VSB Signal Demodulation Using PN63 Self-Correlation
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Solution Overview
Problem
Digital television (DTV) signals face challenges in maintaining carrier wave synchronization due to pilot signal distortion, particularly in negative frequency ranges, where the pilot signal strength is reduced, leading to degraded performance in estimating frequency and phase offsets.
Innovation Solution
A method and apparatus for estimating a pilot-less carrier wave frequency offset by self-correlating neighboring pseudorandom noise 63 (PN63) signals, compensating for frequency and phase offsets using a frequency and phase locked loop (FPLL) system, and removing the pilot signal from the VSB signal to improve demodulation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pilot signal is used for carrier wave synchronization, then carrier wave recovery is enabled, but frequency offset estimation deteriorates in negative frequency ranges where pilot signal strength is reduced
Solution Approach 1:
The patent introduces a pseudorandom noise (PN) sequence as an intermediary element to assist in frequency offset estimation. The PN sequence is modulated onto the carrier wave along with the data signal, and its known structure allows the receiver to perform correlation-based estimation of frequency offset, providing an additional reference beyond the pilot signal alone, especially useful when pilot signal strength is reduced in negative frequency ranges
Solution Approach 2:
The patent changes the parameter of using a single pilot signal to using multiple reference signals (pilot signal plus PN sequence). By incorporating the PN sequence with specific autocorrelation properties, the system gains improved frequency offset estimation capability across the entire frequency range, including negative frequencies where the pilot signal alone performs poorly
2Productivity
If pilot signal strength is reduced to accommodate other signal components, then bandwidth efficiency improves, but frequency and phase offset estimation performance deteriorates
Solution Approach 1:
The patent segments the reference signal function into two distinct components: the pilot signal for basic carrier recovery and the PN sequence for enhanced frequency and phase offset estimation. This segmentation allows each component to be optimized for its specific function, enabling the system to maintain accurate synchronization even when the pilot signal strength is reduced for bandwidth efficiency
Solution Approach 2:
The patent creates a composite reference signal structure combining the pilot signal and PN sequence. This composite approach leverages the strengths of both signals - the pilot signal provides stable carrier reference while the PN sequence provides robust frequency and phase offset estimation through its autocorrelation properties, achieving reliable synchronization with reduced overall reference signal power
Data Source
AI summary
A method for demodulating a carrier wave in a channel environment in which a pilot signal may be distorted, in a digital TV receiver, which may receive a vestigial sideband (VSB) modulated and transmitted signal, and a demodulation apparatus therefor are provided. A field synchronization part of a VSB signal, in which a pilot signal may be removed, may be used as a reference signal for synchronization. The frequency offset of a carrier wave may be estimated through self-correlation of a signal, and the phase offset of the carrier wave may be estimated through a pilot-less frequency and phase locked loop (FPLL).