Digital Filter Coefficient Inversion for Shorter FBMC/OQAM Filters
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Solution Overview
Problem
Current filter-bank multicarrier communication systems, particularly OFDM, face challenges in spectral efficiency, robustness against channel impairments, and mobility due to poor time and frequency localization, leading to high out-of-band power leakage and sensitivity to Doppler shifts, which are exacerbated by the complexity of prototype filters in 5G scenarios.
Innovation Solution
A method for designing digital filters with a target overlapping factor, involving selecting a candidate filter design satisfying the Nyquist criterion, inverting and truncating its coefficients to achieve a specified signal-to-interference ratio, resulting in shorter filters with improved time and frequency localization, reduced latency, and lower hardware complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional OFDM or FBMC with long prototype filters is used, then orthogonality and spectral separation are maintained, but time and frequency localization deteriorate, leading to high out-of-band power leakage and sensitivity to Doppler shifts
Solution Approach 1:
The patent applies parameter changes by transforming the filter design from time-domain coefficients to frequency-domain coefficients through FFT operation. This parameter transformation enables precise control over spectral characteristics while maintaining orthogonality, thereby reducing out-of-band power leakage without sacrificing reliability.
2Reliability
If long prototype filters are used to maintain orthogonality, then spectral separation is improved, but filter complexity and hardware requirements increase
Solution Approach 1:
The patent replaces the traditional time-domain filter implementation with a frequency-domain filtering approach using FFT-based coefficient generation. This substitution reduces computational complexity and hardware requirements while maintaining the spectral separation performance, as frequency-domain operations are more efficient for this application.
3Productivity
If FBMC with filter-bank is used to improve spectral efficiency, then time and frequency localization is improved, but implementation complexity increases due to additional filtering stages
Solution Approach 1:
The patent creates a universal filter design methodology that can be applied to both OFDM and FBMC systems. The frequency-domain coefficient generation approach serves multiple functions: it maintains orthogonality, enables flexible filter length selection, and works with different modulation schemes, thereby reducing overall system complexity while preserving spectral efficiency gains.
4Measurement precision
If prototype filters with high overlapping factor are used, then time localization is improved, but filter length increases, affecting latency and processing speed
Solution Approach 1:
The patent introduces dynamic flexibility in filter design by allowing the overlapping factor and filter length to be independently optimized based on specific application requirements. The frequency-domain coefficient generation enables adaptive adjustment of these parameters, allowing the system to achieve good time localization when needed while minimizing latency in other scenarios, making the system dynamically adaptable to different operational conditions.
Data Source
AI summary
A method of designing a digital filter for example for use in an FBMC/OQAM telecommunications system, with a target overlapping factor and meeting a specified signal to interference ratio is described, whereby a candidate filter design defined by an impulse response, satisfying the Nyquist criterion and having an overlapping factor higher than the target is selected, and the time and frequency coefficients of its impulse response inverted to define a new filter design; andtruncating the impulse response defining said new filter design to the minimum number of coefficients achieving said specified signal to interference ratio.