The pressure on telecoms operators to accelerate the 5G rollout is building up and it’s time to address a key challenge - 5G synchronization. Time synchronization is a mission-critical service in all 5G networks. Providing accurate time and phase synchronization to the cell tower is key for efficient and secure 5G deployment and operation. 5G services cease to work without synchronization, while a faulty synchronized base station could interfere with the 5G operations of other operators as well as connected services and use cases.
The time accuracy requirements are much higher in 5G networks than in 4G because of the increased use of Time Division Duplex (TDD). New 5G features such asmassive MIMO and the requirements from new services such as eMBB, mMTC, and uRLLC also stipulate high accuracy timing support. As a result, the cost and complexity of 5G time synchronization increase and it puts high demands on the underlying network infrastructure.
Operators have a range of options to consider. GNSS/GPS and Precision Time Protocol (PTP) solutions deliver the time and phase synchronization mobile networks require but suffer from serious vulnerabilities. Luckily, innovation in 5G synchronization means more solutions are available to enable operators to roll out 5G confidently, securely, and cost-efficiently.
The time synchronization solution landscape
GNSS/GPS solutions provide highly accurate time synchronization in mobile networks. However, they also have significant downsides where the weak nature of the signals means that any form of RF interference can cause severe disruptions to the GNSS service. Recently, geopolitical tension has made operators aware of the vulnerability of the GNSS solution with satellite signals easily jammed or spoofed, causing 5G operations to be disturbed and even ceased.
Therefore, several countries have mandated that all 5G deployments be GNSS-independent for the operator to receive a license..
On the other hand, network-based time synchronization solutions based on the PTP, or IEEE1588, standard have become the primary synchronization solution for 5G networks - often complemented with GNSS for resiliency and performance improvements. However, to achieve the accuracy requirements, PTP installations require full on-path support, i.e., every network node and line card from the master clock to all base stations needs to support FTS (Full Timing Support) of the Precision Time Protocol (IEEE1588 PTP). This forces mobile operators to replace or upgrade a large part of their existing IP and optical infrastructure, significantly increasing the cost and complexity of deployments, especially in regional and rural areas. For some operators, this investment and operational costs for this are unsustainable, which means certain areas risk lagging in the 5G rollout and its benefits.
Overlay time synchronization changes the 5G game
5G is not simply a connectivity network for voice, video, or data (eMBB) - it drives new business opportunities for organizations across industries and spearheads digital transformation in society. By separating network functions, using open Interfaces and APIs, etc., third-party developers and service providers will be able to design innovative solutions and enable modern DevOps methods. In the same way, it is desirable to disaggregate the 5G synchronization function from the hardware infrastructure, as required in PTP FTS solutions, and instead offer time synchronization as an end-to-end overlay services. Such an open overlay synchronization solution is cost-efficient and brings unique advantages. It is independent of network architecture andvendor agnostic. An overlay solution can be combined with current PTP FTS solutions and be deployed in parts of the network to secure and accelerate 5G rollouts, especially to rural areas but also for e.g., Mobile Private Networks (MPN).
Overlay synchronization solutions that meet the timing requirements of 5G TDD over existing IP/MPLS and DWDM networks remove the need for expensive network upgrades. The solution creates an overlay synchronization network that scales to thousands of time nodes. It includes built-in mechanisms to handle link, node, and clock failures as well as changes in asymmetries in underlying networks.
One challenge in overlay synchronization solutions is the packet delay variation (PDV) that the timing information experiences when switched over an L2VPN or L3VPN. Where PTP with Full Timing Support goes to a considerable effort to remove the PDV in every node, overlay time synchronization solutions can instead use methods to manage and mitigate the effects of PDV and, therefore, can transfer time over multiple network nodes without PTP FTS support.
These solutions include an intelligent synchronization routing protocol with inherent redundancy and holdover support in case of link or node failures in combination with dynamic sync packet rates and intelligent filtering. The other challenge to handle is asymmetries. Static asymmetries can be easily compensated through static offsets, but overlay solutions need to have strong algorithms to detect and compensate for dynamic asymmetries in the networks.
Luckily, 5G network synchronization solutions have a lot to learn from digital terrestrial TV, DVB-T2, and ATSC3.0, networks requiring Single Frequency (SFN) transmission. These networks have similar requirements of a maximum time error of 1.0-1.5 µs as in 5G mobile networks. This means that solutions that have already been trialed and tested in large national DVB-T networks for years can prove critical in resolving the challenges of 5G synchronization.
A cost-efficient route to 5G deployment
Operators are at crossroads - they need to balance the need to speed up 5G rollout with increasing time synchronization costs and the risk of single vendor lock-in. GNSS solutions can offer the time accuracy required by 5G networks. Still, the vulnerability of GNSS/GPS solutions to jamming and spoofing is increasing, which has made both operators and governments look for GNSS/GPS-independent solutions.
Alternative synchronization solutions are based on an open overlay architecture disaggregating the synchronization functionality from the transport. They are GNSS/GPS-independent and meet the strict time synchronization requirements for 5G deployments, including TDD and Massive MIMO.
Overlay synchronization solutions benefit from being open and working over existing infrastructure without requiring a complete network upgrade or replacement of nodes. They use unique asymmetry detection and compensation combined with jitter smoothing mechanisms to enhance synchronization performance. They have been validated in action, as media companies have deployed them in the media industry to meet stringent reliability and time synchronization requirements for single-frequency digital TV networks.
These innovative solutions significantly reduce the CAPEX and OPEX in new 5G rollouts, especially for incumbent operators (i.e., brown-field operators). They can also reduce rollout times by bringing time synchronization to 5G RANs over existing transport network infrastructure.
It’s time for operators to take advantage of the innovation behind 5G deployment to drive cost and operational efficiencies that will help welcome the new era of connectivity as quickly as possible.
