Distributed Antenna System (DAS) Case Study:
Boston Subway (MBTA)
THE PROJECT: Phone Coverage in the Boston Subway In late 2004, the Massachusetts Bay Transit Authority (MBTA) decided it wanted to provide continuous, end‐to‐end cell phone coverage in the underground stations and tunnels of its transit system for its riders. InSite Wireless, LLC, a company specializing in the design, construction, operation, and maintenance of shared wireless infrastructure for complex indoor environments, bid on the project – and on May 31, 2005, as a result of the public bidding process, MBTA awarded InSite a contract What is DAS? to provide and operate a neutral host wireless distributed antenna system (DAS) in The DAS acts like a radio tower, with the subway system. special adaptations to transmit and receive signals underground. Instead of broadcasting radio signals to cover a broad geographic area from antennas mounted on a tower or building rooftop, the DAS converts radio signals to light using lasers and carries the signals to remote locations using fiber optic cable. Equipment at the remote locations converts the light signal back to radio, amplifies it, and transmits it through an antenna system. The term “neutral host” means the system provides access for all wireless carriers over common equipment. Phones, PDAs, and wireless modems communicate with the underground antennas to complete phone calls and data sessions. THE CHALLENGE: InSite had to design a system to accommodate the varied geometry of the tunnels and the different types of trains used on each line. When space to mount the equipment was not available, or where difficult geometry (like long curves) limited signal propagation, or both, InSite’s engineers had to look for an effective alternative to the usual antennas. Additionally, InSite had to work around the massive flood gates near South Station on the Red Line—huge doors installed during the Big Dig that allowed the MBTA to seal the Red Line tunnels at South Station and Broadway to prevent water passage during the construction of the Big Dig highway tunnel where it crossed the Fort Point Channel. If highway construction penetrated the subway tunnel by accident and water from the harbor flowed in, the gates would prevent the entire subway system from being flooded. InSite needed a way to get cable past those gates to the rest of the tunnel without interfering with operation of the gates. THE SOLUTION: 
Walking the Tunnels. The design team walked the entire length of the tunnels at night when the trains were not running to understand the layout and identify any special considerations that might block signals, like large pipes or conduits crossing the tunnel or running along the wall. 
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Testing and Gathering Signal Data. InSite also installed test antennas to transmit test signals and rode trains to capture actual received signal levels on specialized test equipment. The test teams also measured the pre‐existing signal levels on trains and in stations to identify how strong these “background” signals were—since the system is designed to pick up where the outdoor signals leave off. With data in hand, the design team identified exactly where to place the remote amplifiers and antennas in the tunnels. Creative Problem Solving. To solve problem installation areas and along the longer curves, the designers specified radiating cable instead of antennas. Radiating cable is regular antenna cable with slots cut into the outer conductor in such a way that the cable works like a sprinkler hose to “spray out” low levels of signal along its entire length. To work around the flood gates near South Station, the InSite team used cable sleeves through the flood wall beside the gates to pass the cable into the rest of the tunnel and provide wireless service while staying clear of the flood gates in case they are needed in the future. InSite Wireless, LLC ‐ A Division of InSite Wireless Group, LLC – www.insitewireless.com Distributed Antenna System (DAS) Case Study:
Boston Subway (MBTA)
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Project Team. Powerwave Technologies performed the RF system design and provided the fiber optic DAS equipment. Dewberry‐Goodkind, Inc., the Architect‐Engineer on the project, prepared construction drawings for MBTA approval. Electrical contractor Sullivan and McLaughlin, known locally as Sully Mac, installed the Powerwave equipment along with fiber optics, power, and antennas to complete the system. After installation was complete, the entire system was tuned and tested to assure that it met the established performance criteria. THE RESULTS: 
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December 2007—Phase I was launched with T‐Mobile, AT&T, and Verizon providing service in the downtown core of the subway. The initial 8 stations included Park Street, Downtown Crossing, State Street, and Government Center, as well as all connecting tunnels. March 2010—InSite Wireless completed expansion of the DAS to provide coverage on the MBTA Orange Line from the tunnel entrance south of Community College to Massachusetts Avenue, specifically North Station, Haymarket, Chinatown, New England Medical Center, Back Bay, and Massachusetts Avenue. T‐Mobile is now operating its 2G and 3G service and AT&T will be launching 2G and 3G service within the next 30‐60 days. Current technologies supported:  all current 2G and 3G technologies  800 MHz cellular, 1900 MHz PCS and 1700/2100 MHz Advanced Wireless Services (AWS) Future technology capabilities:  Future 4G technologies  4G Long Term Evolution (LTE) on 700 MHz  WiMAX at 2.5‐2.7 GHz SYSTEM BENEFITS: 
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For MBTA: Installation of the DAS provides MBTA more than $4 million dollars in non‐fare revenue in the initial contract term. For InSite Wireless: InSite deploys the DAS and charges participating wireless carriers to use the system to cover payments to the MBTA and operating expenses, while maintaining a steady recurring revenue stream. For Carriers: The DAS provides an increase in customer usage thanks to the customers’ ability to use the service underground. For MBTA Riders: The InSite DAS provides continuous service in stations and in trains, allowing riders whose service providers connect to the antenna system to text, make phone calls, check email, and surf the web while on the subway. Callers can place a call above ground, carry it underground, and continue the call until they finish. For the Community: Wireless service underground enhances public safety and security by allowing commuters to report safety related concerns or security matters while waiting on platforms or riding trains. It also promotes use of public transport. NEXT STEPS: The underground portion of the Red Line in Boston will be completed in spring 2010 (serving South Station, Broadway, and Andrew stations.) T‐Mobile and AT&T will be operational on both 2G and 3G upon launch. The expanded system will allow a rider to hold a conversation from the Longfellow Bridge to Braintree. By mid‐2010, the DAS will include: 17 stations, 9 miles of tunnels, 42 remote amplifier locations, 212 antennas, and more than 12,000 feet of radiating cable. InSite plans to continue construction until the entire subway—including all 34 underground stations and 19 miles of connecting tunnels—have seamless wireless service with expected completion in 2011.
About InSite Wireless, LLC InSite Wireless specializes in the design, installation, operation, and maintenance of shared wireless infrastructure solutions that enhance the quality and capacity of wireless voice and data services in public facilities and complex environments. InSite built and launched its first DAS at the Moscone Center in San Francisco in 2001, and has developed and currently operates additional projects in convention centers (including the Boston Convention and Exhibit Center), casinos, airports, sports stadiums, and transit systems like the MBTA subway system. InSite’s parent company, InSite Wireless Group, LLC, also owns InSite Towers, LLC, which develops, manages, and owns more than 350 telecommunications towers and sites for wireless carriers. InSite Wireless, LLC ‐ A Division of InSite Wireless Group, LLC – www.insitewireless.com