Growing Pains

A recent study by The Strategis Group projects world wide wireless growth to increase by nearly 500 million subscribers by 2004. Increased data traffic, falling prices and new usage habits all point to increased wireless usage. The Yankee Group forecasts that the number of wireless minutes of use in the United States will jump to 500 billion by 2003, up from 150 billion today. But cellular carriers face a major hurdle amidst the bounty: how to keep costs in check while managing network growth and adding capacity.

No city embodies a growing urban center more than Phoenix. A recent Census Bureau report revealed that Phoenix, the seventh largest city in the country, is the nation's fastest-growing big city (for cities with populations more than 500,000). Between 1990 and 1998, the urban population grew 21.3%.

One Phoenix cellular carrier, faced with a growing demand for CDMA service, needed a cost-effective way to add capacity to existing cell sites quickly. A conventional strategy for boosting capacity would be to deploy another CDMA carrier frequency. However, implementing the infrastructure to support another carrier can be a costly proposition; deploying a new carrier could cost millions, eating up the bulk of annual capital budget. Moreover, adding another carrier is not always the most efficient or cost-effective way to add capacity. In most cellular networks, a lot of capacity already is built into the system but is not used.

Uneven traffic loading and subscriber demand often strain capacity in high-traffic areas, while capacity sits idle in low-usage sectors and cells. Less than 20% of a typical CDMA network's cells are capacity-strained. These are the network's capacity-limiting cells. When you deploy another carrier frequency, the remaining cells often have plenty of wasted excess capacity. Multiple network analyses suggest that as much as 70% of available capacity is wasted per carrier frequency.

The Phoenix carrier had several cell sites that were burdened with uneven sector-traffic loading, which meant the cells' capacities were not being used efficiently. The sector with the highest traffic level was heavily loaded, while unused capacity remained trapped in lightly loaded sectors.

The carrier installed a smart antenna at one site to gain control over traffic-load leveling, which is key to using CDMA capacity more efficiently. Using the system's sector synthesis capabilities, the company implemented a custom sector configuration that balanced traffic loads more evenly across the site's three sectors. After the modification, the carrier experienced a 43% reduction in peak loading. The new sector configuration shifted traffic from the capacity-strained sector to the two sectors with excess capacity due to lighter traffic loads.

The smart antenna also reduced handoff overhead by 8%. Because excessive handoff overhead is a drain on capacity, lowering handoff overhead also clears room for more traffic. The sharper rolloff of the smart-antenna sector patterns and the corresponding decrease in the size of the softer handoff regions provided this reduction.

The combined effects of peak-load reduction and handoff-overhead reduction produced a 50% increase in CDMA capacity at the site. The carrier was able to enhance the performance of its existing cell site before turning to alternative solutions such as building an off-load site or deploying another CDMA carrier frequency.

Another bonus for the carrier: The remote, software-controlled antenna configuration will allow it to adjust the site's sector configuration in real time, optimizing capacity as traffic patterns change. This benefit will ensure that capacity useat the cell site always is optimized.

As traffic levels grow in Phoenix, the company eventually will want to add another carrier, but with targeted deployment of smart antennas in a network's capacity-limiting cells, it will enjoy two lasting benefits. It maximizes the traffic carried per carrier frequency, and the capacity gains the smart antenna delivers will multiply with carrier frequency deployed. Assuming a 40% increase in capacity with each carrier added, this particular cell site can support as much traffic with three CDMA carriers as a conventional cell site could handle with four carriers.

Many cellular carriers confine the deployment of more carrier frequencies to the urban core in order to reduce the cost of adding CDMA capacity. This strategy allows carriers to avoid purchasing additional equipment for sites in lower-traffic fringe areas. But outside the urban core, busy highway interchanges, airports, shopping malls and other high-traffic areas can stress local cell-site capacity.

No matter where your markets are, surging demand for wireless service offers substantial opportunity. As a result, you are faced with the challenge of using a fixed budget to provide sufficient capacity in order to keep pace with traffic forecast. Creative ploys by marketing departments to gain new customers can leave you scrambling to deal with huge spikes in traffic that your existing infrastructure cannot handle. But if you throw a little creativity back at them, you can add capacity to your current cell sites with few increased costs.