Cyclic Delay Precoder for Wireless Signal Diversity
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Solution Overview
Problem
Current cellular wireless communication systems face challenges in maintaining high signal-to-noise ratios due to Rayleigh fading and multipath reception, particularly in high mobility scenarios, where existing diversity schemes struggle to provide reliable bit or packet error performance across varying propagation delays and scattering environments.
Innovation Solution
The implementation of an improved open-loop precoder for both large and small delay CDD diversity schemes, using a matrix-based approach to precode modulation symbols for transmission across multiple antennas, with codeword cycling for enhanced reliability and diversity gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diversity schemes are used to combat fast fading, then bit error reliability is improved, but device complexity increases
Solution Approach 1:
The patent applies parameter changes by transforming spatial diversity parameters into frequency diversity parameters through cyclic delay precoding. The cyclic delay values are carefully selected to create frequency-selective fading patterns that provide diversity gain without requiring complex receiver processing. This parameter transformation resolves the contradiction by achieving reliability improvement through frequency domain manipulation rather than complex spatial processing.
Solution Approach 2:
The patent transitions from spatial diversity (multiple antennas in space) to frequency diversity (multiple subcarriers in frequency) by applying cyclic delay precoding in the frequency domain. This dimensional transformation allows the system to achieve diversity gain by spreading signals across different frequency subcarriers rather than relying solely on spatial separation, thereby improving reliability while maintaining manageable device complexity.
2Reliability
If cyclic delay diversity is applied to transform spatial diversity into frequency diversity, then reliability under multipath fading is improved, but the system requires precise control of delay parameters
Solution Approach 1:
The patent employs parameter changes by establishing specific relationships between cyclic delay values and subcarrier spacing. The delay parameters are designed to create predictable frequency diversity patterns that automatically adapt to multipath conditions. This systematic parameter design simplifies control while achieving improved reliability under multipath fading by transforming spatial characteristics into frequency-domain diversity.
Solution Approach 2:
The cyclic delay diversity scheme operates in an open-loop manner where the transmitter autonomously applies predetermined delay patterns without requiring feedback from the receiver. The system self-adjusts by using fixed cyclic delay values that create frequency diversity patterns inherently suited for multipath environments, eliminating the need for complex closed-loop control mechanisms.
3Reliability
If codeword cycling is implemented for enhanced diversity gain, then bit error reliability is improved, but processing time increases
Solution Approach 1:
The patent implements periodic action through codeword cycling, where different codewords are systematically applied to different subcarrier groups in a repeating pattern. This periodic application of diversity codewords across frequency subcarriers provides enhanced bit error reliability through diversity gain while maintaining efficient processing by using regular, predictable cycles rather than complex adaptive algorithms.
Data Source
AI summary
Several open-loop solutions encompass the small delay CDD codeword cycling and codeword cycling between different re-transmissions of both small and large delay CDD, and include an open-loop codeword cycling method for an SFBC+FSTD scheme, as well as its extension to SFBC+FSTD based HARQ. In one method, a plurality of information bits are encoded, scrambled and modulated to generate a plurality of modulation symbols. The plurality of modulation symbols are mapped onto the subcarriers in at least one transmission layer of a transmission resource. The modulation symbols are then precoded using a matrix for cyclic delay diversity and a set of codewords from a certain codebook to generate a plurality of precoded symbols. The codewords are cycled for every a certain number of subcarriers. Finally, the precoded symbols are transmitted via a plurality of transmission antennas.