The incredible shrinking cell site >BY J. QUINLAN

Cellular service providers have long been challenged with simplifying cell site installation. Cell sites can be heavy and difficult to move and install, and they usually require a building permit because of their size.

United States Cellular Corp. has found an alternative to the big, clumsy cell sites that carriers have traditionally used. USCC is the eighth-largest cellular company in the United States, and it owns or has the right to manage 140 rapidly growing cellular markets nationwide. About 18 months ago, USCC installed the first of what it calls a "cell-in-a-box," a prefabricated cell site consisting of an entire base station packed into an outdoor cabinet-type metal enclosure.

The cell-in-a-box immediately became popular because of the speed with which it can be deployed to serve a new area or improve the quality of service in an existing macro coverage area. A total of nine have been installed to date; one is on the roof of a large building, two are on mountaintops and the rest are installed at ground level in various urban and rural settings.

Previously, USCC relied exclusively on precast concrete structures for housing its cell sites. These structures were 24 feet long, 12 feet wide and 10 feet high, and each weighed 40,000 pounds. Difficult and costly to transport from the factory to the job site, such structures could not be installed without valid building permits, heavy-duty cranes to handle them and permanent, poured-in-place concrete foundations to set them on.

By contrast, the cell-in-a-box is 10 feet long, four feet wide and six feet high. Reasonably lightweight and easy to transport, the cell site rests on a simple concrete pad and occupies a minimal amount of real estate.

Because its height does not exceed six feet, the cell-in-a-box is considered a cabinet instead of a building and does not require a building permit. It fits applications where environmental or zoning restrictions might delay or even prevent building construction.

A natural evolution The cell-in-a-box did not materialize overnight, however. It evolved more out of necessity than convenience. USCC engineers were impressed with the small size and compact packaging of the remote site equipment used for personal communication services systems. The potential benefits of a smaller cell site motivated them to get the ball rolling on a cellular telephone counterpart.

Their first step was to look at essentially re-engineering the company's large traditional site. The goal was to package smaller components in an outdoor cabinet similar to those installed by wireline telephone companies. Accustomed to the appearance of telco cabinets, the public would be less likely to oppose the appearance of a look-alike enclosure.

Although the cabinets used by wireline companies were too small, USCC learned of a prototype cell site enclosure being developed by Yuasa Telecommunications International for the needs of its South American market.

While the prototype itself did not suit USCC's needs, its basic design concept was promising. Engineers from USCC and the vendor worked together on design modifications that would enable the box to work for USCC.

The redesigned cell-in-a-box now consists of an outdoor cabinet-type enclosure that houses a power system, two air conditioning units and a complete cellular telephone base station.

A door at one end of the cabinet provides access to the air conditioners. The compact, modular, 24 VDC power supply system and its rectifiers are situated behind a similar door at the cabinet's other end. A large door on the wide face of the cabinet has a piano-type hinge at its top edge. When raised and propped up by its hydraulic cylinders, the door serves as both a rain bonnet and a means of accessing the cellular telecommunications equipment in the cabinet's midsection.

Normally outfitted, the midsection contains equipment for a microwave radio link with the mobile telephone switching office and either 16 or 32 cellular radio channels. But by using an alternate provisioning method, USCC can fit up to 48 cellular radio channels into the midsection to create a three-sector cell. To gain the additional space needed in the center of the box, USCC moves all the common equipment into the power system end of the cabinet and substitutes T-1 landline facilities for the microwave link.

The battery tray is situated beneath the center of the box and contains two strings of valve-regulated lead-acid batteries. Power-dense and space efficient, these batteries provide the system with backup power for six to eight hours during commercial power outages.

Designed for use in locations with limited space and a lack of access to the sides and rear of the batteries, the cell-in-a-box was a natural choice for this application. The low-profile design of the battery tray makes it easy to install and remove cells quickly. Additionally, slots in the cover of the battery tray promote air movement and heat dissipation.

Environmental fit One of USCC's top priorities in selecting a site for a cell-in-a-box installation is to ensure that the cost of bringing in commercial power is not prohibitive. On the rare occasions when that isn't possible, the company looks for a different means of powering the site. In one instance, USCC engineers used a solar array to power a cell-in-a-box situated atop a mountain. It does the job, but its size makes it difficult to shield from view.

Another priority involves taking practical measures to prevent cell site appearances from clashing with the surroundings. A cell-in-a-box recently installed along a roadside in Tulsa, Okla., is a good example. Equipped to function as a 48-channel, three-sector cell, it was installed to improve coverage for a section of road where a large bowl-shaped depression in the earth was causing too many calls to be dropped.

The antenna pole, which USCC had to install at the site, was manufactured by a wood product company and blends in well with the foliage around it. And the cost was much less than a standard cell site.

When a building just won't work, the cell-in-a-box is a valuable addition to USCC's toolkit. And in some cases, the cell-in-a-box is more than a tool, functioning as a full macrocell.

J. Quinlan is an Engineering Manager for United States Cellular Corp., Chicago.