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It’s Time to Prepare for CTIA’s MIMO OTA Test Plan

Today’s mobile devices use multiple antennas to deliver high data speeds for video streaming and other data-intensive applications. These Multiple-Input-Multiple-Output (MIMO) antenna systems are difficult to evaluate in the lab because multiple antennas create complex operating scenarios.  Over-The-Air (OTA) testing that accurately mimics everyday operating characteristics is needed to accurately establish the true antenna performance of MIMO-based designs. 

A MIMO OTA test plan, forthcoming from CTIA, will specify the testing requirements that laboratories must satisfy to effectively perform MIMO OTA antenna performance testing.

CTIA is expected to release version 1.0 of the test plan in mid-2015. The association is also developing documents explaining what labs must do to gain CTIA Authorized Testing Laboratory (CATL) status for CTIA MIMO OTA testing, and labs around the world are now taking steps  to become  certified CATLs.  Once the test plan is released and at least 10 labs are certified, CTIA will mandate use of the MIMO OTA test plan to evaluate MIMO performance of mobile devices.  The mandate could be in effect in just a few months after the test plan is released.

Ron Borsato, Principal Architect at Spirent Communications and Vice Chair of the CTIA’s OTA Working Group, says he expects implementation of the new test standards to move quickly once the test plan is released - “The CTIA will be working to expedite validation of the test solutions with the goal of getting a sufficient number of laboratories authorized quickly so that the first MIMO OTA test plan can be enforced for certification and device approvals.”

MIMO is Complicated: OTA Testing will Improve Device Validation

So why is MIMO Testing so challenging? Devices that use MIMO techniques are fundamentally more complex than devices that use only Single-Input-Single-Output (SISO) or transmit diversity techniques. When multiple antennas are employed, performance is influenced by the number and configuration of antennas and the antenna patterns, RF front end and the antenna placement within the mobile device among other variables. MIMO performance is also influenced by user behavior – for example, the antenna pattern and the corresponding performance of the antennas can change based on the manner in which the user holds the device while watching a high-definition video.

Traditional lab tests performed over a cabled RF connection provide valuable information on baseband performance but these conducted tests are limited in their ability to provide a complete understanding of antenna performance that is fundamental to MIMO. Understanding MIMO performance requires radiated (OTA) antenna testing in a controlled environment, without cables attached. The OTA tests are carried out in a chamber that mimics real-world phone usage by creating the appropriate RF channel conditions while isolating the device from external variables that could influence test results.

The benefits of doing OTA testing for mobile devices and for MIMO performance in particular have been benchmarked in a first-of-its kind OTA study carried out jointly by Spirent and the Signals Research Group. The study report brings to light some key performance differences that could not have otherwise been revealed purely through conducted testing.

The introduction of MIMO OTA testing does not eliminate the need for conducted tests, however; those tests are still essential and required. The results of both testing processes are used to develop more holistic and reliable understanding of device performance.

Anachoic Chamber 

CTIA’s MIMO OTA Test Plan

Anechoic chamber test environments will be required with the release of the CTIA MIMO OTA test plan version 1.0. This method exposes the device under test to radiated signals from antenna probes that are very precisely positioned within a large chamber that is designed to cancel reflections. It emulates the region around the antenna while controlling external variables that could influence performance, in addition to allowing for precise evaluation under very realistic conditions and can characterize a device’s antenna pattern depending on the orientation of the device.

In addition to requiring anechoic chambers tests, CTIA is considering the use of reverberation chamber testing in a subsequent release of the test plan. This approach uses reflections in the walls of a metal chamber to model the dynamic and spatial conditions in which MIMO antennas are used.  

These two chamber solutions, when used along with a channel emulator, can create a fundamental capability to characterize not only the data performance of mobile devices, but to execute edge of coverage use cases for another very important test area - Voice over LTE (VoLTE).  

MIMO OTA and Spirent’s Role

Spirent has been a longstanding contributor to CTIA’s certification and test plan working groups and in this capacity our experts have made significant contributions to the CTIA MIMO OTA test plan. We’ve also seen, in our own labs and in Signals Ahead studies as to how accurately MIMO OTA  tests characterize antenna performance.

Whether your lab intends to offer MIMO OTA antenna performance testing with an anechoic chamber or a reverberation chamber or both, having the required infrastructure in place will position your company and your customers to meet MIMO’s very specific testing challenges. The tests will help ensure delivery of high-performing products to market, and that’s essential in the increasingly demanding mobile device market. 

If you are working on MIMO devices, you may be hearing conflicting information about Over-the-Air (OTA) testing. Get the answers in this complimentary on-demand webinar covering everything you need to know about MIMO-OTA device testing. 

 

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