3GSM: Ericsson to start LTE interoperability work

BARCELONA--Ericsson said it will begin interoperability testing with other vendors on its Long Term Evolution radio technology next quarter and plans to have equipment deployed with its first carrier customer by the first quarter of 2009.

In an interview at the 3GSM World Congress, Ericsson vice president of systems management Håkan Djuphammar said the physical layers for the LTE standard have been finalized, allowing Ericsson and other vendors to begin testing the basic radio interfaces of their equipment. While the LTE’s guiding body has not set in stone the specifications standards for the software layer, which include specifications for functions like mobility and security, those final puzzle pieces should be in place by September, giving vendors the full roadmap to developing LTE equipment.

LTE, alternately defined as 3.9G or 4G technology, is the latest iteration of the global cellular path beginning with GSM and deployed today as UMTS and high-speed downlink packet access (HSDPA) networks. Like UMTS, LTE will be a complete departure from its predecessor, utilizing a new radio air interface technology--orthogonal frequency division multiplexing (OFDM) instead of wideband CDMA—and requiring entirely new networks. Just as UMTS added far greater call capacity and bandwidth to cellular network over GSM/EDGE technologies, LTE is being positioned as an evolutionary leap forward in wireless architectures. But Djuphammer said LTE won’t have the same impact on the industry as UMTS. Instead, he claimed LTE would be used as a supplementary technology for carriers to expand into new spectrum and a means to replace their aging GSM infrastructure.

LTE’s theoretical capacity ceiling is set at 100 Mb/s, making it far faster than any mobile broadband technology today, but those calculations assume a broad 20 MHz channel. UMTS/HSDPA networks will eventually support 14.4 Mb/s over 5 MHz channels, meaning it would support a theoretical ceiling of about 60 MB/s when spread over the same 20 MHz. When real-world data rates are taken into account the capacity advantages are not that much different, Djuphammer said.

“If you’re looking for spectral efficiency, LTE doesn’t have an advantage over HSDPA,” Djuphammer said. “The difference between them isn’t spectral efficiency but rather LTE’s greater flexibility.”

While WCMDA technologies must fit rigidly into 5 MHz paired channels using frequency division duplexing (FDD), LTE supports time division duplexing (TDD) as well as FDD and can be scaled to fit any channel width. LTE can be targeted at carriers with odd-sized spectrum chunks and whittled down to the 1.25 MHz channels currently used by CDMA carriers. Furthermore, the 3GPP is taking measures to reduce the growing complexity of maintaining a wireless network in the new standard, adding specifications for self-configuration and self-tuning.

That makes the technology ideal for new deployments in spectrum that hasn’t been designated for UMTS and for carriers that want to gradually replace their GSM networks with a more efficient technology, Djuphammer said.