Transmission Characteristic Compensation Device for Residual Distortion
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Solution Overview
Problem
Conventional transmission characteristic compensation apparatuses face challenges in improving compensation accuracy, resulting in residual distortion remaining uncorrected.
Innovation Solution
A transmission characteristic compensation apparatus comprising a reception circuit with a first adaptive compensator and an adaptive compensation coefficient calculator, which includes a known-signal detector, a second adaptive compensator, a tap coefficient initial value calculator, a phase shift compensator, and a tap coefficient calculator, to accurately calculate and set tap coefficients for improved distortion compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional adaptive equalization algorithms (DD-LMS, CMA, LMS) are used to calculate tap coefficients, then the compensation process can be implemented, but compensation accuracy is limited and residual distortion remains uncorrected
Solution Approach 1:
The patent divides the adaptive equalization process into two distinct segments: a training period using known signals to calculate initial tap coefficients, and a data period using decision-directed methods to update coefficients. This segmentation allows each phase to use the most appropriate algorithm for that specific task, improving overall compensation accuracy while reducing residual distortion.
Solution Approach 2:
The patent performs preliminary calculation of tap coefficients during a training period using known signals before processing actual data. This preliminary action establishes accurate initial coefficients that account for channel characteristics, enabling better subsequent compensation and reducing residual distortion in the data period.
2Measurement precision
If decision-directed least mean square (DD-LMS) algorithm is used with a numerically-controlled oscillator in a decision-feedback loop, then phase noise compensation can be attempted, but the algorithm becomes difficult to implement in a circuit
Solution Approach 1:
The patent extracts the phase compensation function into a separate phase rotation unit that operates independently from the main adaptive equalization feedback loop. This extraction simplifies the circuit implementation by removing the need for a numerically-controlled oscillator in the feedback loop, while still providing effective phase noise compensation through the phase rotation unit.
Solution Approach 2:
The patent introduces a phase rotation unit as an intermediary component between the adaptive equalizer and the signal processing pipeline. This intermediary handles phase noise compensation separately, allowing the main equalization loop to focus on amplitude and timing corrections, thereby simplifying overall circuit implementation while maintaining phase compensation capability.
3Measurement precision
If constant modulus algorithm (CMA) is used to update tap coefficients, then amplitude modulation compensation can be achieved, but the method becomes difficult to use when multi-value level of modulation method increases
Solution Approach 1:
The patent changes the fundamental parameter used for tap coefficient calculation from amplitude-based (CMA) to error-based (LMS with known signals). By using the known relationship between transmitted and received known signals, the algorithm can accurately compensate for amplitude modulation while maintaining compatibility with high-order modulation schemes, as it relies on signal presence rather than signal characteristics.
Data Source
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AI summary
A reception circuit (5) includes a first adaptive compensator (7) compensating distortion of a received signal. An adaptive compensation coefficient calculator (6) includes a known-signal detector (8) detecting first and second known-signals from the received signal, a second adaptive compensator (10) compensating distortion of the received signal, a tap coefficient initial value calculator (12) calculating an initial value of a tap coefficient of the second adaptive compensator (10) by comparing the first known-signal with its true value, a first phase shift compensator (14) compensating phase shift of an output of the second adaptive compensator (10) using the second known-signal, and a tap coefficient calculator (16) calculating tap coefficients of the first and second adaptive compensators (7,10) by comparing at least one of the first and second known-signals compensated by the second adaptive compensator (10) and the first phase shift compensator (14) with its true value.