Nonlinear Trellis Equalization for Satellite Channel Distortion
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Solution Overview
Problem
Existing signal equalization techniques fail to effectively address non-linear distortions in satellite communication channels, particularly in bandwidth-efficient modulation signals, leading to suboptimal performance and increased complexity in trellis-based sequence estimation.
Innovation Solution
The implementation of a trellis-based iterative equalizer using non-linear models, such as Volterra series decomposition, memory polynomial, Wiener, Hammerstein, and lookup table models, within the BCJR algorithm to compute branch metrics and correct non-linear distortions in satellite communication signals, allowing for reduced state trellis soft-input soft-output (SISO) equalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional linear equalization techniques are used, then device complexity is reduced, but non-linear distortions in satellite communication channels cannot be effectively addressed, leading to suboptimal performance
Solution Approach 1:
The patent transforms the equalization problem from the time domain to the frequency domain by applying Fast Fourier Transform (FFT) to convert the received time-domain signal into frequency-domain subcarriers. This parameter transformation enables efficient handling of non-linear distortions through frequency-domain equalization while maintaining computational tractability through iterative refinement of equalization parameters
Solution Approach 2:
The patent segments the equalization process into multiple iterative stages, where each iteration refines the equalization parameters and re-estimates the received signal. This segmentation of the equalization task into discrete iterative steps allows the system to progressively reduce complexity while improving performance, avoiding the need for computationally prohibitive single-stage non-linear equalization
2Reliability
If iterative equalization with non-linear models is implemented, then non-linear distortion correction is improved, but computational complexity increases
Solution Approach 1:
The patent implements periodic iterative equalization where the equalization process repeats multiple times with progressively refined parameters. Each iteration periodically updates the equalization filters and re-estimates signal parameters, achieving effective non-linear distortion correction through repeated application of simpler operations rather than a single complex computation
Solution Approach 2:
The patent substitutes direct time-domain non-linear equalization with frequency-domain processing using FFT-based methods. This mechanical substitution replaces computationally intensive time-domain convolution and non-linear operations with more efficient frequency-domain multiplications and additions, significantly reducing the computational power required while maintaining correction effectiveness
3Measurement precision
If full complexity trellis structure is used, then sequence estimation accuracy is improved, but device complexity and processing time increase exponentially
Solution Approach 1:
The patent segments the trellis structure into multiple smaller sub-trellises corresponding to different frequency-domain subcarriers. Each sub-trellis processes a specific subset of the signal, and the overall sequence estimation is obtained by combining results from all sub-trellises. This segmentation reduces the complexity of each individual trellis while maintaining overall estimation accuracy through cooperative processing
Solution Approach 2:
The patent transitions from time-domain sequence estimation to frequency-domain processing by applying FFT, effectively adding a frequency dimension to the estimation problem. This dimensional transformation allows the use of simpler frequency-domain equalization filters combined with iterative refinement, avoiding the exponential complexity growth associated with full-time-domain trellis structures
4Productivity
If bandwidth-efficient modulation is used, then spectral efficiency is improved, but susceptibility to non-linear distortions increases
Solution Approach 1:
The patent implements iterative feedback equalization where the equalizer output is fed back into the system for re-processing. Each iteration uses the previously equalized signal to refine the equalization parameters and correct residual non-linear distortions. This feedback mechanism allows the system to progressively compensate for non-linear effects that disproportionately affect bandwidth-efficient modulation schemes
Solution Approach 2:
The patent substitutes direct time-domain equalization with frequency-domain processing, replacing the mechanical equalization process with FFT-based frequency-domain filtering. This substitution enables more precise control over the equalization characteristics, allowing the system to effectively counteract non-linear distortions while preserving the spectral efficiency of bandwidth-efficient modulation
Data Source
AI summary
A method includes: generating a trellis; generating one or more predicted symbols using a first non-linear model; computing and saving two or more branch metrics using a priori log-likelihood ratio (LLR) information, a channel observation, and the one or more predicted symbols; if alpha forward recursion has not yet completed, generating alpha forward recursion state metrics using a second non-linear model; if beta backward recursion has not yet completed, generating beta backward recursion state metrics using a third non-linear model; if sigma forward recursion has not yet completed, generating sigma forward recursion state metrics using the branch metrics, the alpha state metrics, and the beta backward recursion state metrics; generating extrinsic information comprising a difference of a posteriori LLR information and the a priori LLR information; computing and feeding back the a priori LLR information; and calculating the a posteriori LLR information.