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Reader Forum: In-building DAS – cost savings with pushable fiber

Editor’s Note: Welcome to our weekly Reader Forum section. In an attempt to broaden our interaction with our readers we have created this forum for those with something meaningful to say to the wireless industry. We want to keep this as open as possible, but we maintain some editorial control to keep it free of commercials or attacks. Please send along submissions for this section to our editors at: dmeyer@rcrwireless.com.

DAS is an exciting technology as it allows for greater usage and bandwidth transfer in heavily populated areas. Whether building outdoor DAS or in-building DAS, fiber serves as the building block to a successful DAS implementation. With outside DAS, service providers face hurdles such as running fiber to antenna sites that are commonly situated in or on concrete- encased structures.

With in-building DAS, challenges extend to seamlessly integrating multiple technologies. Pushable fiber technology teamed with fiber management best practices will ensure the performance requirements of each of these environments while reducing the cost of such implementations.

Pushable fiber is just what it sounds like – fiber that can be pushed. One to 12 250um fibers can be placed in a 3-millimeter jacket. The jacket is constructed of an extremely durable, flexible, crush proof HDPE material that is manufactured to prevent any bend radius violations, thereby protecting the fibers inside. This pushable fiber is then placed and “pushed,” most often by hand, through 10-mm ruggedized microduct that has been previously placed. Both the ruggedized microduct and pushable fiber materials are OSP rugged and will not fold, kink or crush.

Reducing splicing costs

Pushable fiber can be deployed from a remote location and easily installed using typically two technicians. One of the biggest benefits of this system is the ability to pre-terminate one to two fibers on both ends and still push through the microduct as it was intended or to factory terminate up to 12 fibers eliminating half the splice labor.

When a pre-connectorized solution is used in a single fiber application, there is no need to dispatch a splicer to make the final connections. A basic installation technician can make the terminations and plug in the customer in about 30 seconds. Taking this into account, two set ups are saved for the splicer (one at the street connection point, and one at the customer end). Given that a reasonably good splicing technician will need on average 30 minutes per end to set up, prepare the fiber, splice and tear down, at a loaded rate of $100 per hour, you have to add a $200 cost to each drop deployed. From a personnel perspective, there are usually many more installation technicians available than there are trained splicers and in using a pre-connectorized solution, virtually anyone from the summer intern to the receptionist can be trained to install the connector in just a few minutes. On multiple fiber solutions it is possible to eliminate 50% of the splicing on counts up to 24 fibers. This method only requires splicing on one end of the fiber (typically the street end).

Pushable fiber makes micro-trenching possible

Traditional trenching is an expensive and labor-intensive process. It has become such a sore spot in the deployment of cable that even Wikipedia has gotten into the act, providing a 14-step process on how to plan your excavation. Challenges associated with soil types have been well documented, as well as the laborious steps associated with creating the support structure to prevent cave in, dewatering and/or benching the excavation.

The traditional trenching method of digging a one-foot wide trench, placing a two- to four-inch conduit, backfilling with concrete and then repaving is long gone. This older method typically costs upward of 60% more to do, and also impacts the local traffic in ways that just are not acceptable anymore. With the pushable fiber method of micro-trenching, a slot is cut, usually at night, and then two microducts are placed in the slot. One of these microducts typically has the ability to be located. This is critical, as when fully restored, it’s virtually impossible to see where the trench is and after a season of resurfacing, it will be fully invisible.

Micro-trenching is a far superior alternative and is the ideal manner as it is less time consuming, less invasive and allows for traffic to pass over the trench line without worry of causing damage. The trench width is usually one-inch or less, and since less material is removed, it can be easily restored. After the microduct is placed in the trench, a small hole is bored into the manhole where the fiber ring is located. The microduct is placed into the splice case, just as a traditional cable would be, then the fiber is simply pushed through the microduct and spliced as a normal cable.

Reinforcement of an existing duct structure

When the requirement is for fiber reinforcement in an existing duct structure, such as rooftop sites, there are some common threads: The lack of space and the costs associated with constructing new pathways through the riser space in buildings is just as prohibitive as digging up city streets.

Pushable fiber addresses this much in the same manner by installing microducts inside the existing structures to provide a distinctive pathway and using the pushable fiber, simply by pushing the fiber from the top down. The added benefit of installing in buildings is gravity. Given the small size of the pushable fiber, we can easily carry it to the top floor and let gravity help with the installation.

A recent installation provides a great example. There was a one-and-one-quarter-inch innerduct installed from the building to the manhole previously, so that path was established. The challenge was that the one-inch conduit already had four Cat5 cables and a 25 pair telco cable in it. Additionally, there were a total of 22, 90-degree sweeps in the route. First, two 10-mm microducts from the rooftop hut to the equipment room were installed, followed by coupling on two microducts that were pushed through the one-and-one-quarter-inch innerduct to the manhole. After installing the microducts, the fiber was pulled from the rooftop to the equipment room in one pull through 22, 90-degree bends. After that, it was a simple pull to the manhole.

Why pushable fiber?

While the need for fiber is clearly demonstrated at DAS antennas, the cost-effective means to delivering that technology is less understood. In the examples given, pushable fiber and microduct solutions, when combined, not only saved money for the carrier, they lessened the impact on the people that are being better served by the installation. Our goal is getting the most fibers to the site with the least amount of personnel and equipment. The less people and equipment that is needed, the least cost associated with that particular deployment. Balancing this cost with deployment of the right amount of fiber to future-proof DAS projects is an important consideration.

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