Microtrenching as a means of deploying fiber for distributed antenna systems

Sept. 1, 2017
Service providers are taking a second look at this fiber-deployment method, which enables faster installations, minimizes disruption, and offers long-term savings.

By Scot Bohaychyk, Clearfield

Imagine closing a lane of traffic in a busy downtown urban center for a week? Huge headache.

Yet, when a new fiber communications line is needed in a cityscape of sports and entertainment venues, or a fast-paced business district surrounded by parking lots, service providers may be faced with the choice to close streets or redirect traffic (not knowing there is a better option) as they dig wide trenches to deliver new fiber broadband services. The cost of getting new service to where it is needed is also a major consideration due to the expensive labor and construction costs, which can eat up to 70 percent of the overall budget. Despite the challenges, the need for the service isn’t any less and it can take an extensive amount of time for these projects to become cash-flow positive, giving service providers pause as they weigh the revenue potential.

While these challenges may be a non-starter for some service providers, there are ways to mitigate these risks by using installation techniques and tools that allow for minimal disruption and damage, while speeding up deployment time to turn on new services.

Point-to-multipoint DAS

From the delivery driver that needs to upload manifests and invoices in real-time, to a consumer using location-based services to find a restaurant for dinner while calling an Uber, in dense urban areas, the need to multitask requires high-bandwidth capacity. In general urban areas also have a smaller footprint so the limited space won’t allow for a new antenna to go up in a city park to boost bandwidth. A situation like this calls for a distributed antenna system (DAS) to provide communication paths from a single location, expanding out to multiple locations to ensure voice and data connectivity.

A DAS is a network of antennas that sends and receives cellular signals on a carrier’s licensed frequencies and can be deployed indoors (iDAS) or outdoors (oDAS). Stadiums, arenas, airports, parks and other hotbeds for high-capacity bandwidth would benefit from a DAS environment. If a fiber installation project takes place outside and you need to move horizontally to navigate streets, sidewalks and bridges, or if your install is inside where vertical navigation takes place around concrete walls, floors, and rafters - all of these scenarios present challenges that interfere with connectivity. In addition, urban settings have antenna sites that are commonly situated in or on structures that are encased in concrete. So, finding a way to cost-effectively navigate the hard surfaces to install fiber with the least disruption to surrounding vehicle or pedestrian traffic, while also being able to restore the area in the event of a later fiber cut, requires installation methods that allow the best way to deliver fiber.

Traditional vs. microtrenching

Traditional methods for installing fiber are open trench or directional drilling. Both methods are expensive and time-consuming and may require large machinery taking up space on a busy street that can create chaos for pedestrian or vehicle traffic.

In an open trench application, where the installer must manipulate a hard surface area such as a city street, the pavement or concrete must be cut in two places at least one foot apart. The smallest width for an excavator bucket is 12 inches. The installer then has to break out a one-foot-wide trench and protect the surrounding area and people from falling into it. This can be done with extremely heavy steel plates or barriers, which means blocked access to the area. In an open trench installation, restoral can also take days. Once the installer has removed the top layers of concrete or asphalt and few feet of the substrate and the fiber put in place, all road materials must be returned and compacted to the original solid form factor. It also must be bonded to the surrounding substrate to avoid heaving and moving at a different rate from the surrounding area. An added challenge is the cost of the premium backfill product that has to be purchased, delivered, installed and compacted. Imagine a one-foot-wide, two-feet-deep and 500-foot-long trench. Restoral would take nine passes over the same area to put a hard coat back in place, causing disruption to drivers and pedestrians in the middle of a major city.

Shown here is the Ditch Witch MT12 microtrencher in action. The company explains that the microtrencher “cleanly slices asphalt or concrete to create the ideal trench in one quick, efficient pass.”

The directional drilling method can be less invasive at times, but the installers go in blind and cannot see in the underground drilling space. Before drilling even can start, entry and exit pathways must be cut out, excavated and protected. While doing this work, busy streets or walkways are then blocked for days at a time.

Microtrenching, as the name indicates, is a space-saving footprint that results in minimally intrusive, cost-effective and faster fiber installations to environments like the city park or large entertainment venues that previously were not viable for fiber. Unfortunately, for engineers and installers that have been doing fiber deployments for a long time, they may remember that microtrenching earned a reputation for failure that has caused many installers and engineers to cease using this technique. Some of the early microtrenches were restored with either hydraulic cement, standard concrete, or cold patch. This resulted in water ingress and subsequent failure of the trench. Additionally, some of the early microducts used could not withstand the stresses they would encounter, thus collapsing, and causing a failure. With the innovative products available today, both in microduct and restoral material, microtrenching is making a comeback.

The magic’s in the restoral

Today, the real magic in microtrenching is not the cutting of the trench, but in the restoral materials and methods. Many service providers are rightly taking a second look at how microtrenching aids in much faster installs, minimal disruption, easy restoral and long-term cost savings.

Here’s a closer look at the benefits of microtrenching.

Lower costs for key budget items - Typically, fewer people are needed in a microtrench setting, which saves labor cost monies in comparison to traditional methods. In addition to labor, installers can find cost savings of up to 60 percent simply because they don’t need the additional ancillary equipment and personnel on site, added to the vastly shortened installation timeframe.

Hours, not days - Microtrenched products can be cut, installed and restored in an eight-hour shift. Traditional installations usually require three or four days with either full or partial street closures.

Common sense plumbing with microduct - Microduct is another key element that aids in lowering costs and saving time. With microduct, it is simply a matter of getting the conduit from point A to point B, then either pushing the fiber or pulling the fiber into the DAS equipment. If the installer embraced preconnectorized, pushable fiber, they will see an even more simplified and cost-effective solution. The only time traffic may have to be shut down completely is when placing the microduct, which only takes about one minute when crossing four lanes of traffic. This is user experience at its best.

Minimal disruption - A bustling city may have bumper-to-bumper traffic. Microtrenching causes minimal disruption to traffic because the trenches are only about one inch wide, allowing people and cars to drive over them without plating or barriers, which benefits both the installer and the surrounding traffic. Since the majority of microtrenches are one inch or less in width, and between six and twelve inches deep, this makes it ideal for tight downtown areas. Try doing that with an excavator.

With all these benefits, it’s no wonder microtrenching is making a good name for itself again.

The use of DAS is still growing at a phenomenal pace. Another topic for another day is the ongoing conversation on using a DAS over small cells.

The beauty of fiber in microduct is that it is agnostic so installers can get the same benefits in either environment. As long as customers continue to rely on smartphones and tablets, the demand for a good, seamless user experience will ensure that a DAS will always have a place in the network architecture.

Scot Bohaychyk is senior applications engineer in the carrier group for Clearfield (www.seeclearfield.com).

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