CTIA has a well-respected device testing and certification program, with 110 certified labs around the world – of which 75 are authorized to perform its over-the-air testing for device performance. The industry group has been developing OTA test plans since 2001 for devices with single-input-single-output antennas and is in the process of adding new specs to its SISO testing as well as a long-awaited test plan for devices that rely on multiple-input-multiple-output, or MIMO, antennas.
RCR Wireless News discussed the OTA test plans with Paul Moller, distinguished member of the technical staff at Motorola; and Ron Borsato, principal architect at Spirent Communications. They are chair and co-chair, respectively, of the OTA Working Group under CTIA’s certification program. Both have acted as CTIA subject-matter experts for CTIA’s single-input-single-output OTA lab authorizations since the program began.
Here are the top six things to know about CTIA’s new OTA testing:
1. Two new test plans are in the works: one for SISO and one for MIMO. As previously mentioned, SISO testing has been required by CTIA for more than a decade. The most recent update to its Wireless Device Over-the-Air Performance Testing, version 3.5.1, has already been published but is not yet in force. Version 3.5.1 for SISO adds downlink carrier aggregation for LTE and scenarios for testing devices’ ability to interact with additional location-focused networks such as GLONASS.
2. A MIMO OTA testing standard has been a long time coming, due to a significant amount of disagreement over testing methods. The major split has been between whether to use an anechoic chamber or a reverberation chamber for OTA testing. An anechoic chamber is filled with special foam pyramids to absorb signal reflections while a direct, intended signal is provided to the device. A reverberation chamber is a metal box that allows signals to bounce off its walls, with the intent of simulating a more highly scattered radio environment. CTIA has been exploring MIMO OTA testing since 2009, according to Moller, and has been looking at both approaches.
3. CTIA took an anechoic chamber approach for its initial MIMO OTA test plan. The set-up includes a device under test surrounded by eight dual-polarized antennas. The device will be rotated in the azimuth plane, or around its vertical axis, with measurements taken every 30 degrees. The device will be assessed on the basis of whether it can achieve 70%, 90% and 95% of its maximum theoretical throughput as particular signal-to-interference ratio levels are presented.
CTIA wanted to develop a test that reflected real-world conditions under which a device would be expected to operate in MIMO mode, and ultimately, the ability to have a controlled signal-to-interference level and a set of spatially diverse signals tipped the scales in favor of anechoic, according to Moller and Borsato. With an anechoic chamber set-up, Borsato said, “we could still maintain the spatial properties of the channel model” for the device under test. “A reverberation chamber illuminates a device from all angles, essentially equally. You can maintain the other aspects such power delay profiles and signal levels and such, but you can’t really separate the signals that are being sent to the DUT based on how they’re related to each other in space.”
Borsato said that the early releases of the CTIA MIMO OTA testing would focus on anechoic chamber test scenarios, but that additional work is expected to be done that may include reverberation chamber scenarios in future releases. Those tests may focus on diversity performance or large wireless devices that would not fit in the “quiet zone” of an anechoic chamber.
4. The initial phase covers 2×2 MIMO testing in the downlink only. “This really focuses on the first level of OTA MIMO evaluation, to see how well the devices are able to separate the data streams,” Borsato said. He noted that the channel model involved is the Spatial Channel Model Extended urban macro channel because it results in a more stressful test channel with high correlation that makes it easier to see performance differences across devices (Spirent covers SCME in a white paper here). Future test versions may also include MIMO testing with head and/or hand phantoms that assess the device’s performance in relation to how a user holds it.
5. Labs are gearing up for certification now. The new MIMO OTA test plan version 1.0 is expected to receive final approval in the next few weeks. Labs that want to add CTIA MIMO OTA testing certification to their repertoire must submit plans on how they will comply with the requirements so that they can be audited by CTIA experts. Moller expects that the first certified labs may come online around the end of the year, but that most of the certifications will come in the first half of 2016. A technical material for an update to version 1.1 is expected to be approved at a committee meeting in September.
6. Carriers are likely to add their own requirements. Although some carriers globally rely primarily on CTIA’s certification testing, many – particularly in the U.S. – have carrier performance limits tailored to their networks, which must be met before they will approve a device for operation on their networks. This is likely to carry over to OTA testing as well.
