Big needs, small solutions

A new generation of base stations enables wireless operators to improve in-building wireless coverage for CDMA, TDMA or GSM networks

Wireless operators worldwide are searching for creative, cost-effective ways to meet ever-growing subscriber demands for capacity, new services and quality. In high-density urban environments, especially where growing customer counts are stretching wireless networks to their limits, operators need workable and innovative capacity ideas.

By thinking "small," some wireless operators are reaping big capacity and customer gains. In several crowded metropolitan areas, providers now deploy highly specialized equipment to deliver reliable wireless coverage in a wide range of in-building applications. By covering these small, high-density structures, which can include shopping centers, corporate campuses, airports and stadiums, wireless operators can extend their coverage, attract new customers and expand overall network capacity.

The base stations used to deliver in-building coverage now offer an array of deployment and coverage options. By reducing traffic loads on the broader network, these in-building solutions also can help wireless operators boost quality and extend the useful life of their existing network equipment, and ease the migration to third generation. And in the quest to lower prices while increasing the number of customers and subscriber usage (Figure 1), operators that offer spotty coverage in dense, high-traffic areas will lose out.

While most operators are familiar with the requirements of broad wireless coverage, the confines of a closed structure pose many unique deployment challenges. Because the architecture of every building is different, in-building systems must be designed to deliver a variety of mounting and RF antenna options. Space often is limited in these interior areas, so a good in-building base station must also offer a compact and versatile equipment footprint.

In-building base stations will, by their very nature, be installed in many locations. To make them attractive to wireless operators, they must be affordable, highly reliable, designed to operate efficiently on reduced power output and extremely easy to install, operate and maintain. To meet the complex needs of a growing wireless operator, in-building solutions may be incorporated into CDMA, TDMA or GSM networks, integrating seamlessly with the provider's broader wireless network technologies. Above all, these specialized base stations must deliver high-quality, reliable spot coverage.

High-traffic solutions for CDMA

In-building CDMA base stations can deliver flexible wireless service specifically designed for high-traffic interior applications. By using many of the same components found in standard metropolitan base stations, these in-building systems can deliver reliable performance while reducing equipment, installation and network maintenance costs.

Many in-building deployments present unique space and RF coverage challenges. To meet these installation requirements, most in-building equipment features a variety of mounting options and can be deployed quickly and easily on interior or exterior walls, on a floor or inside a service closet.

Today's most advanced systems also offer enhanced hard and soft hand off algorithms, redundant control and power components and coverage at 800 MHz or 1900 MHz or both frequencies simultaneously. Some can be deployed in one to three sectors and from one to three carriers, with 24 to more than 144 channel elements for full voice capacity.

Such in-building systems typically consist of a digital enclosure housing redundant controllers, channel elements, timing unit and power system and a radio enclosure that houses radio transmitters and receivers. To satisfy the various requirements of in-building coverage, some systems accommodate up to three radio enclosures, which can be located up to 200 meters from the primary digital enclosure.

New fiber optic in-building base stations can be deployed as far as 1 kilometer from a standard CDMA metropolitan or small cell distribution element. This extends coverage possibilities and provides several deployment options. These fiber optic stations also can be placed near the serving antenna, which cuts cable loss and heightens capacity.

Distributed antenna systems are additional in-building solutions for CDMA operators, providing coverage extensions to the conventional base station for indoor environments, subways, tunnels and hard-to-reach places. With distributed antenna systems, such solutions provide coverage at a more uniform level and significantly reduce interference, resulting in higher overall capacity. These plug-and-play devices have minimal maintenance requirements.

Operators can couple wireless office services, such as smart mobile access, four- or five-digit dialing and tiered billing for separate billed plans and rate patterns, with these base station solutions to deliver on-site applications. Because these in-building CDMA solutions are 3G-ready, they also create a smooth migration pathway to 3G wireless technology.

The answer for TDMA spot coverage

Specialized base stations can deliver low-power, spot coverage that is ideally suited for in-building applications in TDMA wireless networks. Like their CDMA counterparts, these modular systems provide the small footprint often needed for space-saving interior installations. Operators are using these in-building systems to deliver extra capacity in high-traffic areas such as multitenant office buildings and convention centers and shopping malls. They also can provide extended wireless coverage in underground structures such as parking garages.

The most advanced of these technologies use a conventional single-antenna system or a distributed antenna system to provide gap- and capacity-related coverage solutions. Many TDMA operators now use these alternatives as a low-power, in-building link to their primary cellular switch platforms.

In a typical configuration, a TDMA in-building base station consists of a Compact Simplex ICRM intelligent digital multiplexer and the base station itself, which houses up to four radios, an antenna matrix, an AC power supply and an alarm unit. Such units can be mounted on a wall, on the floor of a wiring closet or in an existing equipment rack to save space and reduce the visual impact of the installation.

To provide uniform, high-capacity, low-interference coverage, many in-building base stations feature a distributed antenna system and several RF coverage options. Most in-building base stations are available with conventional antenna systems.

These small-cell TDMA base stations also can be deployed in a hierarchical cell structure. When installed underneath larger macrocells, these smaller sites can relieve capacity in the larger network to create virtual private networks using private system identifier/residential system identifier or other system identifiers or to target corporations or other niche markets with special pricing or service plans.

GSM to the desktop

Fully integrated wireless office systems for GSM networks bring full mobility, including in-building coverage and on-campus coverage, and often provide a common feature set to the desktop.

Some GSM solutions enable the operator to combine a private GSM network with the corporate network. These small-coverage GSM systems provide:

- A private wireless office system, including customized tariff and service plans, on-site/off-site call management and secure access

- Integration with the corporate PBX, providing several end-user corporate services such as abbreviated or company-specific dialing plans, an integrated voice mail system and management of incoming and outgoing calls

- GSM network services inside a building or on a campus. Corporate users benefit from the same, near-wireline voice quality and services enjoyed by wide area GSM network users

- Tailored billing plans that allow operators to develop alternative tariffing options for on-site GSM communications. Billing options include the ability to differentiate between on-site and off-site calls, between corporate users and visiting users and so on

- A scalable platform that allows for on-demand development of a wireless office system, beginning with a small target population and growing larger and more diverse.

Such GSM wireless office solutions also support the deployment of a unified corporate voice and data network. This includes data and general packet radio services capabilities that bring advanced wireless applications into the office, including wireless e-mail, intranet access and customized applications.

The wireless office has the ability to plug into the corporate LAN via an IP interface, allowing GSM corporate data traffic to be carried over the LAN, thus eliminating the need to operate separate networks for voice and data. Using a MAP-D (mobility application protocol)-over-IP interface, all of a company's sites can be integrated into a global virtual wireless network, allowing employees to seamlessly roam from site to site and use the same wireless service set between separate units.

In-building advantages

By providing localized coverage for selected structures, wireless operators can deliver reliable, cost-effective service when and where they need it most. Strategically placed in-building base stations can measurably increase the overall traffic capacity of most wireless communications networks.

Today's in-building solutions can reduce site acquisition, installation and maintenance expenses for wireless operators, allowing them to put coverage when and where they need it without purchasing excess cell site capacity. Operators can use in-building base stations to extend airtime usage patterns or to target corporate or institutional subscriber prospects with tailored services. In-building technologies also lay the groundwork for a smooth migration to 3G wireless networks.

When capacity limitations strain the efficiency of their networks, wireless operators now can use in-building solutions to boost coverage and productivity. For any growing network, these small-space solutions can deliver some very big performance results.