Per-Symbol Layer Shifting in DFTS-OFDM for SIC Complexity Reduction
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Solution Overview
Problem
In high-speed wireless communications, per-sample layer shifting in DFTS-OFDM systems leads to extremely high computational complexity for SIC equalization due to the equivalent system no longer being per-layer DFT followed by a per-subcarrier frequency-flat fading channel, making existing equalization methods inefficient.
Innovation Solution
Implementing per-symbol layer shifting for multiple-stream transmission, where codeword-to-layer mapping is fixed within a DFTS-OFDM symbol and only shifted across consecutive symbols, maintaining the same level of computational complexity as without layer shifting while improving error performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If per-sample layer shifting is applied to DFTS-OFDM, then diversity gain is achieved and error performance is improved, but computational complexity for SIC equalization becomes extremely high
Solution Approach 1:
The patent segments the layer shifting operation from a per-sample basis to a per-symbol basis. By fixing the codeword-to-layer mapping within each DFTS-OFDM symbol and only shifting across consecutive symbols, the system maintains diversity gain while avoiding the need for complex per-sample equalization reconstruction and cancellation operations.
Solution Approach 2:
The patent changes the granularity parameter of layer shifting from sample-level to symbol-level. This parameter change transforms the equalization problem from requiring extremely complex per-sample operations to allowing simpler per-symbol equalization, thereby reducing computational complexity while preserving error performance benefits.
2Adaptability or versatility
If per-sample layer shifting is applied, then each code word is transmitted across multiple layers for diversity, but the equivalent system structure changes making equalization extremely complex
Solution Approach 1:
The patent segments the transmission structure by fixing codeword-to-layer mapping within each DFTS-OFDM symbol. This segmentation allows the system to achieve diversity through inter-symbol layer shifting while maintaining a regular intra-symbol structure that preserves the per-layer DFT followed by per-subcarrier frequency-flat fading channel equivalence, thus keeping equalization complexity manageable.
3Reliability
If SIC is used to improve error performance over linear equalization, then decoding reliability increases, but additional computation for signal reconstruction and cancellation is required
Solution Approach 1:
The patent changes the layer shifting granularity from per-sample to per-symbol, which fundamentally simplifies the SIC computation. By maintaining fixed codeword-to-layer mapping within each symbol, the equalization structure remains regular and allows SIC to be performed with standard computational procedures rather than requiring complex per-sample signal reconstruction and cancellation.
Data Source
AI summary
A system, method and node of single-carrier layer shifting for multiple-stream transmission in a network. Per-symbol layer shifting for multiple-stream transmission is implemented using DFTS-OFDM as an access technique. Code word-to-layer mapping is fixed within a DFTS-OFDM symbol and only shifted across consecutive DFTS-OFDM symbols. The method begins by receiving a multiple-stream transmission by a mapping module for transmission. The transmission includes a plurality of subframes and information carrying symbols transmitted on a plurality of layers. A per-symbol layer shifting scheme is then implemented on the transmission where layer shifting is conducted upon each symbol.