Tuesday, July 13, 2010

LTE and WiMAX - What's the Difference?

Yesterday, at the Convergence Technology Center sponsored Working Connections 2010 Conference In Frisco, Texas I had some time at lunch to talk about emerging mobile technologies. With only ten minutes I had to carefully pick what I wanted to discuss and decided on bandwidth and access (Surprised?!) with a focus on the two current emerging 4G technologies - LTE and WiMAX.

Lots of questions and with the time limit (people had to get back to their workshops) I did not get a chance to answer too many. People were asking about the detail differences between LTE and WiMAX. For example, is one technology better than the other? Why would one company decide on LTE while another decides on WiMAX to deliver next generation services? You said they are very similar - what makes them different?

Here’s some quick answers:

LTE will be/is the 4G technology of choice of the larger mobile carriers like Verizon Wireless (Rolling out LTE this year) and AT&T Wireless (scheduled to start LTE rollout in 2011). These carriers already have FDD spectrum and the money to buy more spectrum. The carriers will also tell you that LTE more easily supports backward compatibility with earlier cellular technologies.

WiMAX will be/is the choice of carriers with TDD spectrum and also makes sense for for greenfield situations where backward compatibility is not needed.

LTE uses FDD spectrum and WiMAX uses TDD spectrum - what’s the difference between FDD and TDD? Here’s a quick explanation from three-g.net:

Frequency Division Duplex (FDD) and Time Division Duplex (TDD) are the two most prevalent duplexing schemes used in broadband wireless networks. TDD is the more efficient scheme, however, since it does not waste bandwidth. FDD, which historically has been used in voice-only applications, supports two-way radio communication by using two distinct radio channels. Alternatively, TDD uses a single frequency to transmit signals in both the downstream and upstream directions.

Basically, FDD (LTE) uses two channels and TDD (WiMAX) uses one channel for two-way communications.

Which technology will dominate? It looks like LTE but..... there are issues with expensive and crowded spectrum. There’s a lot more TDD spectrum available than FDD spectrum and TDD spectrum is cheaper. Wouldn’t make sense to develop a version of LTE that could use TDD spectrum? It sure would and that is what TD-LTE does - it uses TDD spectrum.

Does it work? Yes! Yesterday, Ericsson ad China Mobile demonstrated an end-to-end TD-LTE solution that achieved a single user peak downlink rate of 110Mbps. China Mobile has also announced it will launch 8 TD-LTE test networks worldwide in 2010.


The Java Punk said...

Quite a while back I remember Sprint saying they were open to switching to LTE as the need might arise. Do you see them letting WiMax die off and just transitioning to LTE or using both with dual antenna phones? or just ignoring LTE after all?

Gordon F Snyder Jr said...

Great question. Thinking Sprint will be watching the China Mobile TD-LTE trials closely and (if favorable) will have the choice whether to switch to TD-LTE or not. It would put them in an interesting position.