-access interference
Solution Approach 1:
The patent transforms the traditional binary autocorrelation sequence into a three-level sequence by mapping binary values to three distinct phases (0, 2π/3, 4π/3). This parameter transformation in the signal domain enables the system to tolerate synchronization errors up to ±1 chip while maintaining orthogonality, directly resolving the contradiction between maintaining reliability under synchronization and reducing multiple-access interference.
2Adaptability or versatility
If orthogonal codes are assigned to users based on limited processing gain, then code assignment is restricted, but the total number of available orthogonal codes is limited by the spreading factor
Solution Approach 1:
The patent divides the traditional single orthogonal code set into multiple code sets (at least two sets), each generated from different binary sequences mapped to three-level sequences. This segmentation allows the system to provide multiple orthogonal codes for the same spreading factor N, increasing code assignment flexibility without requiring larger processing gain, thus resolving the contradiction between adaptability and quantity of codes.
3Stability of the object's composition
If thorough synchronization is maintained to ensure code orthogonality, then user distribution diversity is restricted, but practical synchronization cannot be assured in non-linear channels and diversified geographical distribution
Solution Approach 1:
The patent预先 designs the three-level autocorrelation sequence with inherent tolerance for synchronization errors. By mapping binary sequences to three distinct phases with specific autocorrelation properties, the system creates a cushion against synchronization errors before they occur in practice. This allows users to be distributed diversely without requiring strict synchronization while maintaining code orthogonality, resolving the contradiction between stability and adaptability.
Data Source
AI summary
Provided is a method of generating an orthogonal set in a quasi-synchronous spread spectrum system, the method including selecting a two-level autocorrelation sequence at a sequence selector, selecting a first indices set and a second indices set from the two-level autocorrelation sequence, and generating two quasi-orthogonal sets using the first indices set and the second indices set, at an orthogonal code generator.