In recent years, wireless operators have invested heavily in their network infrastructure. To anyone who has been around the telecommunications industry over the past decade, this fact is no surprise. The expansion of infrastructure—particularly by adding new base stations—has been the most convenient way to meet carriers' ever-expanding capacity needs. In some ways, it also has been the most cost-effective method.

Today, more than 140,000 wireless base stations are deployed across the U.S. Collectively, they provide service to more than 147 million people. As carriers have built out their footprints, wireless users have continued to gobble up capacity. Roughly half of the U.S. population now subscribes to mobile services. Intense competition and huge bundles encourage users to make more and more use of their wireless devices. As a result, minutes of use (MOUs) have skyrocketed.

At the end of 2002, U.S. wireless customers averaged 488 monthly minutes of use per person. According to The Yankee Group, that number rose to more than 500 at the end of the first quarter of 2003. In the two years prior, the average minutes of monthly use were 397 per user in 2001 and 282 in 2000. In 2002, U.S. wireless customers used an estimated 600 billion MOUs—a staggering amount by any measure (FIG. 1).

Now, customers expect and even demand that their mobile phones have performance that is on par with landline devices. This attitude was enough to give carriers heartburn. Then, the carriers realized that greater wireless traffic has led to an associated rise in radio-frequency (RF) interference. RF interference directly contributes to a greater percentage of dropped calls, blocked calls, and origination failures. All of these outcomes negatively affect customer satisfaction.

In the past, wireless carriers would address these network strains by building base stations and bringing them online to expand their capacity. CAPEX budgets have been trimmed, however, and communities have pushed back on carriers. Site selection and approval is now more difficult and costly.

In response to these problems, many carriers are beginning to adopt a "do-more-with-less" approach. To keep up with capacity demands, they must find, test, and eventually implement cost-effective alternatives to the somewhat dated solution of building base stations. The alternatives include a mixture of hardware and technology. They range from such well-publicized, cleverly named devices as smart antennas to various iterations of amplifiers, front ends that integrate cryogenic cooling, and superconducting technology.

Although the technology advances daily, here is a laundry list of the most accepted solutions on today's market:

• Smart antennas provide a very powerful performance enhancement for networks. All forms of smart antennas provide more intelligence in the directionality of the RF energy from the antenna. In all cases, the energy is focused toward the users. This can vary from simple narrower antenna patterns to complex beam forming, which tracks individual mobile users.

  Results from published tests suggest that smart antennas can increase capacity on an individual site by as much as 8X. Yet these devices can be expensive and difficult to integrate into a network. Moreover, complex integration and subsequent re-optimization require significant expertise and resources.

• Repeaters provide local RF "points of presence." To fill RF coverage holes, these points act as a means of remote coverage or capacity away from the base station. Compared to a base station, repeaters are small and relatively inexpensive. They enhance coverage in inaccessible areas, which makes them particularly attractive for tunnels, buildings, and hilly or "shadowed" terrain. But repeaters also reduce base-station capacity—sometimes substantially due to interference effects. Moreover, added costs and siting headaches can be associated with this solution.
• High-selectivity conventional filters are passive devices. They are comprised of metal cavity or dielectric resonators, which protect against out-of-band interference. The filter's size, complexity, and rejection all vary depending upon the prospective interference environment.

  These filters are inexpensive and easy to integrate. As the selectivity requirements increase, however, receiver sensitivity degrades. When high-selectivity conventional filters are deployed, receiver sensitivity is reduced. The result is coverage shrinkage and/or a further reduction in capacity utilization.

• Tower-mounted (TMAs) or mast-head amplifiers (MHAs) consist of weatherized low-noise amplifiers (LNAs). These LNAs are placed close to the antenna on the antenna tower. The tower-mounted amplifier overcomes the losses associated with cable runs to the base station. These losses can be substantial for tall towers.

  TMAs enhance receiver sensitivity—a requirement for link balance when the uplink is the limiting link. Yet reliability and associated operational issues are associated with any tower components. Plus, any interference problems will be exacerbated when using a TMA.

• High-power, multi-carrier power amplifiers (MCPAs) amplify the transmit signal from the base station to the mobile device. By increasing power on the base-station downlink, it's possible to increase coverage. Under certain circumstances, doing so will allow for increased capacity utilization.

  Different technologies, such as TDMA, GSM, CDMA, and AMPS, can be combined onto one antenna through a single, high-power MCPA system. But high-power MCPAs are expensive. They also are hard to integrate from a regulatory and a hardware/software perspective.

• Newly existing network-optimization tools use drive test and switch data to optimize coverage patterns and capacity distribution for a network. While there is relatively little investment needed for new hardware, this solution requires detailed network analysis.