700 MHz Frequency Migration Project: Single Frequency Network Verification and Failure Case Analysis

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This paper focuses on the verification of the ground digital television single frequency network under the background of the 700 MHz frequency migration and the analysis of failure cases caused by resource scarcity. The research team analyzes actual cases to reveal potential issues encountered in the construction of the single frequency network, such as incompatibility of transmission equipment for transparent transmission, conflicts caused by local program insertion, and misalignment of exciter delays, and proposes solutions. The paper details the steps for troubleshooting and optimization measures, emphasizing the importance of transparent transmission, the standardization of local program management, and the consistency of exciter delays as key factors for ensuring the stable operation of the single frequency network. Furthermore, the workflow summarized for eliminating interference provides practical guidance for related operation and maintenance work, helping to improve the operational efficiency and service quality of the ground digital television system, serving as an important reference for industry practice and theoretical research.

Authors:

Gao Yang, Yang Fan, Wang Yi, Shen Bohao

National Radio and Television Administration, Broadcasting and Television Planning Institute

First Author Profile:

Gao Yang, Senior Engineer, born in February 1988, graduated from Communication Engineering at Communication University of China in 2011, working in the Wireless Research Institute of the Broadcasting and Television Planning Institute of the National Radio and Television Administration, mainly engaged in research on testing methods related to the broadcasting and television industry. In recent years, he has mainly participated in the technical scheme formulation and related testing of the 700 MHz frequency migration project, research on 5G and satellite broadcasting and television interference, all-digital planning, emergency broadcasting, and smart operation and maintenance.

NO.0

Introduction

After the completion of the national ground digital television 700 MHz frequency migration, the available frequency resources for ground digital television have decreased by one-third, and the single frequency network will become the main coverage network form in the future. After construction, ensuring successful networking, achieving expected coverage effects, guaranteeing stable operation, and resolving user complaints caused by network failures have become key concerns for operation and maintenance agencies. This article analyzes actual cases from the acceptance testing of the single frequency network in the 700 MHz frequency migration project, identifies potential issues in single frequency network construction, provides troubleshooting methods, and summarizes the workflow for eliminating interference, offering ideas and solutions for the establishment, operation, and maintenance of the single frequency network.

NO.1

Single Frequency Network Implementation Form

The ground digital television broadcasting single frequency network involved in this 700 MHz frequency migration project is based on the baseband code stream allocation form. The single frequency network TS stream signal distribution network mainly uses satellite and IP-based transmission systems. In the satellite transmission system, the single frequency network adapter is located at the satellite uplink station, and the station receives and demodulates the satellite signal before synchronizing the broadcast; in the IP transmission system, the adapter is located at the provincial signal transmission master station, and each province needs to configure parameters independently to ensure successful networking.

NO.2

Single Frequency Network Synchronization Verification

2 Single Frequency Network Synchronization Verification

2.1 Overlapping Coverage Area of Single Frequency Network

The overlapping coverage area of the single frequency network refers to the area where two or more useful transmitting signals simultaneously cover within the coverage of the ground digital television broadcasting single frequency network, and the difference between the main signals from different sites is less than the RF protection ratio value. This area is the key area for conducting single frequency network verification tests, as shown in the channel impulse response graph tested in the overlapping coverage area below.

700 MHz Frequency Migration Project: Single Frequency Network Verification and Failure Case Analysis

Channel Impulse Response in Overlapping Coverage Area

2.2 Testing Method

The single frequency network synchronization verification test is mainly conducted using outdoor fixed reception, and coverage simulation results are used to determine the range of overlapping coverage areas. Open locations are chosen to reduce multipath effects, using a 4-meter antenna and receiver to monitor reception status and signal response.

During the test, the station transmitter is turned on individually, and the antenna is adjusted to the direction of the signal, observing the reception status. After determining the test point, the station remains powered on, and the antenna is rotated to observe the reception status. If the signal is received normally and displays signal delay and strength, it indicates synchronization status.

By directing the antenna and observing the strength displayed by the receiver, the order and delay of signal arrival can be judged. The theoretical delay value is calculated in conjunction with delay settings and actual distance, comparing it with the test value to judge the credibility of the result. The field strength, signal-to-noise ratio, and location information are recorded to complete the test.

The following actual case is used as an example to compare test values and theoretical values. It is known that the delay settings of stations A and B are provided; the test data shows that the signal amplitude of station B is higher, and the signal from station A arrives earlier and is closer. The map shows that station A is 12 kilometers closer than B, with a delay difference of -6μs. The distance displayed by the receiver is basically consistent with the map distance and delay difference, proving the result’s credibility. When calculating, the order of stations must be unified and the sign recorded.

700 MHz Frequency Migration Project: Single Frequency Network Verification and Failure Case Analysis

Distance and Orientation Relationship between Test Point and Measured Station

2.3 Precautions

This 700 MHz frequency migration project involves the co-frequency protection ratio requirements for Central 8 and Central 4 programs, as shown in Table 1.

700 MHz Frequency Migration Project: Single Frequency Network Verification and Failure Case Analysis

Table 1 Co-frequency Protection Ratio Requirements

In a non-synchronized state, by adjusting the antenna direction, the signal strength difference is made greater than the protection ratio. Professional testing receivers can receive and display the relative delay and strength of signals, but at this time, it cannot be determined whether the single frequency network has been successfully established.

NO.3

Network Failure Case Analysis

3.1 Incorrect Configuration of Single Frequency Network Adapter

A certain province adopted a “fiber + IP” network to achieve single frequency network coverage across the province. During the 700 MHz frequency migration test, it was found that a certain city experienced network failure, with no response when adjusting the transmitter delay; central program transmission was normal. After checking the equipment and finding no issues, it was speculated that there was a problem with the configuration of the total front-end single frequency network adapter. Upon inspection, it was found that the Maxdelay setting value of this program’s single frequency network adapter was less than the transmission link delay of the city site, resulting in network failure. After resetting the Maxdelay value, the network resumed normal operation.

3.2 Transmission Equipment Does Not Support Transparent Transmission or Local Program Insertion

During a certain city’s single frequency network test, network failure was discovered, finding that station A’s insertion of local programs into the central program caused the failure, as shown in the figure below.

700 MHz Frequency Migration Project: Single Frequency Network Verification and Failure Case Analysis

Central Program Inserting Local Program

After communication, the station removed the local program, but the network still failed. Inspection revealed that the station had not bypassed the multiplexer nor set up transparent transmission. After removing the multiplexer, the station participated in the network normally.

It is recommended that the transmitting station streamline the program transmission link, eliminate unnecessary equipment, reduce failure points, and ensure stable program transmission in the single frequency network.

3.3 Exciter Basic Delay Not Aligned

The exciters purchased for this 700 MHz frequency migration project had completed compatibility testing and basic delay alignment before leaving the factory. However, in actual use, it was found that there were basic delay differences between different batches of the same manufacturer and between newly purchased and reused exciters, leading to single frequency network failure. To ensure smooth networking, we will conduct basic delay calibration of the exciters at the station, ensuring all exciter delays are consistent.

The testing process is as follows: connect a standard exciter to the measured network, adjust its working mode, frequency, and power to be consistent with the measured exciter; combine output, connect the test instrument; observe the demodulation situation; if normal, check the delay difference, which should be less than 1μs to meet requirements; otherwise, adjust the delay to be less than 1μs. If demodulation cannot be performed normally, it indicates that the measured exciter delay exceeds the allowable range and needs recalibration at the factory.

NO.4

Network Fault Troubleshooting Process

Practice has proven that for ground digital television single frequency networks based on baseband TS code stream distribution, as long as the relevant code stream transmission equipment meets 100% transparent transmission, and the recovered TS code stream SIP jitter value meets the requirements, the single frequency network can be successfully established.

When a single frequency network failure is detected, first check the settings of the total front-end single frequency network adapter, including system payload rate and Maxdelay value; secondly, check whether the equipment in the transmission link supports and is set to transparent transmission mode; then check whether the station has inserted local programs; next, check the jitter and delay of the TS code stream received by the transmitter’s exciter; finally, check whether the reference delay of the single frequency network exciters used at each station is aligned.

NO.5

Conclusion

This article introduces the testing methods for verifying the networking of ground digital television single frequency networks, summarizes the cases of single frequency network failures in the 700 MHz frequency migration project, and provides solutions and workflows. This work can serve as a reference for establishing ground digital television single frequency networks across the country in the future, improving wireless transmission levels and quality, and assisting in the safe broadcasting of radio and television.

end

700 MHz Frequency Migration Project: Single Frequency Network Verification and Failure Case Analysis

References

[1] GD/J 066-2015. Technical Requirements and Measurement Methods for Ground Digital Television Single Frequency Network Adapters Based on Satellite Transmission[S].

[2] GD/J067-2015. Technical Requirements and Measurement Methods for Ground Digital Television Single Frequency Network Exciters Based on Satellite Transmission[S].

[3] National Quality Supervision, Inspection and Quarantine Administration, National Standardization Management Committee of China. Technical Requirements for Ground Digital Television Broadcasting Single Frequency Networks: GB/T 28433—2012[S]. Beijing: China Standard Press, 2012.

[4] National Quality Supervision, Inspection and Quarantine Administration, National Standardization Management Committee of China. Technical Requirements and Measurement Methods for Ground Digital Television Broadcasting Single Frequency Network Adapters: GB/T 28434—2012[S]. Beijing: China Standard Press, 2012.

[5] National Quality Supervision, Inspection and Quarantine Administration, National Standardization Management Committee of China. Technical Requirements and Measurement Methods for Single Frequency Network Time Reception Equipment: GB/T 34995—2017[S]. Beijing: China Standard Press, 2017.

[6] National Quality Supervision, Inspection and Quarantine Administration, National Standardization Management Committee of China. Frame Structure, Channel Coding, and Modulation for Digital Television Ground Broadcasting Transmission Systems: GB 20600—2006[S]. Beijing: China Standard Press, 2007.

[7] National Quality Supervision, Inspection and Quarantine Administration, National Standardization Management Committee of China. Objective Assessment and Measurement Methods for Ground Digital Television Broadcasting Signal Coverage Quality Part 1: Outdoor Fixed Reception: GB/T 28438.1 -2012 [S]. Beijing: China Standard Press, 2012.

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