Orthogonal Codeset Segmentation for CDMA Interference Reduction
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Solution Overview
Problem
In CDMA systems, maintaining orthogonality between pilot and traffic signals across cells is challenging due to interference, especially in terrestrial applications where multipath propagation and delay differences disrupt signal alignment, leading to reduced system capacity and increased interference.
Innovation Solution
The development of plural orthogonal codesets with shared common codes, where specific codes are used across cells to minimize correlation between traffic and pilot signals, utilizing column permutations and scrambling sequences to maintain orthogonality and reduce interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If orthogonal codes are used in CDMA systems to reduce interference, then system capacity is improved, but maintaining orthogonality across cells becomes difficult due to multipath propagation and delay differences
Solution Approach 1:
The patent segments the code set into multiple orthogonal codesets, where each codeset contains multiple orthogonal codes. Different codesets are assigned to different cells or sectors, allowing the system to maintain orthogonality within each codeset while enabling code reuse across codesets. This segmentation resolves the contradiction by organizing codes into structured groups that preserve orthogonality properties locally while allowing flexible allocation globally.
Solution Approach 2:
The patent changes the parameter of code assignment by introducing multiple orthogonal codesets with different orthogonality structures. Instead of using a single set of orthogonal codes across all cells, the system varies the codeset parameters (which codes are included, their assignments) across different cells and sectors. This parameter variation allows the system to adapt to multipath conditions and delay differences while maintaining orthogonality within each codeset, thereby resolving the contradiction between capacity and orthogonality maintenance.
2Object-affected harmful factors
If different orthogonal codes are assigned to different cells, then inter-cell interference is reduced, but code reuse efficiency decreases
Solution Approach 1:
The patent segments the overall code space into multiple orthogonal codesets, where each codeset can be reused across different cells and sectors. Within each codeset, codes are assigned orthogonally to minimize interference, but the same codeset can be reused in different locations. This segmentation enables both interference reduction (through orthogonal assignment within codesets) and code reuse (across different codesets and locations), resolving the contradiction between these two objectives.
Solution Approach 2:
The patent creates universal codesets that can serve multiple cells and sectors simultaneously. Each orthogonal codeset is designed to be reusable across different geographic locations and network elements. This multi-functionality allows the same codeset to be deployed universally across the network, reducing inter-cell interference through orthogonal assignment while maximizing code reuse efficiency, thereby resolving the contradiction between interference reduction and code reuse.
3Measurement precision
If pilot codes are reused across cells, then signal alignment is improved, but pilot pollution and interference increase
Solution Approach 1:
The patent segments the code assignment strategy by designating specific codes within specific codesets as pilot codes for specific cells or sectors. Instead of universally reusing the same pilot code across all cells (which causes pilot pollution), the system creates localized pilot assignments within each codeset context. This segmentation allows signal alignment to be maintained within each cell's assigned codeset while preventing widespread pilot pollution, resolving the contradiction between signal alignment and pilot pollution reduction.
Solution Approach 2:
The patent applies local quality by making pilot code assignments specific to each cell or sector context. Each cell receives pilot codes from its assigned codeset, creating locally optimized pilot assignments rather than uniform global assignments. This local quality approach improves signal alignment within each cell while limiting pilot pollution to localized areas only, resolving the contradiction between signal alignment and pilot pollution.
Data Source
AI summary
A first orthogonal codeset, obtainable in various manners, is used in a first cell to provide orthogonal spreading codes for traffic signals originating within the first cell. A second orthogonal code set for use in a second cell is obtained that has at least a first code in common with the first orthogonal code set by selecting any code in the first codeset to be the first common code. The plural orthogonal codesets can be utilized in various ways and in various environments. For example, the plural orthogonal codesets can be used for operation of a user equipment unit in a code division multiple access (CDMA) network.