LTE exceeding 3GPP performance targets

LTE is beating 3GPP requirements in terms of data speeds and latency in field tests, according to fresh results reported by an industry group tasked with accelerating LTE development.

The Long Term Evolution/System Architecture Evolution (LTE/SAE) Trial Initiative (LSTI), which currently comprises 21 vendors and eight operators, was created in May 2007 to validate the technology's capability and facilitate interoperability to bring it to market faster.

Testing is currently in the proof-of-concept stage, but so far, field tests from half a dozen vendors under the LSTI program have surpassed the technical requirements outlined by the 3GPP, said Julius Robson, chairman of the LSTI Proof Of Concept Group, Nortel.

Speaking at an LTE/HSPA conference in Hong Kong Friday, Robson revealed new results indicating that LTE had achieved a peak downlink rate of 154 Mbps field in a drive test using 2x2 MIMO. Another test using a 4x4 MIMO configuration yielded downlink peak rates close to 250 Mbps.

The 3GPP's baseline requirements for LTE call for 100 Mbps for the downlink and 50 Mbps for the uplink.

Robson also said that LTE was outperforming the 3GPP's baseline requirements for spectral efficiency, which is measured by number of bits per second per Hertz, for both FDD and TDD-based LTE. The latter is significant as spectral efficiency is a better benchmark for measuring unpaired TDD spectrum, where the downlink and uplink share the same spectrum band, Robson said.

That said, Robson reminded the audience that the peak rate results were for just one user in a cell, and that peak rates would be impacted by multiple users, as well as other factors such as RF conditions - for example, the speed at which the end user is moving - and application overhead.

"Peak data rates are measured at the physical layer, so there'll be additional overhead from the applications when you actually start transmitting data," Robson explained. "It's like Wi-Fi, where they say you get 54 Mbps but in reality you get half that because of all the overhead."

The LSTI has also tested LTE against such factors and the results so far have demonstrated LTE's ability to handle differing RF conditions between users and application overhead without suffering much throughput loss, he noted.

Robson also said that LTE was meeting requirements for latency: 10 milliseconds for the air interface, 20 milliseconds end to end, and 100 milliseconds for the control plane.

Robson said future proof-of-concept tests will include handover, VoIP support and drive testing in multiple cell sites.

The LSTI hopes to complete proof-of-concept tests by the end of the year, with interoperability testing running through to the middle of next year, followed by customer trials "probably in the second half of next year and first half of 2010", Robson said.

Robson said that while everyone's pleased with the results so far, getting there has been a hard slog.

"It's very difficult to get the whole industry to work together," Robson admitted. "All the vendors are competitors, and they don't want to give anything away. So trying to report on progress is difficult without worrying what the other vendor's results are going to be and what they'll make of yours."

Nevertheless, he said that the tests show that LTE well past the vaporware stage.

"A year ago, the saying was that Wimax is real and LTE is not, but we can now say that LTE is out there in the field, there are trials, and it's real," Robson said.