将5G网络与TCXOS同步| Electronic Design - beplay体育app官方下载

What you’ll learn:

为什么在网络同步中稳定时钟对于使5G成为现实至关重要。
Why TCXOs are needed.

5G mobile technology is poised to profoundly change the way the world communicates, dramatically improving everything from massive Internet of Things (IoT) networks, AI, and virtual reality, to security, robotics, and cloud computing, to name just a few applications.

These 5G networks will connect machines and devices at higher data speeds than their 4G network predecessors and combine that with ultra-low latency. But to maintain consistent operation and high reliability, network components must be synchronized.

准确的时间(时钟)plays a crucial role in maintaining synchronization within a mobile network. Inaccurate synchronization and timing can lead to interference between nodes in a radio access network (RAN), which is the part of a wireless system that connects individual devices such as smartphones and smart devices to other parts of a network through a radio link. Error-prone oscillators and clocks can cause time shifts that degrade network performance and reliability.

That’s why stable clocking in network synchronization is critical to making the transformative potential of 5G a reality. Temperature-compensated crystal oscillators (TCXOs), which are designed to operate in high-temperature environments, hold the key.

Oscillators are electronic circuits that use a crystal to generate a periodic electrical signal with constant frequency, also known as a clock or timing signal. Most digital circuits rely on clock signals to synchronize the different components within them.

Clocking and Synchronization in 5G Applications

A RAN优化了5G应用程序的服务性能和可靠性。它由不同的同步组件组成，每个组件都贡献了共同提供所需服务的独特功能。定时准确性和可用性以及成本是最终产品的重要考虑因素。

An open RAN architecture typically consists of a remote radio unit (RRU), fronthaul switch, and a distributed unit (DU), with a TCXO or OCXO (oven-controlled crystal oscillator) generating the clock signal to synchronize these devices. These components need to be precisely synchronized to avoid data packet loss and system interruptions.

许多5G网络依赖于时间划分双工（TDD），这是一种双工通信方法，其中基于同一频段的时间分配将入站信号与出站信号分开。TDD要求所有设备都必须精确同步。

The synchronization frequency is typically based on the IEEE 1588 Precision Timing Protocol (PTP), though Synchronous Ethernet (SyncE) is another standard that’s occasionally used. The network architecture dictates whether PTP, SyncE, or both are employed for synchronization.

In PTP, a棋圣设备使用同步源（通常基于GPS）来创建几个时间戳PTP数据包，这些PTP数据包已交付给其他位置的追随者时钟。数据包计算了大师和追随者时钟之间的时间偏移，之后，随着追随者时钟在其位置生成本地时钟信号。PTP是一个智能系统，可以适应大师的损失。

Synce是一个较旧的系统，其中使用高质量的时钟参考（通常来自GPS或剖腹时钟源）来计算网络核心的输出。在网络上的其他位置进行时钟恢复，分析输出信号的信号边缘，并利用它们为接收设备得出自己的时钟信号。

The DU must pass a precisely synchronized timing signal to the fronthaul switch and a RRU. DU clocking must be heat resistant under a heavy load; otherwise, it will require adding a fan to the system. And the RRU must be environmentally robust since it’s usually placed outdoors on rooftops and poles, and near roads and highways.

Oscillator Challenges in 5G Applications

Environmental stress can influence oscillator performance. 5G networks rely on a large density of radios, which are often mounted in locations vulnerable to vibration from sources, such as trucks, trains, cars, wind, and thunder. These devices also experience significant swings in temperature. Consequently, oscillators deployed in these radios must maintain stable performance during environmental stress to prevent dropped links.

Cost and availability—as well as size, heat, and power—are important considerations for engineers, too. TCXO and microelectromechanical-system-based (MEMS) oscillators are replacing other types due to their performance and affordability.

However, low-cost MEMS oscillators can introduce additional constraints. They may not react well to physical-layer rearrangement, and typically don’t support the necessary bandwidth for PTP G.8275.2, limiting them to the lower bandwidth used in the G.8275.1 PTP profile.