Source of Synchronization in Wireless Networks: Laying the Groundwork for 5G

Along with my Microsemi colleague, Jim Olsen, we were recently the guest speakers on an RCR Wireless News webinar speaking on 5G network densification and ways to prepare your timing architecture. Over the next few days, I will share some thoughts on the topic including the challenges of network timingservices for 5G networks that operators must consider including the key concepts of setting, maintaining, and holding phase.

The source of sync for all the wireless networks is GPS; this is really the source of time traceability. The GPS networks of satellites carry very accurate clocks and this is the way to establish time and phase synchronization traceability to universal coordinated time, or UTC. GPS is the workhorse for synchronization; that’s the source and then it generates not only the time and phase, but also the frequency.

The clock needs to be distributed out to the endpoints so you have a good core source clock. Then, you distribute it, inject it into the network. The operator then carries it across their transport network; this is the backhaul and evolves into the fronthaul networks. And, to carry all of the traffic, it also carries the clock timestamps out to the end application where you have a small clock to recover that clock.

Now, along the way, there are little errors that build up. There are things like jitter and asymmetry, but the end clock filters all of that and then holds the application-specific requirements, which are getting tighter and tighter. You also see the option at the end clock to put GPS in that location. In many cases, the GPS is already available with a line of sight to the sky so you can lock the end station with the GPS signal. Then you’re using a network lock for your backup and to hold over in the event that the local clock is lost.

The trend we’re seeing moving forward, however, is that the end clocks are coming becoming ever denser with the increased use of small cells everywhere and since they’re going in indoor locations, they’re without line-of-sight to the sky and unable to use GPS. So increasingly, the end stations will need to rely on the source clock coming across the network for their time and frequency synchronization. This gives rise to a lot of standards work that is being done to engineer how the transport network will carry the source clock out to the end stations.

Speaking of standards, my next article will speak to the standards that dictate where the time comes from and standards that the industry is adopting.

Connect with me on LinkedIn, I welcome your thoughts and comments on this topic.

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