By Tammy Parker

As cdmaOne expands worldwide, various new approaches and innovative technologies are being deployed or examined that support or enhance the performance of base stations and other network infrastructure. Could they take the bite out of network deployment costs?

Deploying any new wireless communications network is an expensive undertaking, and extending networks into less population-dense areas requires an operator’s ongoing financial commitment. However, vendors are creating a host of new infrastructure solutions that can help cdmaOne carriers keep costs under control as they aggressively launch and further expand their networks.

These technological advances run the gamut from new base station designs to alternative network layouts that include the use of repeaters, high-capacity superconducting filters or intelligent antennas.
These technologies offer a variety of approaches to coverage, capacity and siting issues that are paramount to carriers around the world.

The need for cdmaOne base stations seems insatiable. In early September 1997, Qualcomm Inc. announced it had shipped more than 1,000 of its QCell Base station Transceiver Subsystems to cdmaOne operators in Asia, Eastern Europe, North America and Latin America. Six months earlier, the company unveiled a CDMA infrastructure chipset that includes a low-power Cell Site Modem and a Frame Interface and Router Module for base station communications. The CSM and FIRM were designed to provide power savings and cost reductions for CDMA infrastructure and test equipment manufacturers.

ENHANCEMENTS
Lucent Technologies Inc. also recently announced enhancements to its cdmaOne platform, including a five-fold increase in capacity without additional base stations, thanks to a new Enhanced Channel Unit. Hardware and software modifications are enabling up to six radio carriers, again without adding base stations.

In September 1997, Motorola Inc. unveiled a CDMA cellular base station transmission system that the company claims can support about twice the capacity of current commercial CDMA networks. The company’s SC 4840 base station marks the first use of Motorola CIG’s high-density CDMA channel card, which uses a second-generation, application-specific, integrated circuit design that promises increased capacity and enhanced system performance. Further, because the equipment is smaller, carriers can realize savings in equipment room floor space of between 30% and 50%.

The SC 4840 is being deployed first in Japan by carriers DDI and IDO. "We’re using some of the aggressive build-up plans of Japan – with respect to where they want to see our CDMA networks go – as a major driving force internally to challenge ourselves to step up to the next level of performance," says Tony Kobrinetz, Vice President and General Manager of the Advanced Products Division at Motorola’s Cellular Infrastructure Group.

The SC 4840 supports the 8 kbps EVRC (enhanced variable rate coder) vocoder as opposed to the 13-kbps vocoder being widely deployed in the United States. The Japanese carriers believe the 8 kbps EVRC "will give them the capacity of eight and the sound quality of 13," notes Kobrinetz. The SC 4840 offers a six-sector CDMA transmit and receive configuration. That combination plus 8 kbps EVRC can produce capacity gains over analog networks of 16 to 18 times, Motorola says.

The SC 4840 also implements Motorola’s EMAXX, a channel element technology for higher receive sensitivity that provides better call reception and enables handsets to work at lower transmit power, extending their battery life. Such a feature is especially important in Japan, were consumers are used to small digital cellular and Personal Handyphone handsets that operate on slim, lightweight batteries, Kobrinetz notes.

MODULAR GROWTH
Like some other leading infrastructure vendors, Motorola has its own base station amplifier. The company’s Expandable Linear Power Amplifier, or ELPA, is packaged with numerous base station products including the company’s SC 4840. The amplifier provides transmit power for multiple carriers, enabling modular growth, reduction in site size, and improved installation and maintenance. While many operators thought they could use single CDMA carriers at the onset, these operators are finding that "you need to go into multiple carriers, especially in dense markets," Kobrinetz says. "We are literally planning on over eight carriers per cell site in Japan because of the density of Japan’s subscriber population." The island nation of only 130 million people has some 30 million wireless subscribers. "This is a high-volume market and one carrier of CDMA isn’t going to last very long," adds Kobrinetz.

Independent amplifier houses are also finding success in the cdmaOne market. Sunnyvale, Calif.-based Spectrian has delivered some 350,000 power amplifiers to wireless equipment manufacturers worldwide, including nearly 17,000 cdmaOne amplifiers. The company is shipping cdmaOne amplifiers at a rate of almost 2,000 per month.

Spectrian received two contracts in October 1997 from Northern Telecom Inc. for development and delivery of Spectrian’s newest cdmaOne single-channel power amplifiers, or SCPAs. The amplifiers, which are being used in Nortel’s cellular and PCS base stations, have higher performance and increased functionality over their first-generation predecessors, Spectrian says.

Like Motorola, Spectrian anticipates an increasing need for multicarrier power amplifiers, or MCPAs. While such amplifiers are more expensive than single-carrier models – an average of $11,000 for an MCPA vs. $2,500 for a single-carrier amp – MCPAs give an operator a choice of frequency assignments that can be used as carriers are added to serve capacity.

Spectrian is marketing its MC800-18 100-watt PCS MCPA for GSM and cdmaOne networks at 1800 MHz. The system integrates a combiner, amplifier and filter, allowing the devices to carry multiple modulation schemes simultaneously. And because MCPAs reduce intermodulation distortion, base stations can accommodate more customers. MCPAs also require fewer racks than using several SCPAs, limiting the required site size.
"The products that we OEM today are all single-channel because that’s what our customers have chosen to use," notes Bill Zucker, Spectrian’s Vice President of Marketing. He adds that Spectrian has sold some MCPAs directly to operators, but none of those MCPAs have been for cdmaOne applications.

Zucker says PCS operators have been slower than their cellular counterparts to use MCPAs, in part because upbanded product models are new to the market. Further, most PCS operators so far have not had to deal with capacity crunches that require them to add RF carriers.

COVERAGE GAPS
Intriguing developments also are coming in the form of repeaters, which traditionally have been used to fill coverage gaps in areas such as tunnels, campus-type settings and shopping malls that were not suitable for additional base station sites. Now, however, there is an increasingly strong business case for the deployment of repeaters to extend service into areas – such as rural highways or suburban neighborhoods – that require coverage but not the capacity offered by a full-fledged base station. With macro base stations costing upwards of $250,000 and repeaters selling for $25,000, hybrid networks appear to offer attractive returns on investment.

In June 1997, Qualcomm announced a royalty-bearing licensing agreement with Alhambra, Calif.-based Ortel Corp. to manufacture and sell cdmaOne-based wireless repeater products. At the time, Hal Zarem, Ortel’s Wireless Communications Business Manager, noted: "Among the many benefits offered by CDMA technology are inherently high capacity and a reduction in the required number of base stations. This leads to technical and economic considerations which create a solid business case for the use of CDMA repeaters, clearly the most cost-effective network element for enhancing coverage."

Sunnyvale, Calif.-based Repeater Technologies, formerly known as Peninsula Engineering, is targeting U.S. cdmaOne PCS operators with its OA 1900C network repeater. The company notes a repeater costs up to 75% less than a base station, requires 90% less real estate for siting and provides faster time to market. "Think about deploying base stations with repeaters in your original network deployment instead of looking at repeaters as hole fill-ins after the fact," says David Bolan, Repeater Technologies’ Vice President of Marketing.

The company has developed a rural deployment model for a 16-mile stretch of highway. Using 10 cdmaOne base stations to cover the highway would cost $5.5 million in capital costs: A hybrid deployment with four base stations and 14 repeaters would cost $3.6 million. Further, repeaters would reduce recurring costs for real estate, power and T1 backhaul by nearly 40%, another saving of $1.3 million over five years of operation. "To do (a hybrid system for) all the interstate freeways in the United States – that’s 45,000 miles – we could save a carrier $900 million after five years of operation," Bolan claims.

Meanwhile, there’s hot news from vendors of superconducting filters, which may fit quite comfortably in cdmaOne networks. Cryogenically cooled superconductors, operating at about -300 degrees Fahrenheit, conduct electrical current with little or no resistance and provide a high-capacity alternative to conventional RF filters. Superconductors can let most of the desired signal through while filtering unwanted signals.
Superconducting systems, which can be tower mounted or configured for an equipment room, generally sell for between $18,000 to $39,000 per unit compared with several hundred thousand dollars for a base station. Leading filter vendors are Illinois Superconductor Inc., Superconductor Technologies Inc., Conductus Inc., and Superconducting Core Technologies Inc. with its partner Raychem Corp., which together are called SCT Raychem.

EARLY SUCCESSES
Illinois Superconductor has seen early successes, with product installed at six of the 10 largest U.S. cellular operators’ networks. Other potential customers are testing receive filters for PCS at 1.8-2.2 GHz. Edward Laves, President and CEO of Illinois Superconductor, claims his company’s SpectrumMaster and RangeMaster filters decrease dropped calls 20-40% and access failures 20-50% and boost coverage 50% due to increased gain and lowered insertion loss. Because superconducting filters can fill coverage holes, he explains, the equipment can reduce a carrier’s need for new cells.

Laves says Illinois Superconductor’s unique power handling technology allows send and receive filtering. His company’s thick film superconducting system can handle 20 watts of power, significantly more than competing thin film superconducting filters, Laves says.

For now, the superconductor companies have realized the most business in the analog Advanced Mobile Phone Service (AMPS) market. Analog cellular carriers are finding that superconducting filters can be used to fill in dead spots on rural highway networks that were designed to serve three watt mobile units but now are used by customers with six watt portables. Additional coverage provided by the filters means carriers don’t need to add base stations to close gaps. "In rural communities, there’s no business case to build out networks," notes Stephen Garrison, Product Marketing Manager at Green Bay, Wis.-based Conductus.
Steven Nurnberg, President of SCT Raychem in Golden, Colo., agrees, saying: "The rural cell site is where we’re at our best." Nurnberg claims field trials of SCT Raychem’s Reach receiver front end system, which includes the first filter and amplifier in an RF chain, have shown coverage extensions of 30% to 170%. Further, Nurnberg says his company’s clients regularly see an eight percent increase in billable minutes thanks to the eradication of dropped calls. And as customers realize that they have increased coverage, their number of call attempts and completions is likely to increase.

TRIALS
The company performed trials of its Reach system during 1995 at Qualcomm’s San Diego test bed. And SCT Raychem has been involved in a cdmaOne field trial with a non-U.S. cellular carrier since February 1997, a sign that operators hope to adapt superconducting filters’ analog coverage successes to the CDMA environment.
There are some obvious benefits for cdmaOne networks. Because CDMA loads all users on one frequency assignment, ambient RF noise from those users is spread across the carrier. Additional users on a cell create additional noise, harming cell site coverage and making the system pick out each call from among all the noise, notes Laves.

Superconducting filters can reduce this "cell breathing" effect by lowering the overall noise, Laves says, thus maintaining coverage and reducing the subscriber unit power level needed.

James Simmons Jr., Vice President of Marketing and Sales at Santa Barbara, Ca11lif.-based Superconductor Technologies, notes superconducting filters can aid carriers faced with collocating equipment with that of competitors. He said Time Division Multiple Access network equipment has been shown to affect CDMA transmissions because CDMA is by nature "a noise-limited system." Filtering out ambient noise from other operators’ networks can permit collocation and maintain CDMA coverage quality, he says. "’Interference, range and size’ is our mantra," Simmons adds.

Garrison says superconducting filters are especially good candidates for use in cellular networks as they convert from AMPS to cdmaOne in order to keep the digital signals from being dwarfed by the analog ones. He admits, however, that new cdmaOne-based PCS carriers may not see the need for such technologies at this early stage because they are just learning what interference and coverage issues they will have to grapple with in each of their markets.

The superconducting vendors are interested in signing up original equipment manufacturers to market their products. "Up to now, we have primarily sold to operators," notes Laves, but the company is making a concerted effort to market its filters on an OEM basis as well.

INNOVATIVE
Another innovative technology that could find a home in cdmaOne networks is the intelligent antenna, which was designed to improve base station capacity, coverage and call quality. In fact, one intelligent antenna vendor, Metawave Communications Corp. of Redmond, Wash., is preparing to aggressively market its Spotlight Multibeam Antenna Platform to cdmaOne operators. An AMPS-compatible version of SpotLight has been commercially available since June 1997, and a cdmaOne-compatible system is slated for release in the first-half of 1998.

The SpotLight system features an array of narrow-beam antennas plus rack-based electronic equipment housed in the cell site. The system interfaces to the base station using standard RF I/O ports. SpotLight’s omni trunking capabilities let a carrier allocate channels to those areas experiencing the greatest call congestion, using signal strength to determine the best antenna.

"Our first target market for SpotLight is those wireless operators that are migrating from AMPS to CDMA. In AMPS networks, operators can use SpotLight as a cost-effective solution for spectrum clearing," notes Marketing Manager Katherine Petersen. "In CDMA networks, SpotLight will provide operators with new, more flexible ways to optimize network performance through interference control, particularly on the forward link."
Metawave uses its own Sector Synthesis technology to provide peak loading gains so operators can delay adding new base stations or deploying another CDMA carrier. Commonly used sectorization schemes for reducing interference often limit cell site capacity by restricting the number of radio channels available to each sector. However, the Spotlight system lets operators implement interference-controlling measures (such as reduced transmit power) in 30-degree increments. "By contrast, in a conventional three-sector system, operators can control interference only in 120-degree increments," Petersen says. "Optimization is further restricted when CDMA and analog networks share the same antennas, since analog sectors have more restrictive orientation requirements.

FLEXIBLE
Spotlight lets operators control sector size, orientation, and range through a software interface either at the cell site or from a remote location such as the switch. "In this way, we’ve provided a flexible system that makes the digital transition smoother, faster and less costly," Petersen adds. Sector Synthesis also can be used for load leveling, countering capacity effects of cell breathing.

With so many new technologies from which to choose, those charged with designing, deploying and building out cdmaOne networks may find themselves a bit overwhelmed. But the fact that there are plenty of advances in base station technologies and numerous alternatives to traditional wireless system design means carriers can afford to be creative as they seek to differentiate their service offerings and provide ubiquitous coverage.