Feature Article

March 20, 2009

Putting LTE and 4G into Perspective

By Bob Emmerson
Engineers are good at inventing terms that don’t make sense in the marketplace. For example, 2.5G started out as General Packet Radio Service (GPRS), not a term that trips off the tongue.  Now we have Long Term Evolution (LTE), which is being marketed as 4G. However, LTE should really be seen as a 3.9G technology. The ITU is set to approve 4G candidate technologies by the end of 2009, and that means that 4G will come about two years later than 3GPP’s LTE project.  Thus, it’s wrong to make an automatic equation between LTE and 4G.   Moreover, 4G targets peak data rates of 100 Mbps for high mobility and 1 Gbps for low mobility may hit a commercial reality wall — the cost of implementing the higher rates will exceed the additional revenues.
 
OK. Does it matter? Carriers have been awarding big LTE contracts and announcing aggressive deployment plans and everything is being marketed under the catchy 4G banner. So why, you may ask, nit pick over a relatively minor technical disparity if service performance and prices match expectations? The reason is simple: You should always look at the fine print.
 
Peak data rates capture headlines and LTE is promising a download speed around 180 Mbps. That’s a theoretical rate for one user standing in the middle of a macrocell on a sunny day with the wind in the right direction. 3G promised the more modest figure of 2 Mbps and that couldn’t be realized, which is one reason for the relatively poor uptake of 3G data services. The average and cell edge data rates are the ones that matter.
 
This time around attention 3GPP has set targets for average spectral efficiency and call edge performance; this is important. If the market focuses on peak figures, the industry can respond by adding more bandwidth or using higher-level modulation and less coding, but this will have a negative impact on coverage. When the focus is in average performance, there is nowhere to hide.
 
These words come from an excellent paper produced by Agilent Technologies (“IMT-Advanced: 4G Wireless Takes Shape an Olympic Year”):
 
“Let’s say the average speed of metropolitan rush-hour traffic is 20 mph. Compare the difficulty of designing a car that can travel at ten times the average speed with no environmental restrictions (e.g., assume perfect roads and no traffic) versus designing an entire traffic system — not just a car — that can double the average speed during rush hour.” 
It’s clear that it’s the system that counts. 
 

Bob Emmerson is TMC's European Editor. To stay abreast of the latest news affecting the European market, check out Bob's columnist page.

Edited by Erik Linask

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