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Boston Subway DAS Completed

November 24, 2015

By J. Sharpe Smith

November 24, 2015 — InSite Wireless has completed a DAS covering the Silver Line in Boston, which is the fifth, and final, phase of the wireless deployment across the Massachusetts Bay Area Transportation Authority (MBTA) underground transit system.

The Silver Line DAS infrastructure deployment, which took three months to complete, consists of 1 mile of dual bore busway tunnel, three underground stations, four remote equipment locations, 20 antennas, 24 remote amplifiers, 9,760 feet of radiating cable and one mile of fiber optic cable.

“[The Silver Line deployment] is similar to the subway tunnels, but uses buses to whisk travelers from Logan Airport through the Innovation District to Dudley Square,” Joe Mullin, InSite Wireless Group CTO,” said in a phone interview. “You still have to get access and there is a limited time to go in and get your work done. We ran radiating cable the length of the tunnel, and, as we expanded the system, we had to increase the fiber capacity back to the headend. It all came together quite well.”

When the MBTA set out to equip its subway with wireless coverage in 2005, the Silver Line had not yet been completed. It was part of what is known as “The Big Dig.” The Silver Line was added to InSite Wireless’ original DAS deployment across the Blue, Green, Orange and Red lines of the MBTA, which was completed in 2014.

The total MTBA deployment covers 20.5 miles of tunnel, 38 underground stations, 102 remote equipment locations, 442 antennas, 612 remote amplifiers, 81,215 feet of radiating cable and over 20.5 miles of single mode fiber optic cable.

The subway uses the Solid Titan 20-watt high power product, which can provide coverage and capacity for multiple operators.

“Subways are really fascinating. Buildings and subterranean environments that disrupt the propagation of macrocellular network force you to solve for both coverage and capacity,” said Mike Collado, vice president, marketing, for SOLiD.

In 2008, the subway averaged 598,200 in riders daily, making it the fourth busiest subway system in the United States.

“Subways are very peaky in terms of the ebb and flow of passengers that occur between the trains and buses,” Mullin said. “You address and manage the traffic spikes. People are on their smart phones the entire time they are on the bus or train.”

Boston’s MBTA, which is one of the oldest in the world, was not developed with space for wireless in mind. Where do you put the infrastructure? Base station hoteling can be used for a subway, because there isn’t enough space for the headend gear under ground.

The carriers operate their base stations for the entire DAS system out of a single base station hotel centrally located in downtown Boston, and the Silver Line shares that common headend with the rest of the MBTA.

“[Base station hoteling] is interesting architectural strategy. It is a model that informs potentially how you architect above ground wireless solutions, where you put your headend end in real estate that is less expensive,” Collado said.

Coming up next in the Boston area, InSite will complete a DAS build-out for Amtrak/MBTA Commuter Rail in the Back Bay high-speed rail tunnel later this year.

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