Got Juice?

When AT&T Wireless Services was testing its first digital network in Florida back in 1992, it got more of a test than anticipated. Just as the system was turned on, Hurricane Andrew ripped into the area. Many cell sites went dark because there was no power backup or the backup was limited.

"Out of that lesson, we began to supply alternative systems, which could include gasoline-powered generators as well as traditional batteries," said Ken Woo, AT&T Wireless communications director.

It was a lesson well learned. During the Los Angeles earthquake a few years ago, AT&T averted a catastrophic failure in its L.A. system. The only sites that failed were those inaccessible to the technicians, and those only failed due to the loss of secondary battery power, Woo said.

Power is something you cannot take for granted.

"The power supply is the heart of the system," said Thomas Horton, president & CEO for WirelessNorth Technology Services Group, a subsidiary of PCS carrier WirelessNorth. "You can have the best BTS and technology that money can buy, but if you don't have the ac power to run it or the dc power to back it up when the ac fails, then you have no system."

Mike Loucy, Sprint PCS director of national site development, feels much the same way.

"The primary objective of our network is survivability," Loucy said. "We want to make sure our network is available to our customers, not just day to day, but in times of emergency as well."

In fact, Sprint PCS puts areas subject to weather emergencies -- earthquakes, hurricanes and tornadoes -- into a special class, and on-site independent power is made available in the form of backup batteries, generators or both.

GETTING THROUGHFor WirelessNorth, powering a cell site starts with the site location. If the power fails in Fargo, ND, during a major blizzard, technicians have to be able to reach the sites. Planning for road access and snow remo val ensures that 4-wheel-drive vehicles can get through.

WirelessNorth -- which covers 110,000 square miles in Iowa, Minnesota, North and South Dakota, and Wisconsin -- also does not put its site equipment into small cabinets.

"Up here, with the severe changes we have in the climate, we felt it was best to go with a regular, full-size shelter," Horton said.

The carrier is using +24V, 900A, modular power boards for its sites. Within the power board are three plug-in rectifier modules. Each module carries 33.33% of the total load of that rectifier. If one module fails within the rectifier, the other two pick up and run at 50%; if two fail, which has never happened, one can carry the entire load at 100%.

"When the alarms go off, that tells the NOC (network operations center) that one of our modules has dropped," Horton said. "We dispatch a tech out from the NOC who removes the module, inserts a spare module and brings the system back down to the 33% level. So we have a N+1 redundancy on the modular part of the rectifiers."

Batteries at the sites provide eight hours of backup if the ac power fails; generators back up the batteries. All WirelessNorth shelters have generator-set receptacles, so technicians simply have to hook up a generator to recharge the batteries in four hours.

"We're gambling that the power won't go down over the complete BTA, so we can leapfrog the gen sets in order to make sure that each site stays charged," Horton said.

NOT CREATED EQUALPicking the right batteries is crucial.

Dave Lesser, Yuasa director of integrated systems and services, said some carriers think a battery is just a battery.

"If you're in Phoenix, and it's 120* outside and 180* in your cabinet, and you think a battery is just a battery, it's probably going to die pretty quickly," he said.

In selecting batteries, Horton said he made up a matrix with pros and cons for various suppliers including products, pricing and available lead times. He also relied on his past experience in the industry.

"I knew whose batteries had leaked and whose hadn't," he said.

At Sprint PCS, all power equipment goes through a rigorous analysis before it is approved for use, Loucy said. This includes looking at the vendors' literature and test results as well as testing in Sprint's labs.

"It's driven by a combination of the cost and the reliability of the vendor and the equipment," Loucy said. "If we purchase to meet a survivability objective, we make sure it meets that objective. If you always go with the lower cost, you don't necessarily meet that objective. We found that out."

VENDOR SOLUTIONSBut smaller carriers don't have the testing facilities of a Sprint or an AT&T. In many cases, they rely on their infrastructure vendors for power solutions. In Montana, 3 Rivers Wireless is launching its fifth market. It uses a Nortel CDMA DMS 100 dual-load switch to serve both its wireline and wireless customers.

"Most of our sites are going in core metropolitan areas, cities where power is not so much a risk," said Ernie Peterson, general manager. These cities include Billings, Butte, Great Falls and Helena. "We've elected to go with a minimal battery backup at this time," he said, adding that 3 Rivers has a limited number of standby generators and can rent others quickly when needed.

Michael Kletchko, Nortel Networks senior sales executive for public wireless, said in outdoor enclosures (cabinets), power rectifiers and battery backup is provided. Standard backup in a base station is one hour, which can be upgraded to four hours in the cabinet. In an indoor enclosure or shelter, power is an option, and Nortel will work with the customer to provide what is needed.

The fourth smallest BTA in the nation, with 36,000 POPs, is McCook, NE. Here D-block carrier Pinpoint Communications is turning up its first four sites, though it has not yet gone commercial. Pinpoint selected AirNet's GSM infrastructure for its system after reviewing several alternatives and finding AirNet the most economical, according to Roger Hoffman, Pinpoint executive vice president. With AirNet, one base station can serve up to 10 AirSites, and no T1s are required for backhaul.

"Our AirSites are remote sites powered by 110V," Hoffman said. "We are equipping them with uninterruptible power supplies providing about 11/2 hours of standby. At that point, we would transport a portable standby generator to the sites, which are relatively close."

The base station is located within a building, not in a cabinet, and contains battery racks, chargers and a standby generator located on the building itself.

Hoffman looked at solar power for the system, but concluded it would be too expensive, though it might be a solution for the 370W AirSites.

SITE MONITORINGPinpoint just signed a contract with AirNet for nine more sites. No decisions have been made yet on how the sites will be monitored, though monitoring is part of the plan.

"We will have techs and a monitoring center," Hoffman said. Both Pinpoint and 3 Rivers have the advantage of using techs from their wireline operations to help monitor the cell sites. Peterson said 3 Rivers is using the capabilities of its Nortel switch to monitor the alarms indicating ac or dc failures. The switch is monitored 10 to 12 hours a day, and technicians are on call the rest of the time.

"Even technicians that are not on call get every page," Peterson said.

All WirelessNorth sites are alarmed and linked to its NOC, which is monitored 24/7.

Sprint PCS monitors its power supplies 24/7 from its National Operations Control Center in the Kansas City area. Sprint has conducted a major review of its system since it was laid out three years ago.

"We have survived. Actually last fall we had some significant storms and weathered them with no significant outages," Loucy said.

Horton is moving into Phase II of the WirelessNorth build-out and said that the power-supply system is one of the few things that it hasn't changed.

His service group also works with small C-, D-, E- and F-block players, consulting and providing engineering expertise in their design and build-out.

"We can teach them how to cut costs in the build-out without sacrificing quality," he said. But when Horton is discussing costs, he always makes one point: "If you are going to cut costs anywhere, don't cut costs on your power supplies. It's a big gamble."

Are you in the market for dc power equipment? Chris Searles, Yuasa Energy Products Group product & marketing manager, suggests you ask these questions about the supplier and product:

1. Does it offer state-of-the-art features that simplify the installation and serviceability, thus reducing the installation time and costs?

2. Does it provide enhanced operating features at standard cost that will optimize performance in the new network's demanding applications?

3. How simple is it to follow the documentation when installing a power plant?

4. What type of service, maintenance and support factors does the supplier of the dc power equipment provide?

5. What kind of warranty does the supplier provide for its equipment?

FEATURETemperature hardening of rectifiers and converters.

BENEFITEquipment performs at full capacity without derating from -40*C to +65*C (-44*F to +149*F); permits full performance of equipment in non-environmentally controlled installations.

FEATUREActive power correction.

BENEFITGreater power efficiency. Elimination of ac harmonic disturbances.

FEATURETemperature compensation.

BENEFITEnhances battery life and mitigates thermal runaway.

FEATUREEMI FCC Class B Rating.

BENEFITLower EMI. Less interference with RF and other sensitive equipment. Acceptable in residential environments.