The Truth on 4G

by Adam Tenbrink, Manager, Global UMTS TDD Alliance
What is 4G? And how does UMTS TDD fit in?

Is UMTS TDD a 4G technology? Don't tell the marketing department we told you this, but no. It is an advanced, high-performance 3G technology. We could claim 4G, but it wouldn't be accurate.

Ask a dozen delegates at a wireless conference what 4G is, and you'll get a dozen answers. Many companies define 4G based on a sliding scale that starts with their competitor's products at 3G and their product at 4G. But the reality isn't so subjective, nor nearly as flexible. The body that actually defines what each of the "G"s is, since 1G evolved to 2G, is the ITU (International Telecommunications Union.) Within the ITU, Working Party 8F, and the Special Study Group "IMT 2000 and Beyond" are the bodies actively debating what technologies and characteristics 4G will have. Their challenge is to choose today which are the correct pieces to solve a puzzle in 2010. They need to select the specifications, requirements, and components that will define 4G.

So far, we know that the ITU expects 4G to include MIMO and OFDM for increasing the throughput and converting multi-path from an enemy into an ally. Throughput minima have been set at 100Mbps for mobile and 1Gbps in nomadic scenarios (the difference is large, because OFDM suffers under Doppler conditions.) As an end-point for diverse wireless networks, the ITU suggests 4G be IP end-to-end, and use a layered architecture that will fuse cellular, WLAN, and PAN (Personal Area Networks).

This topic is timely because the cellular carrier's LTE (Long Term Evolution) is being mapped to the ITU's vision of 4G, as is the effort of an opposing IEEE with the 802.16m version of WiMAX, announced last week. The question, then, is which version of 4G networks will prevail- the IEEE 802.16 line or the 3GPP's LTE family tree? Certainly whichever camp manages to develop the technology first will have a big advantage, but the political cards are stacked in favor of LTE, since the deciding bodies (ITU, 3GPP, etc.) are largely dominated by telcos and legacy equipment vendors. The same carriers are also the biggest market for the eventual 4G solutions. Thus, to get them to choose the IEEE solution, WiMAX "m" needs to arrive sooner, and also be significantly better than LTE.

It's an interesting race, because despite the fact that the cards are stacked against WiMAX, there are many companies working on 802.16, and a lot of smart engineers tackling the problems. It could get interesting. Surely the performance of 802.16e will be used as a gauge on how future WiMAX versions will perform. We think that WiMAX will prove to have little or no technical advantage, and will arrive too late to displace LTE. The current results of WiBRO certainly don't dissuade us in this thought.

So back to UMTS TDD. Our technology actually already contains many of the enhancements that will take 3G UMTS ahead to LTE. UMTS TDD is much less of a diversion, and more of a stepping stone for cellular carriers who want to enhance their Wireless Broadband capabilities today, while remaining on track to 4G.

www.umtstdd.org