Options in Co-Location

Do you need more siting choices? Besides co-locating with other wireless providers, you should look for options in other industries. Public utilities, AM and FM radio, and TV stations all offer viable site-sharing solutions.

Carriers have avoided these options because they are not as easy as co-locating with similar service providers.

"Other wireless providers are aware of the same issues that we're concerned about, and from that standpoint, it (is) easier to work with them," said Ed Hanson, Alltel director of RF engineering.

Co-locating on alternative towers may be challenging but not impossible, he said. Alltel is starting to share sites with different technologies more now than in the past. According to Hanson, coverage needs are driving this change. Thousands of untapped AM, FM, TV and public utility towers are available where wireless coverage and capacity are needed most.

With traditional tower space in short supply, it makes sense to consider these co-location alternatives. After all, co-locating on alternative towers is certainly less expensive and complicated than building your own tower and going through the zoning process.

However, each option has its own benefits and challenges.

AM Challenges

AM stations are the most under used potential co-location partners. Mike Britner, Lawrence Behr Associates vice president of business development, estimated that there are 5,000 to 6,000 AM stations nationwide, each with up to 13 towers in key areas that wireless providers could share.

Although many regulations govern locating near an AM tower, the FCC is not overly restrictive about co-location on AM towers. Britner said FCC rules are minimal, and the process usually consists of merely completing one registration form. In some situations, interference from your equipment may change the AM pattern when you co-locate. In that case, you'll need to report the change to the FCC and pay to correct the problem.

But carriers see more formidable challenges. Joe Walsh, Omnipoint director of site acquisition, said he avoids AM towers because engineering challenges make co-location too difficult.

Alltel also tries to steer clear of AM structures for the same reason. The problem is that the entire AM tower is an antenna, and the radiating elements are on top, Hanson said. It's hard to install your equipment because the entire tower is hot, and you have to detune it so you won't distort the AM signal. You just can't throw equipment up and ground it because you'll short out the AM antenna and your equipment.

Antar Salahuddin, a former Unisite RF engineer, said most providers won't go through the complicated, expensive detuning headache of co-locating with an AM tower unless they really need the POPs in that area.

If you do need coverage in a specific area, your only option may be to co-locate with an AM tower. If so, there are ways to work around AM's engineering challenges. For example, installation and maintenance can be tricky because AM towers are hot during operation. But you can plan around this limitation. If you know that an AM tower operates only at night, you can schedule daytime construction and maintenance. Although you don't need to shut down AM towers for equipment installation or maintenance, working on the tower at off-peak hours is safer.

When planning for grounding and construction, you will need to take special precautions to protect the tower's copper-wire ground network integrity and preserve its signal. You should consider whether the AM antenna system is a single, non-directional tower or a directional, multitower array. For non-directional towers, use the tower's direct grounding to mount and bond wireless antennas and transmission lines directly onto the structure. Directional stations use multiple towers to form an FCC-licensed radiation pattern to protect other stations from interference.

Hanson said preventing interference depends on the power levels co-locating parties use.

"Sometimes we need special equipment, but not as a general practice," Hanson said.

"It depends on what the other service is and how close its frequencies are to our frequency bands."

If the frequencies are too close, filtering equipment or other solutions can prevent interference.

Other solutions include Lawrence Behr Associates' CoLoSite technology, which grounds the tower and radiates the station's signal from a modified folded unitower. Technologies such as CoLoSite use specially designed isolation coils between base-station equipment and transmission lines to prevent interference.

FM & TV Alternatives

Although there are ways around AM's challenges, there also are more attractive site-sharing alternatives available. Co-locating on FM and cable towers is much easier than sharing AM towers because the engineering requirements are the same as co-locating with wireless carriers.

"The FM towers themselves are usually just support mechanisms for the FM antennas," Alltel's Hanson said. "That's what we're looking for -- support for our antennas, rather than the tower itself being part of the radiation system; it makes it easier."

According to Salahuddin, co-locating with TV towers also is easy because the bands are far apart, preventing interference problems.

Although experienced carriers prefer these options over AM stations, they aren't without their own obstacles. For example, Alltel co-locates with cable TV when necessary, but Hanson noted that with cable, you have to consider microwave frequencies.

"We always coordinate all of our microwave paths with all of the proper agencies to ensure that interference issues are either addressed or avoided," he said. "It's part of our selection process for a site if we're employing microwave."

It also may be more difficult to work out a lease with broadcast companies. According to Salahuddin, they usually aren't eager to share their towers with wireless tenants because, despite the revenue, they find co-location a bigger hassle than it's worth. In addition, when digital TV begins to roll out in force, carriers may be booted off TV towers because broadcasters will need to add a heavier second antenna.

The Best Co-Location Option?

Omnipoint opts for sharing public utility towers over AM, FM or cable structures, Walsh said. Typically, police and fire emergency communications towers are considered essential services, so their towers are exempt from zoning height limits. Therefore, they are ideal for co-locating PCS equipment.

According to Salahuddin, PrimeCo puts its antennas on top of PU Electric's towers in Texas.

The main concern is EMF interference from 400kV telephone lines. Most EMF interference occurs in the AMPS band, and few filters are strong enough to protect against the magnetic field. This isn't an issue for PCS bands; PCS frequencies don't raise the noise floor significantly enough to create interference.

Another potential problem for analog providers is the size of their equipment. PCS equipment is small, but analog boxes can be as large as 12 feet by 20 feet, and they require a big portion of ground space that can be hard to get when co-locating with utilities.

Walsh said public utilities' structures are more desirable for PCS carriers because they don't need special equipment, and they don't have to adapt existing technology. Also, the towers usually are located in areas where carriers probably would find acquiring a site too difficult.

>From a PCS provider's viewpoint, Walsh said sharing public utility towers >is a relatively easy approach because of technology, but also because of >business issues.

"Most of the utilities, because of degregulation, are pursuing other income streams," he said.

Look Before You Co-Locate

Before you co-locate on any type of tower, evaluate site factors such as access and construction convenience, and structural suitability. You also should analyze the site for potential interference problems including intermodulation and harmonics, noise, desensitization, antenna coupling, and equipment characteristics. A sophisticated analysis technique can help you determine the vertical spacing among antenna arrays and how close your antennas can be to AM or to other antennas. The analysis also will give you an idea of the required investment.

According to Salahuddin, a computer-generated analysis that accounts for all of the site's electrical characteristics is imperative before you decide to co-locate. It will give you a good reading of the site's power level and tell you exactly how close you can be without interference.

For example, with some technologies, Salahuddin said your antennas can be five inches apart from the alternative provider's equipment, and they won't affect each other. But in some cases, your equipment may need to be installed 30 feet away from everything else.

Coping With Co-Location

In some instances, co-locating with another industry is your only option, no matter how many headaches it may cause.

You need coverage, and often local municipalities demand carriers use existing structures whenever possible.

"You're going to co-locate on any tower space you can get, regardless of who's there, and you need to do everything you can to make it work," Salahuddin said.

Hanson said co-locating in some not-so-preferred situations will continue to be an option for Alltel because its subscribers always will demand good coverage and adequate capacity. Because most carriers have the same goals in their communities, you must explore other co-location solutions.

"There are challenges, but there are remedies as well," Hanson explained. "You have to do a balancing act between how important is it to establish coverage or capacity in that area against the issues that you have to overcome and the cost of overcoming those issues."

Desirable Locations: Historically, AM towers are located in highly urbanized areas, where fill-in facilities are most necessary.

Minimal Delays: Usually, AM co-location requires little or no zoning action. Where zoning approval is needed, AM owners are influential allies, and local communities accommodate their requests. Wireless antennas mounted on AM towers are unobtrusive and are installed where residents already are used to towers.

Good Partners: Most AM station owners support co-location because it improves their facilities at little or no cost. It also generates a new, secure revenue stream.

Economical Alternative: It often costs far less to implement AM co-location than it does to build a new site. Even with structural augmentation, costs may be below a new site of comparable capacity. In addition, you can negotiate site rents favorably. Long-term costs are not significantly different from other co-location situations.

No Detuning: Network designs increasingly place site requirements close to AM stations, triggering a requirement to protect AM from signal interference with the new tower. This often requires detuning or other measures that increase site-development costs. Wireless facilities on AM towers don't require detuning.