OFDM Inter-Carrier Interference Cancellation via Basis Expansion Model
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Solution Overview
Problem
In Orthogonal Frequency Division Multiplexing (OFDM) systems, inter-carrier interference (ICI) caused by channel variations in high mobility environments leads to complex calculations and errors, as existing methods either ignore ICI or require impractical computational resources for accurate channel estimation.
Innovation Solution
The method employs a Basis Expansion Model (BEM) to decompose time-variant channel taps into basis functions, reducing dimensionality using a sub-space tracking algorithm and iterative Conjugate Gradient method for channel and data estimation, effectively addressing ICI and enabling practical implementation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If accurate channel estimation is performed to eliminate inter-carrier interference (ICI) in high mobility environments, then bit error rate performance is improved, but computational complexity becomes impractical
Solution Approach 1:
The patent segments the channel estimation problem by separating pilot symbols from data symbols in the frequency domain. Pilot symbols are specifically allocated at certain frequency positions to estimate channel characteristics, while data symbols are processed separately. This segmentation allows accurate ICI compensation without requiring complex processing of the entire signal, thus improving bit error rate while managing computational complexity.
Solution Approach 2:
The patent transforms the channel estimation from time domain to frequency domain representation. By changing the domain parameter and using frequency domain equalization with pilot-aided estimation, the computational complexity is reduced while maintaining accurate channel characterization. The frequency domain approach allows efficient calculation of channel frequency response and ICI compensation without the heavy computational burden of time domain processing in high mobility scenarios.
2Device complexity
If inter-carrier interference (ICI) is ignored to simplify calculations, then computational complexity is reduced, but channel estimation accuracy deteriorates
Solution Approach 1:
The patent introduces pilot symbols as an intermediary element to facilitate accurate channel estimation. These known pilot symbols are inserted at specific frequency positions and serve as reference points for estimating the channel frequency response. By using these intermediaries, the system can accurately measure and compensate for ICI effects without requiring complex direct processing of data symbols, thus maintaining estimation accuracy while controlling computational complexity.
Solution Approach 2:
The patent performs preliminary channel estimation using pilot symbols before processing the actual data symbols. The channel frequency response is first estimated from the pilot symbols, and then this pre-computed channel information is used to compensate for ICI in the data symbols. This preliminary action separates the complex estimation task from the data processing task, improving accuracy while managing computational load efficiently.
Data Source
AI summary
A method of estimating a time variant Orthogonal Frequency Division Multiplexing (OFDM) while eliminating Inter-carrier Interference (ICI) is disclosed, where the time variant channel matrix is estimated at channel taps using a Basis Expansion Model (BEM). The BEM method decomposes the time variant channel into a group of basis functions in the frequency domain. Coefficients are estimated using a sub-space tracking algorithm that decreases the dimensions of the coefficient matrix allowing for simpler calculation of the estimated signal. The coefficients matrix is estimated using a conjugate gradient iterative method that may be stopped after 6-8 iterations to arrive at an acceptable estimation. Finally, the transmitted data is estimated, again using the conjugate gradient method iteratively, wherein the conjugate gradient method is stopped after a small number of iterations.