Inverse Channel Estimation for Repeater Stability
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Solution Overview
Problem
Conventional methods for estimating the inverse channel of a repeater's receiving channel fail to ensure stability and causality due to z-plane poles and zeros located outside the unit circle in real environments.
Innovation Solution
An apparatus and method that estimate the channel using a known signal, generate an inverse minimum phase filter coefficient, and combine it with an inverse group delay filter coefficient to produce a time-domain filter coefficient, ensuring stability and causality by separating the channel into minimum phase and all-pass components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If direct inverse transformation using division is used to generate inverse channel, then the process is simple, but stability and causality cannot be ensured when poles and zeros are outside the unit circle
Solution Approach 1:
The patent segments the channel estimation process into two distinct parts: minimum phase component extraction and all-pass component handling. By separating the channel transfer function H(z) into H_min(z) * H_ap(z), where H_min(z) contains zeros inside the unit circle and H_ap(z) contains the all-pass component with zeros outside the unit circle, the patent enables stable inverse transformation for the minimum phase part while separately processing the all-pass part to maintain causality. This segmentation resolves the contradiction by making the complex process manageable and reliable.
Solution Approach 2:
The patent transforms the channel representation from the original domain to the minimum phase domain through parameter changes. By computing the minimum phase equivalent channel H_min(z) with the same magnitude response but with all zeros moved inside the unit circle, the patent enables stable inverse transformation. The parameter change from general channel coefficients to minimum phase channel coefficients resolves the stability issue while maintaining the essential channel characteristics.
2Ease of operation
If conventional division-based inverse transformation is used, then computation is straightforward, but it fails when z-plane poles and zeros are located outside the unit circle in real environments
Solution Approach 1:
The patent introduces the minimum phase channel H_min(z) as an intermediary between the original channel H(z) and the inverse channel. Instead of directly computing 1/H(z) which fails when poles/zeros are outside the unit circle, the patent uses H_min(z) as a mediator that has the same magnitude response but with all zeros inside the unit circle, enabling stable inverse transformation. This intermediary approach maintains computational feasibility while ensuring accuracy.
3Reliability
If the repeater compensates for distortion using estimated channel, then signal quality improves, but stability and causality are not ensured due to pole-zero locations
Solution Approach 1:
The patent performs preliminary action by pre-computing the minimum phase channel H_min(z) and its inverse before actual signal compensation. By preparing the stable inverse filter coefficients in advance through the minimum phase transformation, the system ensures that the compensation process will be both accurate and stable. This preliminary preparation resolves the contradiction by ensuring reliability while managing complexity through structured preprocessing.
Data Source
AI summary
Provided is an apparatus and method for estimating inverse channel of a repeater's receiving channel, which ensures stability and causality by generating a time-domain filter coefficient having information on an inverse channel of repeater's receiving channel from a signal transmitted from a main transmitter or another repeater. The apparatus includes: a channel estimator for estimating a channel established by a transmission path from a received signal; an inverse minimum phase filter coefficient generator for generating inverse channel of a minimum phase channel from the estimated channel, and converting the inverse channel of the minimum phase channel into a time-domain filter coefficient; an inverse group delay filter coefficient generator for generating a time-domain filter coefficient by using the estimated channel and the minimum phase channel; and a combiner for generating an inverse channel of a receiving channel in a time domain by combining the filter coefficient and the filter coefficient.