The rooftops of the World Trade Center (WTC) stood more than 1,360 feet over Liberty and Church streets. Their flat surfaces provided plenty of space for wireless and broadcast transmitters. Mounting antennas on top gave carriers a line of sight up to 45 miles. They were considered the best sites in Manhattan.

When the twin towers collapsed, they took with them the lifeline of communications in lower Manhattan. Now, carriers are compensating for the loss and searching for the next best sites.

Quick Response

Immediately following the disaster, carriers scrambled to evaluate damages and restore communications channels with temporary sites.

Verizon was the hardest hit. Its landline central office (CO) was inside the WTC. When the CO was destroyed, most wireless carriers lost the use of their base stations and sites in lower Manhattan.

Winstar Communications helped Verizon continue service by setting up work-arounds for its customers, said William Rouhana, Winstar chairman & CEO.

Verizon Wireless lost the use of 10 of its cell sites and one microcell site. It compensated by bringing in 21 cell sites on wheels (COWs).

“We put in temporary sites at Ground Zero,” said Kevin Marchesani, Verizon Wireless senior engineer, “and surrounded the area-devastated landline.”

Nextel also was affected.

“We definitely had a good number of sites that were impacted,” said Audrey Schaefer, Nextel spokesperson. “They went out for different reasons, mostly because they were linked in on the (Verizon) T1 side.”

Nextel used a variety of resources to restore coverage. It brought in COWs, added channels to working sites, repositioned antennas and used spread-spectrum microwave communication sites.

Schaefer said Nextel also was concerned about its sites adjacent to the center. Those damaged buildings may be imploded as part of the rebuild effort. Nextel is working to find alternative placement for those sites.

Cingular also lost use of base stations when the Verizon lines went down, but no sites were destroyed, said Peter Nilsson, Cingular spokesperson. Four Sprint PCS sites were damaged in areas adjacent to the WTC, but the carrier had no sites inside the center, said Robin Carlson, Sprint PCS spokesperson.

Carlson said other Sprint sites were down because of power loss, water damage and the loss of landlines.

These temporary efforts maintained coverage. But, as rescue turned to recovery and communications returned to day-to-day interactions, wireless companies began to think about permanent rather than temporary solutions.

Second Best

The main problem carriers face with the loss of their trade-center sites is that they no longer have the premium height or line of sight. The next tallest building in Manhattan is the Empire State Building, but it presents a host of problems for carriers looking to relocate there.

“In an area like Manhattan, … you're always looking for the highest point,” said Carleton Smith, Harris Microwave Communications Division vice president of sales and marketing. “The Empire State Building is difficult because it's very small (on top).”

Antenna space on the Empire State Building is at a premium. Those who want to relocate there will have to get in line.

Pinnacle Towers, which managed the rooftop sites at the WTC, has been trying to relocate clients.

“We have been able to accommodate some of them at the Empire State Building, but we have had to accommodate other customers at other locations,” said Ben Gaboury, Pinnacle Towers president.

Gaboury said those that relocated to the Empire State Building wouldn't see much of a change in their networks compared to their lost trade-center sites.

“Their needs are most likely going to be satisfied for the long term because the coverage off both of those sites is fairly similar,” he said.

Others won't be so lucky.

“Some of the other customers that had to move to a shorter location, their coverage may be somewhat diminished,” Gaboury said. “Their alternative is going to be adding another site to supplement the coverage they've lost.”

Tim Peterson, AAT Communications vice president of sales and operations, said there weren't many options for carriers looking to relocate to other rooftops. His company manages Manhattan roofs, including the 600-foot CitiCorp building.

“There are moratoriums in Manhattan as far as tower builds,” he said. “So, as a result, we can only provide them with what we have.”

Gaboury said other New York buildings should be able to take in any new sites, but those locations will be shorter, some reaching only 200 feet.

“It's quite feasible that a customer's antenna height is going to be significantly lower as they reach down into Long Island,” Gaboury said. “Before, one site — the World Trade Center — could have handled that need. Their signal now, from their new location in Manhattan, may not travel as far. They many have to locate another station out in Long Island in order to provide the supplemental coverage.”

Depending on their network needs, some carriers only may have to add a single repeater to maintain coverage. Others may need to put in a variety of new equipment.

“You're going to start to see more of a handoff,” Peterson said. “As opposed to the towers covering 45 miles, you'll have to hand off to a neighboring site of a less-desired height.”

Peterson said wireless companies were batting around many ideas to compensate for the loss.

“There's been some talk of having satellite balloons flown up to create that height and coverage,” he said.

Although the balloons seem like an interesting idea, Peterson said the wireless community still is evaluating their cost and RF performance. Some carriers may have no choice but to redesign their RF architecture to accommodate different height levels.

To help carriers get back on their feet, Peterson said the rooftop-management companies are working together to get everyone relocated to the best possible sites.

One company, Riser Management Systems, has created a catalog of Manhattan-area buildings that would work as relocation sites. It's available at www.riser.com. Companies also have helped out by freezing rooftop rents at their Sept. 10 rates to prevent price gouging.

An Upside

Because clearing the 60-foot pile of rubble could take up to a year, most wireless companies are looking at their temporary sites as more long-term solutions than not. But, as life returns to normal in New York and talk turns to rebuilding, carriers must consider their new networks.

“If there's an upside to this whole thing, it's in the rebuild,” said Frank Del Col, TrinTel COO. “Now (carriers) can come together and develop a long-term solution for that part of New York.”

Winstar's Rouhana said the disaster provided a look into how the communications world has put all of its eggs into one basket. As we go forward, we need to protect ourselves from the consequences of these kinds of activities, he said, adding that one way to accomplish this is to make sure that there is diversity in ingress and egress from buildings.

ADC's Stroncek and Harris Microwave's Smith agreed.

“You'll see more people putting in microwave as, if not a secondary, at least a backup path,” Smith said.

Stroncek said non-fiber solutions would offer carriers more choices in case of an emergency.

“Long term, it will become critical to have the flexibility to haul RF signals over the air on an optical link rather than banking on somebody's copper cable buried in the ground,” he said.

Del Col said carriers should view the ruins as a chance to build the perfect next-generation network.

“Even though everything about this is a tragedy,” he said, “here's an opportunity to make it bigger, better and provide the redundancy and security you need going forward.”