Optical Zonu offers ‘GPS at the Edge’ for 4G/5G small cell deployments

The huge current investment in deploying 5G mobile networks is promoted by setting high expectations for significantly increased throughput and reduced latency.

This can only be realized by deploying the network radios close to the users, especially for the millimeter-wave frequencies with their short propagation distance.

This also means a high density of radios, often imbedded within macro coverage.

To coordinate seamless functioning, network synchronization accuracy must be much higher than with legacy deployments, according to Optical Zonu. The greatly enhanced data throughput with advanced features such as aggregation, massive multiple-input/multiple-output (MIMO) and beam steering require highly accurate network timing and phase coordination.

Small cells close to a network’s edge are usually far from the hub where the grandmaster timing server generates the PTP timing signal and sends it to the network edge over the Ethernet backhaul. The long runs require multiple hops through routers and switches. Each of these adds dynamically changing packet delays depending on network loading. Also, there are inevitable asymmetries between the upstream and downstream packet delays. These timing errors can result in a drastically reduced network performance.

One way to correct these timing errors is to connect an edge grandmaster server at the small cell location connected to the local backhaul router. Connecting the GPS directly to each of the small cells is the other way.

The GPS approach is simple in concept, but has been problematic since, with small cells distributed in the facility, many or all the units can be far from a window where a GPS antenna could be mounted.

Optical Zonu, a U.S. carrier-approved supplier of RF-over-fiber transport solutions, has solved this problem with its GPS at the Edge kit. The GPS-over-fiber solution distributes GPS to each small-cell location alongside the backhaul.

A compact GPS fiber antenna unit connects to a GPS antenna on the roof. A single cable connection to this unit provides power to the unit and brings the fiber-optic connection to an optical splitter, which is collocated with the local router for the small-cell backhaul.

The fibers from this splitter are routed along with the backhaul cable to each small-cell location, where they each connect to a small fiber base unit that recovers the GPS signal and connects it to the auxiliary GPS port on each small cell.

Optical Zonu offers two variants.

Small cells with fiber-optic backhaul. Higher power cells typically use a fiber-optic backhaul and require local AC power. In this case, one of the fibers in the cable to each small cell is used for the GPS connection, and each base unit connects to the local AC power with an adapter. In this case, the only additional cable needed is the single run to the rooftop.

Diagram: Optical Zonu

Small cells with a CATx backhaul. This setup is typical for lower power small cells. In this architecture, a single fiber is pulled along with the CAT6 backhaul cable. A single hybrid fiber/CAT6 cable can also be used. The fiber is connected to a small fiber base unit at each small cell to recover the GPS signal, which is connected to the small cell auxiliary GPS port. The CAT6 is also connected to the fiber base unit. The backhaul is passed through from the small cell, and the PoE++ is tapped to power the base unit. Once again, the only additional cable pull is the single run to the rooftop antenna — local power isn’t needed at every small cell location.

Diagram: Optical Zonu

The Optical Zonu GPS at the Edge kit provides an easy-to-install and cost-effective solution that guarantees the highest timing and phase accuracy for a network that is vendor agnostic and, as with the edge grandmaster approach, still has the central PTP as a backup.

For more information, visit Optical Zonu.