A Smart Solution

It's been less than a year since service providers first deployed CDMA smart antennas commercially. But the benefits already are being realized. Service providers are ordering multiple smart-antenna systems to alleviate capacity constraints in major metropolitan networks. Bearing out projections and delivering on their promise, smart antennas have proved a cost-effective way to add capacity in high-usage areas.

The need for CDMA capacity solutions is evident as subscriber numbers grow and service providers try to meet digital demand. Many providers are forced to add CDMA capacity earlier than planned, accelerating the deployment schedule for costly network-wide upgrades to add carrier frequencies. Smart antennas allow you to delay these costly upgrades.

With smart antennas, you can add CDMA capacity incrementally, on a site-by-site basis, just in areas where it's needed. This flexibility, not available with carrier frequency upgrades, allows you to respond to the characteristics of individual cell sectors, which can have significantly different traffic loads. For example, often the heaviest-loaded sector in a cell has more than twice the traffic density of the least-loaded sector. Smart antennas are the only capacity solution to address the inefficiencies of uneven load balancing, a leading cause of capacity constraints in CDMA networks.

Smart antennas adjust the cell's radiation patterns to balance traffic loads across sectors. The system maximizes capacity through a phased-array antenna, which synthesizes custom antenna patterns in response to a cell's loading characteristics. Without a smart antenna, you cannot adjust sector size and orientation easily. The capacity of the most heavily loaded sector limits the entire cell's capacity, even though the more lightly loaded sectors may have capacity to spare. A smart-antenna system redistributes the traffic load by varying sector size and orientation. Smart antennas are software-controlled, allowing you to respond to traffic-level changes in real time. Because you can respond to network-demand variations, you can optimize cell-site capacity over time.

A Case Study

In one case, a service provider installed a CDMA smart-antenna system at a metropolitan cell site that provided service along several major highways. The network was experiencing rapid CDMA growth with concentrated usage areas. The smart antenna leveled traffic loading, reduced overhead handoff and increased the site's capacity nearly 30%.

In the first phase of smart-antenna deployment, the service provider analyzed the coverage area to determine the cell site's performance before it installed the smart antenna. The cell's three sectors -- alpha, beta, gamma -- had significantly different traffic loading. The beta sector, which provided service for two major highways, carried a much higher load than the alpha and gamma sectors. Its average load was 140% ideal, compared to an ideal of 100% loading on all sectors.

When the smart antenna was deployed, the azimuth of each sector was rotated 60 degrees clockwise, which split the heavily loaded area between two sectors and brought all three sectors within 14% of ideal loading. Comparing statistics before and after deployment revealed the system reduced forward-power overload control (a measure of blocking duration) by more than 60% even though it carried a higher level of total cell-site traffic. The system reduced peak loading in the beta sector by approximately 20% and reduced the cell site's handoff overhead by 7%. The smart antenna cleared room for growth, allowing the site to carry more traffic and generate higher revenues.

Economic Value

In addition to solving traffic-load imbalances, smart antennas allow you to deal with uneven traffic across an entire network more effectively.

Typically, fewer than 20% of a network's cells require another CDMA carrier frequency. Unfortunately, because of guard-zone requirements and the reduced reliability of hard carrier-to-carrier handoffs, service providers deploy carriers across large areas of the network. As a result, you buy capacity for areas that don't need it.

A more economical approach is to add smart-antenna systems to the overloaded sites, then upgrade to another carrier frequency when it is required in more sites. This allows you to meet immediate capacity needs for significantly less expense, and allows you to postpone a major capital outlay.

For example, if, on average, it costs 100,000 dollars to upgrade each cell in a 100-cell network, you face a 10 million dollar upfront capital expenditure when deploying a new CDMA carrier frequency. If capacity is constrained in only 20% of the cells, as is usually the case, you are forced to pay for an upgrade in areas where capacity is not needed. In other words, 80% of the investment in new network infrastructure doesn't provide short-term benefits.

With a smart-antenna solution, you can add capacity exactly where and only where it's needed -- in this case, the 20 capacity-constrained cells. As a result, you can purchase the needed capacity for much less than adding another carrier.

By extracting more capacity from the current network resources -- both the spectrum allocated to CDMA service and the current cell-site equipment -- you can use smart antennas to postpone the costly, labor-intensive deployment of another CDMA carrier frequency.

You will notice capacity and economic benefits of smart antennas at each stage of network development (at each subsequent addition of a CDMA carrier). Smart antennas increase cell-site capacity up to 40% per CDMA carrier. Assuming a 40% capacity gain per carrier, a smart-antenna cell can carry as much traffic with three carriers as a conventional cell site can carry with four.

Smart antennas allow more efficient use of network investments and more predictable, manageable growth. You will not have to spend capital on network-wide infrastructure upgrades until there is a network-wide need. This can have a profound effect on long-term business planning.

Smart-Antenna Architecture

A smart-antenna system features a software-defined multibeam antenna array and a PC-based configuration tool. The latter provides a remotely accessible user interface that allows operators to monitor capacity characteristics in 30-degree increments around the cell and to configure antenna patterns accordingly. Using sector-synthesis technology, you can adjust sector configurations, including azimuth pointing angles and sector beamwidths, based on variations in traffic, terrain and RF conditions, or based on the time of day or day of week. A GUI allows you to model, optimize and display pre-set and custom antenna patterns.

Smart-antenna systems also include a suite of multicarrier linear power amplifiers (LPAs) that provide considerable flexibility for expanding networks. LPAs, which typically offer superior watt-per-dollar performance, replace the existing base-station power amplifiers. When you add new CDMA carrier frequencies, and power needs increase, the suite of LPAs, which features a load-sharing architecture, provides a seamless expansion path that can alleviate power constraints in power-limited cells.

Dual-Mode CDMA/Analog

Most cellular providers manage analog and digital traffic and will continue to do so for many years. Dual-mode smart-antenna systems can help ease the digital migration strategy. These systems allow you to configure different sectorization patterns for CDMA and analog operation through the same antenna structure. This provides optimal CDMA capacity and performance without affecting AMPS customers, and without the extra costs and zoning hassles associated with installing two sets of antennas.

Dual-mode smart antennas increase the capacity of AMPS networks through tighter frequency reuse and greater trunking efficiencies. Smart antennas can double analog capacity, allowing you to serve the same number of analog customers on fewer channels. This streamlines the spectrum-clearing process, makes way for new digital customers, and gives you one platform for managing AMPS/CDMA capacity and spectrum.

Evolution

Today, CDMA providers are recognizing smart antennas as an integral component of a cost-effective network growth strategy. Smart antennassoon will be compatible with all leading base-station equipment and air-interface protocols, extending their benefits across all wireless networks. Smart antennas for GSM networks are on the horizon, with the first systems expected to appear by year-end.

This trend will continue into the future. Smart antennas will play a role in 3G networks. Proposals for 3G wireless standards, IMT-2000 and CDMA-2000, include extensive support for smart antennas, proof that the industry is embracing smart-antenna technology as a key to capacity and an integral network element.

What was up at CTIA Wireless 1999? Antennas, and plenty of them. Companies highlighted some of the latest antenna technology.

* Antenna Specialists, a division of Allen Telecom, introduced a fixed-station, dual-band antenna for in-building wireless communications. The ASP-3561 omnidirectional, vertical-polarized antenna operates in 824MHz to 960MHz and 1,710MHz to 1.9GHz for digital and analog environments. The antenna is 8.1 inches in diameter and 2.5 inches deep.

* Maxrad announced its MP 19000 series of directional panel antennas for PCS applications. The PCS directional panel antennas are available in three models. MP 19008 and 19011 offer gain capabilities of 8dBi and 11dBi, with a VSWR ratio of less than 1.5:1. Model MP 19013 offers 13dBi gain with a VSWR ratio of less than or equal to 2:1.

* Andrew's Parx series of unshielded, parabolic antennas is suitable for 2GHz users that are migrating to 6GHz, 10GHz and 11GHz for PCS, cellular, site-interconnect and backhaul applications. The antennas provide high front-to-back ratios and medium- to high-capacity system capabilities.

* EMS Wireless' DualPol Omni antenna for 1,850MHz to 1.9GHz PCS frequencies was designed for micro-base-station deployments. The dual-polarized, omni-directional antenna offers a slant 45-degree polarization diversity with omnidirectional coverage. It eliminates the no-diversity zone that exists in 2-branch spatial diversity systems along the axis of the two vertical polarization omni antennas. The antenna also includes upper-sidelobe suppression in the elevation pattern, which reduces co-channel interference. It is 6.25 inches in diameter, 57 inches tall and has a 10.7dBi peak gain.

* Ball Wireless' DualBase dual-band, base-station antenna has a 1-connector, 1-cable design, reducing installation, tower costs and congestion at base-station sites. Model DVA-VR-16-09007 is designed for cellular and PCS networks. The vertically polarized antenna provides approximately 16dBi gain for PCS to help equalize coverage with the 14dBi gain in cellular. Horizontal and vertical beamwidths for PCS are 90 degrees and 7 degrees. Horizontal beamwidths for cellular are 90 degrees and 14 degrees.

* Raytheon Systems introduced its active-antenna solution for fixed and mobile applications. The advanced antenna system increases the radio base-station coverage area by incorporating phased-array antennas and active electronics, distributed power amplifiers, and low-noise amps to achieve the 1,640EIRP maximum. The active antenna technology also balances uplink and downlink performance by minimizing the effects of antenna cable losses and increasing cell site radiated output power and reliability. Raytheon's active antenna solution is part of its Maxite radio base-station solution.

Features: Software-controlled, phased-array antenna

Benefits: Customize antenna patterns to cell's traffic load and terrain; Maximize antenna investment

Features: User-configurable sector beamwidth and sector orientation

Benefits: Increase site capacity up to 40% by balancing traffic loads and reducing handoff overhead; Reduce blocking and capture more revenues per site; Increase capacity site-by-site; Delay deployment of next CDMA carrier frequencies

Features: User-configurable per-beam gain

Benefits: Sculpt cell footprints; Extend coverage for buildings, other dense locations; Limit coverage overshoot and pilot pollution; Reduce intercell handoff; increase forward link capacity

Features: Time-based sector configuration

Benefits: Adjust sectors in response to time-varying traffic loads; Provide capacity where and when needed

Features: Independent control of CDMA and analog sector patterns

Benefits: Eliminate limitations of CDMA/analog antenna sharing; Reduce antenna count; Avoid extra tower loading

Features: RF-performance statistics logging

Benefits: Fine tune optimization with new capacity data available in 30-degree increments; Assess network needs/performance; Better automate traffic leveling

Features: Remote configuration

Benefits: Configure the smart-antenna system from NOC, MTSO or engineering offices; Make on-demand changes quickly and easily; Make fewer trips to cell sites

Features: Multicarrier linear power amplifiers

Benefits: Receive superior watt-per-dollar performance; Establish economical power migration path; Alleviate power constraints in power-limited cells