14 April 2009
Testing times for LTE
It's widely acknowledged that Long Term Evolution (LTE) is the inevitable next step in radio communications and should be available commercially in 2010. That means test issues need to be addressed sooner, rather than later.
The objective – improving the universal mobile telecommunications system (UMTS) mobile phone standard – has however, created a number of challenges.
Primarily, this is because the 3GPP has yet to ratify the standard, so much of the effort will be orientated around upgrading UMTS to 4G mobile communications technology.
And there are other concerns – for example, the need for an all IP flat architecture system and the small matter of possible delays caused by the budget tightening recession.
While the format war between the competing 4G networks, LTE and WiMax continues, it looks as though the industry is backing LTE. And it's easy to see why when one considers its advantages – high throughput, low latency and simple architecture resulting on low operating expenditures. But for many the crunch factor is its ability to support seamless connection to existing networks.
Once again, this raises further challenges for test equipment manufacturers. Rohde & Schwarz' production manager, communications test, Lindsay Harris warned: "The problem with LTE is that it introduces new data rates and different throughput rates. To combat these issues we have found it necessary to collaborate with both operators and customers. It's a chicken and egg scenario as we need mobiles to test and to analyse software – while manufacturers' products need testing during the research and development phase."
At Mobile World Congress, Harris witnessed the extent of the technology's capabilities. Several demonstrations revealed mobiles showing throughputs in excess of 20Mbit/s. "These days, it's all about throughput," Harris observed. "The industry used to run protocols, now it wants to show the world what its datacard can do over the air."
Testing LTE has also raised a number of problems from an rf point of view. "We now have new modulation schemes." Harris noted, "not to mention new protocols. Whereas, we've previously seen an evolution of existing standards, LTE is totally new, so we've had to approach it with the view that it has totally new technology and protocol architectures."
WiMax, too, has emerged as a global force to be reckoned with. Harris continued: "We've seen WiMax become hugely successful in many parts of the world, but different players have had to make a decision between standards. Despite WiMax' success – and the fact that it has more applications - most have chosen to go with LTE. This may be because WiMax is not a natural evolution of 3G standards."
So how has Rohde & Schwarz addressed the challenges of this new standard – with data rates up to 150Mbit/s and low latency?
Harris said: "The enormous increase in data rates compare with UMTS and the significant pressure for a quick market launch have been driving factors in the current development of LTE mobile radio devices. As a result, the complex functioning and performance of the higher protocol layers of user equipment must be verified very early in the development process."
Rohde & Schwarz developed its CMW500 range by working closely with numerous standards bodies. The primary challenge, according to Harris, was attempting to meet specifications that had not yet been implemented. "For us to test our products, we rely heavily on close cooperation with standards bodies to cover every possible angle." The result of such collaborations was that the company's test range was adaptable enough to suit protocol, rf and production needs – or, as Harris described it, 'a box for all requirements'.
Author
Chris Shaw
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