Getting LTE device design right

8/19/2010 3:31 PM EDT

Right now, several cellular network operators are hurtling towards “LTE (Long Term Evolution) launch day”. The upcoming large-scale launch of commercial non-proprietary LTE is our industry’s most ambitious initiative since the first cellular networks were launched years ago.

Designing mobile devices for LTE is very different from previous mobile design efforts, mainly due to three key factors:

1. Complexity – LTE brings major, not incremental, changes to every link in the network from the core to the mobile device.
2. Multi-technology support – Subscribers expect voice and data applications to run seamlessly as they move among networks or service areas. As a global standard, LTE drives demand for devices that simultaneously support CDMA, UMTS and, of course, LTE.
3. The popularity of data applications and the demand for faster data rates.

Multiple-In Multiple-Out (MIMO) technology will significantly impact the success of LTE. It is a “game-changer’ with the potential to multiply data rates without incurring additional spectrum costs.

But when MIMO is used, the device’s physical orientation directly affects the system’s capability. The system must quickly adjust whenever the device is moving. Over-the-air (OTA) testing of device designs ensures that the system adjusts properly and quickly enough to realize the “headline” data rates promised in LTE.

Next, what happens when a subscriber launches a data application using LTE service, then moves out of range into a region covered only by, say, CDMA? Finding out requires mobility or Inter-RAT (Inter-Radio Access Technology) testing, which involves multiple emulated radio networks working in concert to provide realistic repeatable scenarios.

Since data services are a big part of the promise of LTE, data testing must be done with realistic network conditions. This includes not only Inter-RAT, RF fading, and MIMO scenarios, but adverse-condition (e.g. overloaded network) scenarios as well. In addition to throughput testing, data testing requires “data retry” testing, which ensures that a network won’t be overrun by service-connection requests when, for example, a network-based server goes down.

LTE is one of the few large-scale technologies to be deployed before the device certification process is finalized. Because of this and because of the new pitfalls outlined above, network operators and mobile device manufacturers alike are adding whole new areas of interest to their device test plans. Base largely on lessons learned from other large-scale wireless deployments, these new test plan philosophies are here to ensure that LTE delivers on its promise.

About the author
Michael Keeley is a Director of Product Management at Spirent Communications’ wireless test equipment division. He has led various teams involved in wireless network emulation and automated systems used for testing mobile devices. Prior to joining Spirent in 2000, Mike spent over two years at Lucent Technologies. He received his BSEE and MEng from Cornell University.