Filters for the future, Superconducting technology heats up >BY JASON MEYERS, Wireless Networks Editor

In the hyperkinetic, do-or-die world of wireless, network operators focus first and foremost on getting their systems in place and turned on. As they level off, however, they are beginning to look at alternatives for tweaking and enhancing their networks.

Superconducting filter technology is one alternative that is beginning to turn more heads in both cellular and personal communication services circles. With the backing of a handful of small vendors, the alternative to conventional RF filtering is on its way to becoming an important peripheral component of wireless systems.

Superconducting filters are composed of materials that exhibit high resistance to undesirable signals when cooled to very low temperatures. Proponents of the technology say the benefits-reduced interference from out-of-band sources, increased capacity, enhanced antenna range-vary depending on the operating environment and the design of the network system.

Cellcom, a cellular carrier operating in rural Wisconsin and Iowa, is testing the ClearSite receiver subsystem from Conductus to gauge its effectiveness for range extension.

"The rural operating companies are most concerned about coverage," said Duncan McMillan, vice president of marketing for Conductus. "They tend to put up very large towers, and they want the maximum range because the regions are so sparsely populated.

Other rural carriers are thinking along those same lines. Alltel Mobile is currently conducting a trial of the SpectrumMaster Filter from Illinois Superconducter at a code division multiple access site in Little Rock, Ark.

But developers of the technology are not ruling out urban cellular operators and PCS providers with footprints in both types of regions. American Personal Communications, for one, tested the Reach receiver front end from Superconducting Core Technologies last year in its PCS network.

"For urban cellular operators, capacity and interference reduction considerations are the most important," said Charles Shalvoy, president and chief executive officer of Conductus.

Ora Smith, president and CEO of Illinois Superconducter, said that in addition to extending range in rural systems, his company's equipment has proved beneficial in airport environments, busy urban cell sites and "antenna farms," where many operators have co-located their equipment. "In systems operating in high-interference environments, we improve system operation significantly," Smith said.

In trials, SpectrumMaster helped to decrease dropped call rates by up to 50% and to increase range by up to 25%. Decreases in noise reduction and subscriber power levels were also noted.

"The cellular retrofit business is a good fit for this product," he said. "Those operators have more of an incentive to improve their systems.

Superconducting Core Technologies is targeting both types of operators but taking a slightly different tack, said Ron Olexa, SCT's chief operations officer. "We determined that the way to get the optimum benefit is to get the filter as close to the antenna as possible in order to minimize line loss." One of the benefits Olexa has noted in trials of SCT's equipment is an improvement in the signal from the subscriber back to the antenna, which alleviates a common problem in existing networks.

"Every system I have seen seems to be uplink limited-they can talk further than they can hear," he said.

All three vendors have struck development or distribution deals with larger entities in efforts to gain more backing and exposure for their systems. Both Conductus and Illinois Superconducter have co-development agreements with Lucent Technologies, while SCT has a formed an alliance with Raychem Corp. for distribution and has tested its products with both Nokia and Qualcomm.

Curiosity levels about superconducting filter technology appear to be rising in the carrier community, with some hurdles yet to be surmounted. McMillan of Conductus said the fact that the filters have to be kept cold is sometimes a sticking point. "But everyone we've talked to has been pleased that the refrigeration part is very much transportable," he said.

"Carriers are initially skeptical, and once they get operational experience with it they tend to be cautiously accepting," said Smith of Illinois Superconducter.

Still, the fact that none of the players in this technology area has yet been granted a sizable contract indicates that wireless operators have not yet seized upon superconducting filters as the next big thing. "No one has made the mass market yet," said Conductus' Shalvoy.

AERIAL BEGINS FLIGHT TEST Aerial Communications has begun a 400-user trial on its new personal communication services system in Columbus, Ohio. Potential business and residential customers were selected by Aerial to participate. CDMA SPREADS NORTHWEST AirTouch Cellular is now offering its Powerband code division multiple access service to customers in the Puget Sound region. The network, equipped with 13 kb/s vocoders, stretches from the Canadian border to Olympia, Wash., and from the Cascade mountain range to the Olympic Peninsula. ERICSSON BROADENS FOOTPRINT Radiomovil of Mexico has granted Ericsson a $495 million contract for an IS-136 digital AMPS system that includes a wireless intelligent network platform. Ericsson has also received a GSM order from Eurotel of Slovakia.