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Will the Stars Align for 5G Ultra Low-latency Services?

March 23, 2021
By Jon Baldry
Director, Metro Networking

The changing role of GPS and GNSS in 5G network synchronization

5G network deployments are well underway across the globe, with many network operators now preparing for the more advanced “Phase 2” 5G services such as ultra-reliable low-latency communications (uRLLC) services. Key to enabling these advanced services is advanced radio access network (RAN) capabilities that push advanced features and performance requirements, such as significantly improved synchronization delivery to the cell tower, on to the underlying transport network.

At Infinera we’ve seen a distinct shift over recent months in network operators’ focus on synchronization distribution strategies and underlying network synchronization performance. In the first in a series of blogs covering this important topic, we’ll look at how the migration to 5G is changing network operators’ usage of global navigation satellite system (GNSS) within these networks.

The delivery of synchronization information in mobile networks is achievable through several different mechanisms and strategies. The uptake of these various options has varied across the geographic regions of the globe due to technical and geopolitical reasons. The main synchronization delivery options are:

  • Synchronization/timing signals from a GNSS, such as the U.S.’s Global Positioning System (GPS), Europe’s Galileo, Russia’s Global’naya Navigatsionnaya Sputnikovaya Sistema (GLONASS), or China’s BeiDou Navigation Satellite System, directly to every location requiring synchronization in the network
  • Synchronization/timing signals delivered from key centralized GNSS-enabled locations in the network through the backhaul/transport network to all other locations requiring synchronization
  • Synchronization/timing signals delivered through a totally separate synchronization delivery network

Each approach has its own strengths and weaknesses, and operators across the globe have built synchronization strategies to best suit their own environments. For example, historically GNSS using GPS to every location has been the primary mechanism in North America, whereas Europe predominantly uses synchronization through the backhaul network with GNSS limited to key timing locations.

However, in recent years there has been an increase in the incidence of both deliberate and inadvertent hacking and jamming of GNSS as the use of cheap illegal GNSS jammers has increased and as some countries have even tested GNSS jamming and/or spoofing as part of military strategies. Due to the importance of network synchronization, these factors are leading some countries to introduce legislation to force protection and reliability into synchronization networks. It is possible to protect GNSS receivers from some of this jamming, but this greatly increases the cost per node.

Another consideration that mobile network operators must take into account as they move to 5G is the proliferation of cell sites, especially those in locations that are tough to reach from a GNSS perspective. 5G in dense urban environments will require millimeter-wave small cells that provide high-bandwidth connectivity over a shorter range, and operators are planning deployments of these in tough-to-reach locations such as deep inside shopping malls, cells per floor in high-rise office buildings, etc.

It should be stressed that while GNSS networks do occasionally suffer from interference and downtime caused by natural effects or deliberate jamming/spoofing, they are still highly reliable and form a key component of most synchronization networks. There are solutions to protect GNSS and deliver GNSS signals into tough locations, but overall, these factors are causing more and more operators that were previously GNSS-focused to plan to utilize network-based synchronization as a backup to GNSS at every node. In some cases, these operators plan to migrate fully to network-based synchronization, with GNSS limited to key centralized locations in the network that use these protection and resiliency methods to harden GNSS against attacks.

Network-based synchronization can take the form of either synchronization delivery through the transport network or through a totally separate dedicated synchronization delivery network. Both approaches provide the operator with the right level of synchronization performance, and backhaul network-based synchronization offers the opportunity for significantly better overall network economics as it avoids a complete overlay network for synchronization. Wherever possible, mobile network operators typically utilize backhaul-based synchronization delivery, but it should be noted that this is not always possible, and therefore, synchronization overlay networks cannot be discounted from the discussion.

Overall, there will always be a mix of strategies deployed across the globe, but the trend is moving more and more toward network-based synchronization delivery, and due to better economics, transporting this over the backhaul network is nearly always the primary option. Those network operators that have always deployed synchronization distribution through the transport network, and those now migrating to this strategy, need to now consider how their optical transport network can best support these challenging requirements economically.

For those readers that want to dive into this topic in more detail, our new Synchronization Distribution in 5G Transport Networks e-book provides a detailed overview of synchronization distribution challenges and standardization along with an end-to-end synchronization distribution strategy that meets the demanding requirements that 5G is driving into optical networks. I’m also presenting at this year’s Workshop on Synchronization and Timing Systems (WSTS) virtual event on March 30. I’ll be outlining how we can provide 5G-quality synchronization with optical timing channel-enabled in real-world networks. I hope those interested in 5G synchronization distribution can join me at this event. You can register here.