Time Synchronization in ATSC 3.0 Digital TV Systems
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Solution Overview
Problem
The existing ATSC 8-VSB modulation system is vulnerable to multipath propagation and Doppler Effect, particularly in metropolitan areas and when delivering content to portable/handheld/vehicular devices, and requires an efficient time synchronization mechanism that can handle different frame creation modes in the upcoming ATSC 3.0 standard.
Innovation Solution
Incorporating a time synchronization indication mechanism that includes a modulator generating signals with time offset and frame length parameters, transmitted over a communication medium, and a receiver that demodulates these signals to maintain synchronization, accommodating both time-aligned and symbol-aligned frame modes without reducing transmission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If 8-VSB modulation system is used, then current ATSC standard compatibility is maintained, but vulnerability to multipath propagation and Doppler Effect increases
Solution Approach 1:
The patent changes the modulation parameter from single-carrier 8-VSB to multi-carrier OFDM modulation. This parameter change fundamentally improves robustness against multipath propagation and Doppler Effect by distributing information across multiple orthogonal subcarriers, where only a subset of subcarriers are affected by fading at any given time, enabling reliable reception in mobile and metropolitan environments.
2Reliability
If time synchronization information is transmitted periodically in data stream, then time locking between transmitter and receiver is achieved, but transmission efficiency decreases
Solution Approach 1:
The patent merges time synchronization information with existing frame structure elements (preamble, bootstrap, or data segments) rather than transmitting separate periodic synchronization signals. The time offset and frame length parameters are embedded within the existing data stream structure, allowing synchronization to be achieved without adding separate transmission overhead, thus maintaining transmission efficiency while ensuring accurate time locking.
Solution Approach 2:
The system uses the existing frame structure elements (which are already being transmitted for other purposes) to carry time synchronization information. The preamble, bootstrap, or data segments that are necessarily transmitted for frame delimitation and data delivery also convey time offset and frame length parameters, making the synchronization mechanism self-sufficient without requiring additional dedicated resources.
3Adaptability or versatility
If two modes of frame creation are allowed, then system flexibility increases, but time recovery mechanism complexity increases
Solution Approach 1:
The patent implements a universal time synchronization mechanism that works across both frame creation modes (time-aligned and symbol-aligned). The same basic approach of embedding time offset and frame length parameters within existing frame structure elements is used for both modes, with the parameters themselves indicating which mode is being employed. This universal approach avoids the need for completely separate time recovery mechanisms for each mode, reducing overall system complexity while maintaining flexibility.
Data Source
AI summary
Methods (900, 1000) and apparatuses (110, 120, 400) are provided for transmitting and receiving a signal. The method (900) of transmitting a signal includes modulating (920) data into a plurality of modulation symbols to generate a signal, the data including time synchronization information including one of a time offset parameter and a frame length parameter selected according to a frame length mode parameter, and transmitting (930) the signal over a communication medium. The method (1000) of receiving a signal includes receiving (1010) a signal over a communication medium, and demodulating (1020) the signal to generate a plurality of demodulated symbols, the demodulated symbols including data, the data including time synchronization information including one of a time offset parameter and a frame length parameter selected according to a frame length mode parameter.