COFDM DCM Labeling Diversity for AWGN Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current communication systems, such as digital television broadcasting using COFDM dual-subcarrier-modulation, face challenges in effectively receiving signals over AWGN channels due to high peak-to-average-power ratio (PAPR) and interference, which affects signal reliability and range.
Innovation Solution
The system employs labeling diversity by differing the patterns of QAM or APSK symbols in the lower and upper frequency halves of the COFDM signal, with corresponding labeling bits experiencing error in one half corresponding to less error-prone bits in the other half, and uses discrete Fourier transform and maximal-ratio combining to improve signal-to-noise ratio and reduce PAPR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the same pattern is used to label lattice points of QAM symbols transmitted in parallel, then the system is simple to implement, but reception error rate increases due to noise
Solution Approach 1:
The patent applies asymmetry by using different labeling patterns (first and second patterns) for QAM symbols transmitted in parallel channels. Specifically, when one channel experiences fading, the corresponding symbols use a different labeling pattern than the other channel, creating asymmetric labeling that exploits the diversity between channels to improve reception reliability
Solution Approach 2:
The patent changes the labeling pattern parameter based on channel conditions. By selecting between different labeling patterns (e.g., different bit-to-symbol mappings) for different transmission channels, the system adapts to channel variations and improves reception reliability without requiring complex adaptive modulation
2Length of stationary object
If COFDM DCM signals are transmitted to extend reception range, then transmission range increases, but PAPR causes interference and reduces signal reliability
Solution Approach 1:
The patent changes modulation parameters by using different labeling patterns for different subcarrier groups in COFDM DCM signals. This parameter variation allows the system to maintain signal reliability across extended transmission ranges by adapting to channel conditions through diverse labeling schemes
Solution Approach 2:
The patent uses composite signaling by combining multiple QAM symbols with different labeling patterns in parallel channels. This composite approach creates a more robust transmission that maintains reliability over extended ranges by leveraging the diversity between differently-labeled symbol streams
3Reliability
If labeling diversity is applied to QAM symbols in parallel channels, then reception error rate decreases, but the system complexity increases
Solution Approach 1:
The patent applies local quality by using different labeling patterns in different spatial channels (parallel QAM symbol streams). Each channel has a locally optimized labeling pattern suited to its characteristics, creating labeling diversity that improves reliability without requiring global system redesign
Solution Approach 2:
The patent segments the labeling space by dividing QAM symbols into different groups that use different labeling patterns. This segmentation allows independent optimization of each group's labeling, reducing overall system complexity while maintaining reliability through diversity
Data Source
AI summary
Transmitting apparatus and receiving apparatus for communication systems using coded orthogonal frequency-division multiplexed (COFDM) dual-subcarrier modulation (DCM) signals. The same coded data is mapped both to COFDM subcarriers located in the lower-frequency half spectrum of the DCM signal and to COFDM subcarriers located in its upper-frequency half spectrum. The mapping of COFDM subcarriers in those half spectra employ labeling diversity preferred for reception of DCM with less error when accompanied by interfering additive white Gaussian noise (AWGN). In preferred forms of COFDM DCM signal, the quadrature amplitude modulation (QAM) of COFDM subcarriers is Gray mapped to position palindromic lattice-point labels along one of the diagonals of each square QAM constellation.