Redundant mobile backhaul without network overhaul

The challenge

Redundancy demands across thousands of tower sites with limited fiber

Mobile backhaul connects distributed radio sites to the core network and carries large volumes of traffic across geographically dispersed locations. Because each site serves large numbers of users and signals must travel long distances, failures must be avoided and reach must be maintained across the network.

As the network grew and customers increasingly began to demand redundancy, the tower provider was faced with the challenge of delivering protected 10G mobile backhaul to thousands of tower sites. Every connection needed a protected path, and the design had to accommodate future coherent wavelengths as network traffic grew. Many towers were not yet connected by dark fiber, which made common network architectures difficult to apply without introducing unnecessary cost or operational complexity.

Building new fiber with redundant paths would have required extensive construction and high capital investment at this scale. An active DWDM design using powered equipment at each site would have introduced operational overhead, including power, cooling, and maintenance across hundreds of locations. Passive optical designs were also constrained in this case, as many tower sites were not connected in a way that allowed for protected paths. These challenges made it necessary to find a different approach.

The Solution

An active/passive architecture that removes field complexity

The tower provider deployed a groundbreaking active/passive DWDM solution using Smartoptics open line systems. The innovative architecture delivers high-capacity coherent wavelengths in a compact footprint, while minimizing the need for power, cooling, and space at each distributed site. By centralizing active components and simplifying the field environment, the solution meets all customer expectations for redundancy while staying cost-efficient and easy to use.

“The active/passive mobile backhaul architecture is based on building ring structures and routing the fiber so that each site connects into the ring as a passive node. This means you don’t need any power or active equipment out at the tower locations. At the same time, you dedicate wavelengths in both directions around the ring, so the traffic can flow either way if there’s a fiber break. This gives you protection without duplicating infrastructure or building active sites in the field,” says Kent Lidström, CTO, Smartoptics.

Stable performance with automated wavelength balancing

The tower provider now benefits from a mobile backhaul solution eliminates the need to manually balance signal power across the network as conditions change. Instead of relying on manual attenuation as wavelengths are added or routes vary, the open line system maintains correct signal levels automatically across the network. This simplifies operation and avoids the ongoing effort required to keep large, distributed deployments stable at scale.

“When multiple wavelengths reach the amplifier, some are much stronger than others. If you just amplify them as they are, that imbalance gets worse. What we do instead is flatten the spectrum before amplification so all channels enter at the same level. Then we pre-emphasize the wavelengths based on how far they need to travel through the network, continuously equalizing and pre-adjusting signals as they propagate. That way every signal arrives with the right power at its destination,” Kent explains.

The Result

Cost efficiency scaled across hundreds of rings

The Smartoptics approach significantly reduces both capital and operational costs by avoiding fiber construction and eliminating the need for powered infrastructure at tower locations. The architecture has already been scaled to hundreds of the tower provider’s active/passive rings, meaning the cost savings are multiplied across the deployments.

After starting with large-scale deployment for mobile backhaul, the same Smartoptics open line systems have also been used for other backhaul applications, including business services and broadband networks. Because the solution is based on standard wavelength transport, it can be applied wherever capacity needs to be added over existing fiber to maximize fiber utilization.