OFDM Receiver Equalizer Switching via AGC-Based Doppler Estimation
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Solution Overview
Problem
Digital terrestrial broadcasting receivers face challenges in accurately estimating Doppler frequency, especially at low-speed movements, leading to potential errors in reception due to high-speed fading and variations in delay time, which existing technologies struggle to address effectively.
Innovation Solution
An OFDM receiver equipped with a Doppler frequency detector and a Doppler frequency estimating circuit that uses a control signal to generate a Doppler detection signal, allowing for the switching of equalizers based on propagation path conditions, thereby improving reception accuracy by reducing the arithmetic scale and enhancing estimation accuracy even at high-speed movements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Doppler frequency estimation methods are used, then the system can operate with simple equalizer switching, but estimation accuracy deteriorates at low-speed movements leading to reception errors
Solution Approach 1:
The patent uses the AGC control signal as an intermediary to extract Doppler frequency information. Instead of directly estimating Doppler frequency from the received signal, the system extracts frequency components from the AGC control signal which already contains Doppler-induced power variation information, thereby improving estimation accuracy especially at low speeds
Solution Approach 2:
The system performs preliminary AGC processing on the received signal before Doppler frequency estimation. The AGC circuit first normalizes the signal power, and then the Doppler frequency is estimated from the AGC control signal, preparing the data in advance for more accurate frequency extraction
2Measurement precision
If multiple equalizers are switched based on propagation conditions, then reception accuracy improves under high-speed fading, but system complexity increases
Solution Approach 1:
The AGC control signal serves multiple functions: it controls the amplifier gain to maintain constant output power, and simultaneously serves as the source for Doppler frequency estimation. This multi-functionality reduces the need for separate processing circuits and simplifies the overall system architecture
Solution Approach 2:
The system uses feedback from the AGC control signal to determine equalizer switching decisions. The Doppler frequency detector continuously monitors the AGC signal and provides feedback information that triggers appropriate equalizer selection, creating a closed-loop system that adapts to changing propagation conditions
3Productivity
If the arithmetic scale is reduced for faster processing, then system speed improves, but estimation accuracy may deteriorate
Solution Approach 1:
The patent extracts only the essential frequency information from the AGC control signal using frequency component extraction circuits. Instead of performing complex full-signal processing, the system extracts relevant Doppler frequency components directly from the AGC signal, reducing arithmetic operations while maintaining accuracy
Solution Approach 2:
The processing is segmented into distinct functional blocks: AGC control signal generation, frequency component extraction, Doppler frequency detection, and equalizer switching control. This segmentation allows each block to perform its specific function efficiently with minimal computation, improving overall processing speed
Data Source
AI summary
A radiofrequency signal is converted to an intermediate frequency signal by a tuner, which is amplified by a variable gain amplifier. The so-amplified signal is converted into a digital signal by an ADC, which is supplied to an FFT, where it is separated into signals set every carrier, followed by being supplied to equalizers different in characteristic. The digital signal outputted from the ADC is further supplied to a level converting circuit from which a control signal is generated. The control signal is supplied to a DAC and a Doppler frequency detector. The DAC generates a gain control signal and supplies the same to the variable gain amplifier. The Doppler frequency detector outputs a frequency component of the control signal as a Doppler detection signal. The Doppler detection signal is compared with a threshold value by a comparator. A selector selects one of signals outputted from the equalizers, in accordance with a select signal indicative of the result of comparison.