Nextel is taking another crack at finding a suitable technology for its 2.5 GHz spectrum, announcing today it would deploy IPWireless’ time division-CDMA (TD-CDMA) technology over those airwaves in a limited trial in Washington.

The news is significant for IPWireless, which has so far seen interest in its technology in Europe. Last week, IPWireless announced its first commercial deployment with a Tier 1 carrier, T-Mobile, which is rolling out TD-CDMA in the 1.9 GHz and 872 MHz bands throughout the Czech Republic.

Nextel will turn the service up in the third quarter, installing the radio gear on towers in Washington, D.C.; Arlington and Reston, Va.; and Bethesda, Md. While the footprint of the network will be large, Nextel is only extending the trial to between 300 and 400 existing Nextel cellular customers. The limited scope of the trial is in contrast with the commercial pilot of 3G technology launched last year in Raleigh, N.C., using Flarion’s Flash-OFDM gear. Nextel discontinued the trial earlier this year, saying it would evaluate the pilot’s results. A Nextel spokesman today said the carrier has been evaluating several technologies in its labs, including Flash-OFDM and TD-CDMA, as possible high-speed data technologies. And like Flarion’s gear, IP Wireless’ equipment will get a similar evaluation period, though this one may be as short as six months, he said.

“We’re investigating all viable technologies,” the spokesman said. “We’ve been testing [IPWireless’] technology in lab environment, and now we want to see how it operates in real-world conditions.”

Nextel has been searching for an answer to the other Tier 1 operators’ UMTS and CDMA 1X EV-DO networks. Unlike the other major carriers, Nextel’s networks use a proprietary radio technology developed by Motorola called iDEN, which does not have a 3G migration path. The planned merger of Sprint and Nextel, however, was thought to have put an end to that search since Sprint has clearly chosen EV-DO and its future revisions for its 3G migration. But Nextel still appears to be actively looking for its own 3G equivalent. The spokesman said that the Nextel is continuing on its normal business path until the merger is finalized, and even then the combined carrier will continue to run separate networks.

While Nextel’s TD-CDMA trial is unique in the U.S., the technology’s traction with European carriers is no coincidence. TD-CDMA is part of the UMTS standard, and in Europe regulators handed out TD-CDMA UMTS licenses as well as spectrum for the much more common wideband CDMA (W-CDMA). TD-CDMA is a time division duplexing (TDD) technology, delivering the uplink and the downlink on a single channel at alternating periods, while W-CDMA uses frequency division duplexing, using paired channels to transmit the uplink on downlink on different frequencies. Because W-CDMA technologies were developed first and more spectrum was available at its designated bands, carriers naturally deployed W-CDMA first, leaving their TD-CDMA spectrum un-used. But carriers have begun expressing more interest in using that spectrum, and many have started looking to IPWireless. In addition to T-Mobile, Orange has been conducting trials of TD-CDMA.

In the U.S., however, there are fewer particular technology requirements attached to the spectrum, meaning Nextel can choose to deploy TD-CDMA, Flash-OFDM or even WiMAX over the frequencies.