NTSC Interference Rejection in ATSC Receivers
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Solution Overview
Problem
Existing methods for rejecting NTSC co-channel interference from ATSC signals face challenges due to carrier offsets, leading to inaccurate filtering and degradation of ATSC signal quality, as notch filters struggle to align with interference sub-carriers and comb filters inadvertently remove wanted signal components.
Innovation Solution
A method and apparatus that involves frequency-shifting the ATSC signal to align with NTSC interference, using a notch filter to remove interference, and then shifting back to the original frequency, with a lock detector ensuring precise interference rejection, including a NTSC carrier acquisition unit and lock detector to accurately locate and filter out NTSC interferences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If notch filters are used to filter out NTSC interference components, then the NTSC interference can be removed, but when carrier offsets exist between NTSC and ATSC signals, the notch filters cannot align with the interference sub-carriers, causing wrong frequency components to be filtered out
Solution Approach 1:
The patent introduces an intermediary frequency-shifting mechanism between the notch filter and the NTSC interference signal. By detecting the actual frequency of NTSC sub-carriers and dynamically adjusting the notch filter's center frequency to match, the system creates a adaptive intermediary that ensures precise alignment despite carrier offsets between NTSC and ATSC transmitters
Solution Approach 2:
The patent transforms the static notch filter into a dynamic system that can adapt its center frequency based on detected NTSC sub-carrier frequencies. The system continuously monitors and adjusts the notch filter parameters to maintain alignment with interference components, making the filtering process dynamic rather than fixed
2Adaptability or versatility
If comb filter is used to filter out interference components, then the filtering can tolerate carrier offsets, but the wider null of the comb filter simultaneously filters out some wanted ATSC signal components
Solution Approach 1:
The patent applies local quality by creating a highly selective narrow null at the specific NTSC interference frequency while maintaining passband integrity for ATSC signals. Instead of using a wide comb filter null that affects multiple frequencies, the system concentrates filtering action locally at the detected interference frequency point
Solution Approach 2:
The patent segments the filtering function into two distinct stages: first detecting and locking onto the specific NTSC sub-carrier frequency, then applying targeted notch filtering only at that identified frequency. This segmentation allows precise interference removal without the need for broad filtering that would affect adjacent ATSC signal components
Data Source
AI summary
A method and apparatus for rejecting an interference signal from an input frequency spectrum. The method includes the steps of receiving the input signal; frequency-shifting the received input signal by a first frequency-shifting amount; and filtering the frequency-shifted input signal to filter out the interference component from the input signal.