The Promise and Reality of LTE

Ed. - To warm us up for the forthcoming Telco 2.0 Exec Brainstorms on new business models (next week in London and 9-10 Dec in Orlando, Florida), Telco 2.0 is blogging from eComm this week. This is probably the best event series on strategic technology developments, and we're delighted to partner with it. Below are some highlights so far. NB: Google Wave users can follow the conference backchannel by searching "tag:eComm with:public"; presentations will be posted to the individual session waves in due course.

Spectrum and LTE: promise and reality

Telco 2.0 ally Brough Turner argues that the scarcity of radio spectrum is an illusion brought on by telcos and the limits of current receiver technology. He described experiments in measuring the actual utilisation rate of the US CMRS (Cellular Mobile Radio Systems) bands; the highest utilisation rate they were able to observe was only 13%, during a US political party convention.

Surely, then, there's plenty of room at the bottom.

The reason why we don't need to regulate the visible spectrum is that the receiver - the eye - is far more sensitive and selective than any radio device we've ever constructed; if we can improve the receivers, software-defined radios could squeeze out much more bandwidth from the existing spectrum allocations, and the mobile operators' monopoly of spectrum would be subverted.

On the other hand, there's also plenty of room at the top, in the extremely high frequency bands that are currently largely unused. A major advantage here is that it's much easier to build a MIMO device for gigahertz frequencies; the distance between the multiple antennas has to be half the wavelength. so a MIMO device for the so-called beachfront spectrum at 700MHz can't physically be a mobile device because it's got to be rather longer than a laptop.

Beyond MIMO, it's becoming possible to put multiple radios on a chip as well as multiple antennas on a radio; this opens the possibility of using beamforming.

However, Moray Ramsey of test-and-measurement specialist Agilent Technologies had a bucket of cold water to go with all that optimism; he argues, based on data from Agilent's work on LTE conformance testing, that the next-generation wireless standard has serious problems. The baseline performance of LTE Release 8 radios is turning out to be a disappointment on the test stand; especially, the OFDMA and MIMO technology is more complicated than originally thought, and rather than doubling the capacity by going from 1 antenna to 2×2 MIMO, the boost is closer to 20%.

Worse, the LTE vendors have been using the wrong benchmark for comparison; LTE has been trialled against early HSPA deployments, against which it does indeed show a substantial improvement. But very few things in the industry have advanced as quickly as HSPA once it got going; peak download speeds have increased by a factor of 10 since the end of 2005 and uplink by a factor of 15. The latest wave of HSPA kit, in fact, beats the current LTE generation soundly.

As Dean Bubley pointed out in discussions later, the number of solutions to the LTE voice problem is now up to six. And worst of all, one of a list of criteria he cited as necessary to achieve LTE implementation was that IMS would need to be deployed. We've said this before; Long Term Evolution ought to mean just that - evolution, and that means that good HSPA now beats middling LTE tomorrow.