OFDM Symbol Mapping Across Sub-Channels for Time-Frequency Diversity
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Solution Overview
Problem
Existing digital communication systems, particularly those using orthogonal frequency division multiplexing (OFDM), face performance limitations due to time and frequency correlations in multi-path channels, which lead to error bursts and loss of orthogonality between sub-carriers, reducing the diversity effect and increasing binary error rates.
Innovation Solution
A method of mapping interleaved data symbols into sub-channels of varying sizes, determined by evaluating symbol interleaving pattern diversity, to maximize time-frequency diversity and combat correlation effects, ensuring optimal interleaving and mapping combinations that enhance system capacity and reception performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data symbols are interleaved and mapped into sub-channels using conventional methods, then the system can handle multi-user access and provide basic diversity, but time-frequency diversity is insufficient and correlation effects in multi-path channels reduce reception performance
Solution Approach 1:
The patent implements dynamic sub-channel allocation where the mapping of interleaved data symbols to sub-channels varies across different time slots and frequency bands. This dynamic mapping ensures that symbols experience diverse time-frequency conditions, maximizing diversity gain and reducing correlation effects in multi-path channels, thereby improving reception performance
Solution Approach 2:
The patent extends the diversity mechanism by distributing data symbols across multiple dimensions including time slots, frequency sub-channels, and spatial layers. This multi-dimensional distribution ensures that no single correlation effect dominates, providing robust reception performance through diversified signal paths
2Reliability
If sub-channels are allocated to maximize diversity, then reception performance improves, but system complexity increases due to evaluation and optimization requirements
Solution Approach 1:
The patent pre-calculates and stores optimal mapping patterns for different channel conditions and system configurations. The mapping module selects from these pre-computed patterns based on current conditions, avoiding real-time complex optimization calculations while maintaining high reception performance through diversity maximization
3Reliability
If interleaving block size is increased to improve diversity, then time-frequency diversity increases, but processing delay increases
Solution Approach 1:
The patent divides the interleaving process into multiple smaller blocks that are processed in parallel across different time slots and frequency sub-channels. This segmentation maintains the diversity benefits of larger interleaving blocks while reducing the processing delay through concurrent operations and pipelined implementation
Data Source
AI summary
A method is provided for mapping data symbols at the input of a multi-carrier modulator, which data symbols are interleaved in blocks of K symbols, into sub-channels of size equal to NSDC consecutive carriers scattered to one or more multi-carrier symbols, NSDC being a sub-multiple of K. The size NSDC of the sub-channels is determined as a function of a symbol interleaving pattern diversity between sub-channels.