Don’t Let 5G Sink Your Network’s Timing & Sync
5G Challenges Current Timing & Sync Standards
Investment in the mobile ecosystem is driven by seemingly insatiable consumer demand for mobile bandwidth. Supplying it to them is arguably a great business to be in. Mobile operators will continue to compete for market share by deploying 5G for more bandwidth capacity, and adding more radio towers (including small cells) to improve network coverage. The irony is that unless the network is properly synchronized the combination of 5G and more radio towers, two positive things in isolation, will actually work against each other. The out-of-sync tower signals will interfere with each other, calls will be dropped, packets will be lost, videos will be interrupted, and self-driving cars will become self-crashing cars. Poor timing and synchronization will become the new source of customer churn.
Older generations of mobile technologies only required frequency synchronization to align signals. New technologies, including 5G, have the same frequency requirement but also have phase and time requirements in addition to frequency. Clearly, frequency sync alone will no longer meet the more stringent demands.
Mobile operators can address the more stringent timing and sync requirements of 5G in a couple of ways. The easiest way is to simply equip each mobile base station with a GNSS receiver, and then lock into multiple satellite signals to make the precise time calculations. Many carriers use this method today with satisfactory results, and it will suffice with 5G also. However, there are some concerns.
First, there is a line-of-sight issue. Not all base stations will have access to multiple satellite signals needed for accurate timing. Obstacles like trees, tall buildings, construction cranes, billboards, etc, block those signals, especially in densely populated urban areas, precisely were more base stations and antennas are needed. This problem can be solved by placing a receiver on a rooftop, above the obstacles, but that’s not feasible in every case.
Then there’s the inherent vulnerability of GNSS signals, even without physical impediments. The signals are weak at the earth’s surface and are easily interfered with. Though usually discussed in the context of positioning systems, such things as GPS jammers and spoofers, atmospheric interference, multi-path from reflected signals, radiation from malfunctioning electronics, or simply severe weather damaging an antenna installation are common causes for failure. These vulnerabilities are acceptable when the application is watching a cat video on YouTube, but when the network is relied upon to deliver low-latency signaling to self-driving cars those weaknesses become, well…scary. From a market share perspective, even cat videos crashing out is not something mobile operators want their customers to experience.
In theory, an operator could install a high-qualify holdover oscillator at every base station, such as a rubidium miniature atomic clock, to serve as a timing source when GNSS signals are lost. However, with so many small cells needed to cover cities, and with the number of devices that need connectivity growing daily (Internet of Things), cost becomes the prohibitive factor.