Single-Frequency Network Synchronization via Temporal Averaging
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Solution Overview
Problem
In simulcast networks, time synchronization between a control center and transmitters is challenging due to low frequency accuracy of the data rate in the short time horizon, leading to variable data rates and reduced time accuracy, which affects the transmission of data packets.
Innovation Solution
The method involves using a second reference time signal with low time and frequency accuracy in the short term and high accuracy in the long term, where temporal averaging of the time and frequency accuracy is applied to determine accurate transmission times for data packets, ensuring synchronized transmission despite variable data rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a second reference time signal with low frequency accuracy is used to generate the data rate, then cost is reduced, but time accuracy in the short time horizon deteriorates
Solution Approach 1:
The system dynamically switches between two reference time signals based on time horizon requirements. For short-term precision, it uses the first reference time signal with high frequency accuracy. For long-term stability, it uses the second reference time signal with low cost. This dynamic selection resolves the contradiction by allowing cost reduction while maintaining time accuracy when needed.
Solution Approach 2:
The system performs preliminary averaging of the second reference time signal's frequency characteristics before using it to generate the data rate. This preprocessing step improves the effective time accuracy of the low-cost reference signal, reducing its inherent inaccuracies and enabling cost reduction without severe degradation of time synchronization performance.
2Measurement precision
If temporal averaging of the second reference time signal is applied, then time accuracy is improved, but computational complexity increases
Solution Approach 1:
The system changes the time averaging parameter adaptively based on the observed frequency stability of the second reference time signal. When the reference signal shows good short-term stability, a shorter averaging window is used, reducing computational complexity. When stability deteriorates, the averaging window is extended to improve time accuracy. This adaptive parameter adjustment resolves the contradiction between accuracy and complexity.
3Adaptability or versatility
If the data rate varies in the short time horizon, then adaptation to the second reference time signal is achieved, but synchronization precision deteriorates
Solution Approach 1:
The system segments the data transmission into two distinct modes: short-term transmission using the first reference time signal for high precision synchronization, and long-term transmission using the second reference time signal for adaptability. By separating these functions temporally and functionally, the system achieves both adaptation and synchronization precision without mutual interference.
Solution Approach 2:
The system introduces an intermediary averaging mechanism that mediates between the variable data rate requirement and the precision requirement. This intermediary process smooths out the variations in the second reference time signal before applying it to data rate generation, reducing its impact on synchronization precision while maintaining adaptability.
Data Source
Figure 1~2
Figure 3~4B
Figure 5A~5B
AI summary
The invention relates to a method and a system for the synchronisation of a central station (1) and several transmitters (21, 22,..., 2i) in a single-frequency network. According to said method, a first reference time signal ( SREF1) is generated with a high degree of time and frequency accuracy on the short and long time horizon and a second reference time signal (SREF2) is generated and supplied to the central station (1) with a low degree of time and frequency accuracy on the short time horizon and a high degree of accuracy on the long time horizon. The system then generates a transport data stream (Sten) with a temporally variable data rate ( fVAR ) that corresponds to the frequency of the second reference time signal (SREF2) by means of the central station (1), said stream (Sten) being supplied to several transmitters (21, 22,..., 2i) and comprising distributed data packets (n(i)) that contain the transmission instant (tsende1, tsende2,...., tsendei) of the data packet (n(i)), referenced to the second reference time signal (SREF2), for the transmitters (21, 22,..., 2i). The time accuracyof the transmission instant (tsende1, tsende2,...., tsendei) of each data packet (n(i)) is thus optimised by averaging the time and frequency accuracy of the second reference signal over time (SREF2). The system temporally offsets the transport data stream (Sten) received by each transmitter (21, 22,...,2i) from the central station (1) until the data packets of the transport data stream (Sten) that each contain a transmission instant (tsende1, tsende2,...., tsendei) are transmitted at the correct transmission instant (tsende1, tsende2,...., tsendei) with regard to the first reference time signal ( SREF1) supplied to each transmitter (21, 22,...,2i).