Distributing high-precision time over optical networks in the 5G world

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By Eric Colard
Head of Emerging Products, Frequency & Time Systems
Microchip Technology

Mobile operators are investing heavily in the deployment of LTE-Advanced and 5G networks that will transform cellular communications and connectivity.

They face big risks, though: the high-performance mobile services delivered over these networks are extremely dependent on precise time from GPS and other similar regional constellations broadly known as GNSS so they can synchronize radios, enable new applications and minimize interference.

If GPS/GNSS becomes unavailable due to jamming, spoofing, failures or other events, the resulting service disruption would have a catastrophic impact on system performance.

Just like the energy grid is extremely vulnerable to climate, heat, winds and dry vegetation that can lead to fires on a large scale as seen in California recently, 5G networks are vulnerable to disruptions in the distribution of precise time that can lead to total systems outage.

New technologies enable mobile operators to protect their networks from these threats. These technologies make use of existing deployments while creating new architectures for distributing very high-precision time over long distances. They minimize additional costs while offering the necessary performance to meet the demanding requirements of 5G.

Technology landscape

The latest LTE-Advanced and 5G mobile networks bring tremendous capacity and bandwidth gains that are being used to deliver new services to consumers, industries, cities and specific market segments. From high-bandwidth video delivery for smartphones to autonomous vehicles, smart cities and the internet of things (IoT) for smart factories, these new services all rely on the synchronization of numerous sensors, base stations and other devices.

Accomplishing this requires the delivery of very precise time over long distances. Without it, mobile operators cannot maximize deployment investments by minimizing disruptions and risk.

They also must devise plans they can leverage in case of GPS/GNSS malfunction. At the same time, they need to take advantage of optical networks and other existing infrastructure so that they don’t require expensive new investment in dark fiber.

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Meeting stringent requirements

Standards bodies have defined stringent requirements for precise time and synchronization such as Prime Reference Time Clock (PRTC), which includes 100-nanosecond (ns) PRTC Class A (PRTC-A), 40-ns PRTC Class B (PRTC-B) and 30-ns enhanced PRTC (ePRTC) performance specifications.

To meet these requirements, a high-quality source of time is an absolute must and a very resilient, efficient and performant distribution mechanism is required to transport time from the source to the various devices consuming time (for example, base stations, sensors and vehicles).

The problem with relying on GPS/GNSS for meeting these requirements is that its deployment can be expensive given the increasing densification of endpoints. There is also a technical vulnerability associated with GNSS receivers located at cell sites.

If the GNSS receiver cannot track satellites properly for whatever reason, the radio must be removed from service quickly to avoid interference issues due to the short holdover period of the oscillator technologies used in the radios. Because of these technical and financial considerations, operators are very motivated to find solutions where GNSS dependency is reduced or even eliminated at many locations.

Another set of considerations for operators includes:

• the distribution of time from the source to the endpoints using the network;
• the network nodes; and
• the various synchronization capabilities these network nodes can support.

Typically, a precision time protocol (PTP) grandmaster is located at the beginning of the timing chain and complies with 100ns PRTC-A or 40-ns PRTC-B so it can deliver precise time to the end of the chain within +/-1.5 microseconds. The network nodes on the path typically embed a Time Boundary Clock (T-BC) capability that meets either Class A (50-ns) or Class B (25-ns).

A new type of time-distribution architecture is needed to address these requirements and considerations so operators can protect their mobile network against GNSS disruption and distribute precise time over long distances for national coverage. This architecture must also deliver the necessary performance to meet end-to-end budgets for 5G needs.

A different time-distribution architecture

There are multiple capabilities a high-precision time-distribution architecture should feature so that operators can most effectively mitigate GPS/GNSS vulnerabilities and solve other challenges in their 5G networks. The architecture should:

• leverage the existing optical network (thus avoiding high cost dark fiber expenses)
• use a dedicated lambda in order to transport time in the most rapid manner
• protect, to the utmost level, a redundant source of time that meets the highest, 30ns ePRTC performance and uses a combination of Cesium and GNSS as the source of time
• have two directions for the flow of time (East and West) so that a redundant path can be leveraged in case of any issues along the way from source to endpoint
• have a chain of high-precision boundary clocks (HP BCs) that can meet the highest level of performance defined by today’s standards (T-BC Class D 5ns)

A multi-domain architecture of this type offers the redundant, sub-microsecond end-to-end timing capabilities that are required to affordably deliver the high performance, 5-nanosecond per node distribution of precise time over hundreds of miles.

An example of this type of solution is Microchip’s TimeProvider 4100, which can be configured as either an ePRTC at the source of the timing chain with PRTC-A and PRTC-B time-delivery capabilities to various end nodes, or an HP BC on the optical network path.

This type of product can also be configured for application-specific requirements, end to end, with up to nanosecond precision time-delivery capabilities over long distance.

Assuring precise timing

The success of a coming generation of high-performance mobile services will depend on how well operators address today’s critical GPS/GNSS vulnerabilities. Jamming, spoofing, failures or other events can disrupt the precise GPS/GNSS timing that 5G networks need for synchronizing radios, enabling applications and minimizing interference.

The latest high-precision time-distribution architectures mitigate these risks with minimal additional cost and give operators the performance they need to support demanding new 5G services ranging from IoT-based applications to receiving high-bandwidth video on smartphones.

Microchip has released version 2.1 for its TimeProvider 4100 timing grandmaster.

Eric Colard leads product line management for Microchip’s TimeProvider 4100 and Integrated GNSS Master solutions for the telecom, utility and other industries. Colard’s leadership includes product definition, customer interaction, outbound promotions and business development.

He has held successive technical and leadership roles at technology companies in the U.S. and Europe. He began his career as an engineer in the networking arena on X.25, frame relay and other protocols at companies including Alcatel and Cap Sesa Telecom. He later held successive product management and business development leadership roles in networking, security, and other areas at Novell, Tumbleweed, FaceTime and Vernier Networks.

As the industry rapidly progressed, Colard increasingly became involved in wireless data compression and TCP/IP optimization. In 2007 he joined Symmetricom and architected and built the SyncWorld ecosystem with partners Alcatel-Lucent, Ericsson, Nokia Siemens and Cisco. Through acquisition Symmetricom became part of Microsemi, which today is part of Microchip.

Colard holds bachelor of science and master of science degrees in computer science, both from Ecole Nationale Superieure des Telecommunications (now Telecom ParisTech) in Paris, France. He is a member of the Metro Ethernet Forum (MEF), Open Compute, Telecom Infra Project and Small Cell Forum. He has received an award for his industry contributions from the Small Cell Forum.