LMDS gets another day in the sun

New approach improves capacity of base-station technology
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The successful deployment of video and data services using LMDS (local multipoint distribution service) has met with more failure than success during the past 15 years, but Portugal-based SGC Telecom is looking to tip the scales the other way.

The wireless-broadband operator and technology company has worked with Lockheed Martin to create new LMDS high-power base stations that the companies say provide 40 times the capacity of base stations built on solid-state amplifiers.

"It allows us to provide services over a very broad bandwidth so that quality can be maintained across that bandwidth," says Jeffrey Horoshak, Lockheed Martin senior systems engineer, network systems development.

LMDS uses wireless base stations to transmit and receive microwave radio signals within a set geographical area. The transceiver device used by the customer has a fixed location; typical configurations call for a transceiver placed on a rooftop for line-of-sight to the base-station transceiver.

According to SGC Telecom CEO Miguel Martins, the technology will allow local exchange carriers to offer customers a triple play of voice, video and data services. The system is currently being rolled out in Lisbon, Portugal, where customers will have access to phone service, 36 channels of video, and data bandwidth of 2 Mb/s in early 2003. Video-teleconferencing capability is also in the mix of services.

"In our view, there's a big gap between broadband demand and broadband offerings," Martins says. "There are a lot of people waiting to be served with always-on broadband access. At the same time, there are companies ready to provide content. But there's a bottleneck in the middle, which is the local loop. We've found a way to relieve that bottleneck."

What differentiates it from previous LMDS offerings is the use of traveling-wave-tube amplifiers (TWTAs) in the base station instead of solid-state amplifiers (SSAs). SSAs are capable of 0.1 W in linear power output; TWTAs generate 8.15 W. As a result, the TWTA base station can serve 50 square km and up to 25,000 customers, numbers that give LMDS the type of coverage that can create business opportunities. An SSA base station could serve only 9 square km for the same type of multicarrier architecture.

"The problem has never been the technology itself," says Martins of LMDS. "But it was working based on system parameters which weren't large enough to promote a business model that could work."

Lockheed Martin is working as a technical adviser and system integrator with SGC Telecom. The companies have worked together for 18 months in developing the technology. For the Portuguese deployment, the system is designed to offer six TV carriers, 21 downstream data carriers and 54 upstream data carriers. Each 8-MHz TV carrier can handle six TV channels (using OFDM modulation), and the data carriers offer 27-Mb/s data downstream and, potentially, 4.6-Mb/s data upstream.

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