Net Insight’s GPS-independent and inexpensive technology for synchronization transmitters in TV networks is a perfect fit for 5G

Swedish technology makes 5G networks keep time

Synchronization of 5G base stations needs to be kept below one microsecond or the network will stop working. Swedish company Net Insight has a robust and affordable solution for clock distribution over existing infrastructure in nationwide mobile networks. Türk Telekom is the first customer.

Just before Christmas a large delegation from the Turkish operator—including the CEO and CTO—visited Stockholm to sign an agreement with Net Insight, making the company a partner and supplier of time synchronization for Türk Telekom’s mobile network in Turkey.

“We built a VAR system [decision review for soccer referees] for Türk Telekom which they tested as early as 2017, and which was implemented in 2018. They had heard about our solution for time synchronization and contacted us to ask if we could help them with the 5G roll out,” Per Lindgren, CTO and co-founder of Net Insight explains.

The agreement is worth SEK 220 million and runs until 2026. SEK 55 million will be used on product development.

“There is already a product and we are now working to improve accuracy, redundancy and manageability.”

The demands on synchronization are far higher across all parts of a 5G network compared to LTE, by a factor of 20 to 50. The reason is that large volumes of 5G traffic is time division duplexed (TDD) and needs to work for real time services such as remote control vehicles or factories. Latency in radio traffic cannot be more than a microsecond.

In practice, this means that accuracy in mobile network nodes must keep time within a couple of nanoseconds. This also needs to be done using an external reference so that overlapping mobile networks from different operators do not disrupt each other.

“We developed the solution as early as 2006 for the digital TV network and built the first large network for Norkring in Norway.”

Demands on the Norwegian TV network included that it needed to be GPS-independent, following a number of incidents when it was disrupted during NATO exercises.

Using the clocks in satellite positioning systems such as GPS or Galileo as a time reference is inexpensive and provides accuracy of a few tenths of a nanosecond. However, the signals are weak and easy to disrupt.

“The first tests were carried out in Turkey in 2019 during the Syrian war. For most of the time there was no GPS signal in Ankara, which highlighted the need very clearly,” Per Lindgren explains.

GPS is also subject to problems with spoofing, which involves false GPS signals that are stronger than the real signal and provide recipients with the wrong position and time. In Galileo this has been fixed using encryption.

“This means that many countries require 5G networks to be satellite independent to be awarded a license, and PTS in Sweden requires all mobile networks to be independent of foreign systems, including satellites by 2025.”

Protocol IEEE1588, also known as PTP, constitutes a standard protocol for clock distribution with sufficient accuracy for use in mobile networks. However, this requires hardware support in every node.

“This works well if you are constructing an entirely new network, and in urban areas. But it gets expensive when you want to upgrade and replace an entire national network. The main difference is that we can use existing IP networks – we build an overlay network and have managed over 24 router hops where 1,200 km was the longest,” Per Lindgren continues.

Net Insight’s solution resembles IEEE1588 but can compensate for the asymmetries and congestion that always exist in IP networks.

Tests show that synchronization accuracy is a couple of hundred nanoseconds, and the solution works regardless of whether Huawei, Cisco, Ericsson or someone else has delivered the underlying infrastructure.

“It is also fully interoperable with PTP, so if you have PTP in one part you can use that, and use our solution to reach the areas that don’t.”

Like NTP (Network Time Protocol), PTP (Precision Time Protocol) is a protocol for clock distribution in networks.

“Fundamentally we use the same technology as for time stamps. We send and receive time-stamped messages.

The message is then sent back using the same procedure, and latency can be calculated when it returns to the starting point.”

“There are two problems, achieving exact time stamps if there is a lot of jitter (latency variation), but the main problem relates to asymmetries, i.e. different latencies in the uplink and downlink.”

To just divide the time it takes for the signal to get there and back by two generates a phase error.

“Here, we have unique capability in handling this by using profiles,” Per Lindgren explains.

The company’s solution capitalizes on the fact that the signal can take several alternative routes to reach the recipient, which is used to create a profile.

“This means that we can discover asymmetries and compensate for them. Our algorithms generate tenfold higher accuracy than PTP.”

The potential for redundancy is another advantage. If a node malfunctions, the signal can take a different route to reach its intended destination.

“This solution exists in PTP but the process is relatively manual. Our thinking is network before synchronization, so we always find the best route and can also use several different routes. These are not present in PTP.”

Depending on the construction of mobile networks, new hardware may be required in the nodes even if the algorithm itself does not need more computational power than needed to operate using existing network hardware.

If the operator uses a modern radio network (RAN) that is fully PTP-compatible, it is enough to just add the software.

“It then works as standard PTP, the system does not pick up whether it is us or another boundary clock.”

However, many operators lease transport capacity in fiber networks. To manage this, extra hardware is needed.

“In Turkey, we will construct the network using hardware in the base stations. They want to be entirely independent,” Per Lindgren explains.

With regard to the reference clock, operators usually decide where it should be sourced. In Sweden everyone uses Netnod, but it is possible to use several different reference clocks which further increases reliability.

Regardless of which clock you use it should be synchronized with UTC, Coordinated Universal Time, which is the global time standard. This ensures that all networks use the same time reference and can coexist.

Normally, Net Insight receives time in the form of a PTP signal and transmits it in the same way to the nodes. This takes place a few thousand times per second so the clocks in the individual nodes do not need to be particularly accurate.

“Because we offer improved accuracy closer to the network edge than for traditional solutions, we offer a better timing budget as there is more margin in the final hops.”

The largest network in operation today is the Norwegian digital TV network with approximately 800 nodes. A mobile network can have over 10,000 nodes, which places much higher demands on easy management, upgrading and error trapping in the nodes.

But the hardware also needs to be developed. A great deal has happened since the first version was launched, and it can now be built much more inexpensively.

“The market is exciting and there is a window of opportunity right now. The solution can also be used in other time-critical networks such as power grids and emergency services.”

This article was first published in Swedish in Elektroniktidningen (cover and pages 14-15).