Quasi-Synchronous LDM Demodulation via Sequential FFT Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In quasi-synchronous layered division multiplexing (LDM), the orthogonal relationship between subcarriers is broken due to different numbers of Fast Fourier Transform (FFT) points used for the upper and lower layers, making demodulation challenging, and existing methods fail to specifically disclose a demodulation method.
Innovation Solution
A data transmission system is configured with a transmission device that generates modulated signals using Inverse Fast Fourier Transform (IFFT) processing for both layers with different numbers of points and adjusts their timing to match, and a reception device performs FFT processing to reproduce the data, estimating transmission path characteristics for error correction and demodulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If different numbers of FFT points are used for UL and LL in quasi-synchronous LDM, then the bit rate of LL is improved and delay time tolerances are made identical, but the orthogonal relationship between subcarriers is broken making demodulation difficult
Solution Approach 1:
The patent segments the demodulation process into two distinct stages: first performing FFT with the first number of points to extract UL data, then performing FFT with the second number of points to extract LL data. This segmentation allows each layer to be processed with its optimal FFT size without interfering with the orthogonality requirements of the other layer.
Solution Approach 2:
The patent dynamically adjusts the FFT processing parameters based on the layer being demodulated. The reception device selectively applies different FFT point numbers (first number for UL, second number for LL) depending on which layer's data is being extracted, enabling flexible adaptation to the different requirements of each layer while maintaining demodulation capability.
2Reliability
If the same FFT time window is provided for both UL and LL, then the orthogonal relationship is maintained, but different numbers of FFT points are required for each layer
Solution Approach 1:
The patent resolves the contradiction by operating in the time domain rather than attempting to maintain orthogonality in the frequency domain. By performing sequential FFT operations with different point numbers on the time-domain signal, the system achieves both different FFT sizes for each layer while avoiding the orthogonality constraints that would apply if both layers used the same FFT size simultaneously in the frequency domain.
Data Source
AI summary
[Problem] To propose a technology capable of appropriately demodulating, in a receiving device, a plurality of pieces of data multiplexed through the quasi-synchronous LDM method. [Solution] A transmission device generates a UL modulated signal by using an IFFT process of NUL points, generates an LL modulated signal by using an IFFT process of NLL points different from the NUL points, and transmits signals obtained by timing-adjusting the modulated signals such that the start timings thereof coincide with each other in a predetermined cycle, and combining the timing-adjusted signals at a predetermined power ratio. In addition, the receiving device performs an NUL point FFT process on the reception signal from the transmitting device, reproduces UL and generates UL reception replica, on the basis of the result, and performs an NLL point FFT process on a signal obtained by subtracting the UL reception replica from the reception signal, and reproduces LL on the basis of the result.