Wireless Systems Design

Coverage Moves Underground

No matter how pervasive wireless networks have become, they still can't provide coverage everywhere. People assume that "everywhere" is an umbrella term for places with smaller populations. Yet people in urban areas have their share of complaints too. In fact, it seems that big cities suffer from almost the same amount of problems as remote areas. For instance, wireless services usually cut out in tunnels. To the major cities that house subways, this means that users cannot use their handheld devices while riding on the trains or even while they are waiting for them. To improve this urban coverage problem, Allgon Telecom Ltd. (www.allgon.com) and Aldridge Electric, Inc. are deploying the first multi-carrier, multi-technology wireless coverage system for a U.S. subway.

The companies will provide a comprehensive wireless-telecommunications coverage solution for the Chicago Transit Authority (CTA). The solution will cover its rapid subway tunnels, underground stations, and station passageways. The CTA operates the nation's second-largest public transportation system. It covers the city of Chicago and 40 surrounding suburbs. On an average weekday, 1.5 million rides are taken on the CTA.

To provide these riders with wireless coverage, the solution will rely upon Allgon's fiber-based distributed-antenna network. This antenna network will transmit mobile radio signals from strategically positioned radio base-stations housed outside of the Chicago Subway tunnel system (see figure). The multi-provider and multi-band system of repeaters and antennas will be connected to a common fiber-optic backbone—a solution that hails from Allgon Coverage Engineering (ACE).

The ACE team is a group of RF and systems engineers who specialize in delivering turnkey solutions for complex environments. They have provided coverage in obstructive environments worldwide, such as subways, airports, road tunnels, railways, bridges, shopping centers, and mines. By incorporating flexible, modular products, the ACE team ensures that its systems can evolve along with future technology and needs. It then backs up these systems with ongoing operation and maintenance capabilities.

This approach has successfully taken Allgon through a number of subway projects. To name a few, they include the Berlin Subway, Santiago Metro, Moscow Metro, Taipei TRTC, Valencia Metro, and Sweden's Railway Söderhamn. Yet this current project will be the first state-of-the-art, multi-provider, multi-technology wireless-coverage solution deployed in a U.S. mass-transit system.

The 18-month installation is expected to commence immediately. In seven to nine months, limited service throughout the two 11.4-mile tunnels should be available to carriers. The system will support all major U.S. wireless providers. At the same time, it will enhance the communication system for the Chicago Transit Authority, Chicago Police Department, and Chicago Fire Department/EMS.

TAGS: Mobile
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