As discussed in our previous blog, 5G user experiences that require ultra-fast speeds or ultra-low latency pose significant performance demands on the 5G radio and fronthaul networks. Fact is, enhanced radio techniques that are essential to assuring 5G’s user experience benefits all rely on a tightly synchronized 5G fronthaul network. But where to start?
Getting 5G fronthaul in sync
Operators have typically relied on GNSS/GPS for network time synchronization. However, to realize the full potential of 5G and take advantage of new spectrum, highly accurate time synchronization is needed. The requirements for Radio Access Network (RAN) timing and synchronization depend on the radio technology and the spectrum used. In addition, they depend on whether synchronization is taking place between neighboring radios or across the whole network.
The primary spectrum usage technique for 5G is expected to be TDD (Time Division Duplexing) to support high bandwidth 5G connections. Although currently deployed in several commercial 4G networks, the need (and performance requirements) for 5G will be greater.
TDD requires tight time and phase synchronization to protect against interference. For TDD, fronthaul network base stations must be synchronized to within 3µs of each other, or to within 1.5µs of a central time reference. This is still a fundamental requirement in 5G, but the synchronization requirement for some fronthaul applications can be far tighter.
Challenges in meeting 5G synchronization requirements
A range of enhanced radio techniques have been proposed, many of which involve the inter-operation of cells within a local area. This clustering further tightens the synchronization requirements between local Remote Radio Units (RRUs).
For example, 4G operators were able to aggregate two carrier frequencies to form a high-bandwidth pipe that would increase data rates to consumers, with the frequencies transmitted from the same antenna. With 5G, however, frequencies from multiple RRUs in a local cluster can be aggregated. To enable this, the RRUs must be synchronized to within 260ns of each other—a more than tenfold increase in accuracy from the base network requirement.
Delivering synchronization over Ethernet
Whether a whole network or cluster approach is taken, the synchronization requirements for 5G fronthaul are more rigid than we’ve ever seen before.
To meet these requirements, the ITU-T has defined a new series of recommendations, building on those already defined for the use of Synchronous Ethernet (SyncE) and Precision Time Protocol (PTP) to deliver synchronization over Ethernet, and intended to deliver an order of magnitude better performance than those defined for 3G and 4G.
New enhanced accuracy classes have been defined for boundary and slave clocks for applications such as fronthaul networks. The time error produced by the highest specification boundary clock (Class D T-BC) must be less than 5ns, and less than 30ns for Class C T-BC clocks.
5G provides a wide diversity of potential fronthaul network configurations, all of which require high accuracy. So how do manufacturers or operators ensure that requirements are being met?
Testing 5G fronthaul synchronization
The first step in test and validation is to test each device individually to ensure it meets the required specification. In the case of Class C T-BC and Class D T-BC clocks, an integrated testbed with PTP and SyncE high-precision test capability is essential, as shown in the figure below.
The synchronization requirements of 5G are significantly harder to meet than previous mobile generations. This means a new generation of equipment is necessary to support the requirements and verify they’ve been met.
5G synchronization challenges drove the development of Spirent Paragon-neo. To satisfy the high accuracy and high-rate requirements of 5G, it delivers sub-nanosecond performance for PTP and SyncE testing at rates from 1G to 100G, with integrated test options for ITU-T requirements such as for fronthaul boundary clocks.
Paragon-neo is a fully integrated synchronization testing tool, enabling the generation and measurement of PTP to sub-nanosecond accuracy, with integrated ITU-T stimulus and response test cases.
Assuring the promise of 5G
Precise, defined and repeatable synchronization testing at new levels of accuracy will be key to enabling the promise of 5G. Leveraging our deep involvement in the development of the ITU-T 5G synchronization standards, Spirent Paragon-neo delivers that capability now.
As fronthaul technologies evolve and advance, Spirent and Calnex will continue to offer 5G timing synchronization solutions so operators can fulfill the performance promises they have made to their customers.
Learn more about solving the timing challenges of 5G with Paragon-neo.
Guest contributor: Tim Frost, Strategic Technology Manager, Calnex Solutions
Calnex Solutions is a leading provider of R&D test solutions for telecom synchronization technologies, with a presence in more than 45 countries. Calnex has partnered with Spirent Communications in serving customers in key global markets, including many of the largest telecom companies in the world.