Clock synchronization device in single-frequency network

Abstract

The invention provides a clock synchronization device in a single-frequency network, which comprises a code stream recovery unit, a local crystal oscillation unit, a phase locked loop unit and a digital signal processor. In the invention, a code stream clock is recovered by using a universal chip through a TS (Transmission Stream) which is uniformly transmitted in the single-frequency network, and a local crystal oscillator is locked on the recovered code stream clock by using a phase locked loop chip. A reference clock output by the clock synchronization device has the advantages of high precision, simple structure and low cost; the dependence on an external GPS (Global Positioning System) synchronous reference clock is avoided; and the clock synchronization device can be completely used for replacing the traditional expensive GPS synchronous reference clock equipment to synchronize the clock and frequency in the whole single-frequency network.

Description

technical field [0001] The invention relates to a device in the technical field of digital signal processing, in particular to a clock synchronization device in a single frequency network. Background technique [0002] In the digital signal transmission system, in order to increase the coverage and improve the coverage effect, in a certain geographical area (city, province, or even a country), multiple transmission points are used to transmit the same wireless signal at the same time through a frequency band. Signal, so as to achieve reliable coverage of the geographical area, this networking method is called single frequency network. [0003] Single frequency network networking is the best way to expand coverage and improve coverage quality. Compared with multi-frequency network networking that consumes spectrum resources and has complex spectrum planning, it is especially important in today's rare spectrum resources. . The core technical issue of the single frequency net...

AI Technical Summary

Problems solved by technology

[0005] This method has four defects: each launch point needs a standard clock to ensure that the time between each launch point is fully synchronized, and the external GPS clock reference equipment that needs to be added is expensive and maintains high costs; the entire single-frequency The network relies on information outside the system to work, and the GPS system outside the single frequency network system is easily subject to human interference. Once the GPS is out of lock, the reference frequency of each transmission point will be lost, and the transmission frequency of each transmission point will be different. Lead to the collapse of the entire single frequency network; even the natural environment (such as lightning strikes, solar storms and other irresistible factors) can easily cause the GPS system to be interfered. Once the GPS is out of lock, the reference frequency of each transmission point is lost, and each transmission point The transmission frequency of the mobile phone will vary, which will lead to the collapse of the entire single frequency network; the recovery time of the GPS system after power-on and loss of lock is very long, measured in hours, resulting in the failure of the entire single frequency network to quickly enter the normal working state

Compared with the traditional method, this has indeed improved to a certain extent. However, this technology needs to insert counting operations at the main SFN adapter and the receiver adapter (synchronizer) at the transmitting end at the same time, so only specific dedicated equipment, or the original equipment must be technically transformed, which is not universal, especially not conducive to the interconnection and intercommunication of equipment from different manufacturers; secondly, it requires an additional time stamp inserted in the TS stream, which destroys the original TS stream The last and most important thing is that the clock recovery algorithm belongs to the tracking algorithm. Since the digital signal processor needs to calculate the value on average within a certain period of time, the tracking frequency is very low, which leads to the recovered clock is prone to jitter back and forth

To achieve high precision in engineering applications, the only way to greatly extend the locking time (up to several hours or even days), which is not conducive to engineering applications and my country's national conditions

For example, if the launch device needs to be turned on and off every day, if it takes several hours to lock the clock every time, the engineering practicability will be greatly reduced

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