Frequency-Domain Echo Detection in DVB-T Receivers
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Solution Overview
Problem
DVB-T receivers face distortion issues due to echo signals with delays exceeding the guard interval, making them vulnerable to multi-path channels, especially when the guard interval is too small, which complicates channel estimation and coherent demodulation.
Innovation Solution
A frequency-domain echo detection method is implemented, measuring signal powers of scattered pilot signals before and after interpolation, calculating a signal-to-power ratio, and adjusting the bandwidth of the time-domain Low-Pass Filter to detect and compensate for echo signals with delays beyond the guard interval, thereby preventing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the guard interval is reduced to increase transmission efficiency, then productivity is improved, but reliability deteriorates due to vulnerability to echo signals with delays exceeding the guard interval
Solution Approach 1:
The patent performs preliminary echo detection by comparing scattered pilot signals before and after time-domain interpolation. By detecting echo signals in advance through signal power comparison, the system can identify multi-path interference before it causes demodulation errors, allowing proactive compensation while maintaining a short guard interval for high transmission efficiency
Solution Approach 2:
The patent implements a feedback mechanism where the echo detection result (signal power ratio comparison) feeds back to control the equalizer's echo compensation process. The system continuously monitors scattered pilot signals, detects echo presence through power ratio threshold comparison, and adjusts compensation parameters dynamically, creating a closed-loop system that maintains reliability without requiring a long guard interval
2Reliability
If time-domain interpolation is performed to compensate for channel distortion, then reliability is improved, but device complexity increases due to additional processing requirements
Solution Approach 1:
The patent extracts only the necessary components for echo detection from the full signal processing chain. Instead of complex full-signal analysis, it focuses specifically on scattered pilot signals, comparing their power before and after time-domain interpolation. This extraction approach provides sufficient echo detection capability while minimizing additional processing complexity
Solution Approach 2:
The patent creates a simplified copy of the signal processing path dedicated to echo detection. By duplicating only the essential time-domain interpolation and power measurement functions for scattered pilot signals, the system achieves reliable echo detection without implementing full-signal complex processing, thus balancing reliability improvement with controlled device complexity
Data Source
AI summary
A method, apparatus and computer program for detecting an echo signal including interpolating at least one fast Fourier transformed OFDM signal received in the time-domain, interpolating the at least one signal generated by the time-domain interpolation in the frequency-domain, using a time-domain varying bandwidth low pass filter (LPF), with bandwidth that varies in response to a bandwidth control signal, measuring at least one signal to power ratio between a scattered pilot signal of the at least one signal generated by the time-domain interpolation and another scattered pilot signal of the at least one signal generated by the frequency-domain interpolation, and comparing the signal to power ratio to a threshold value to determine a state of an echo signal, and providing the bandwidth control signal with the determined echo state information to adjust the bandwidth of the time-domain LPF, based on the bandwidth control signal.