For wireless communications systems, user device testing was originally based on conducted measurements. Even on component level, RF connectors were available for measuring metrics and characterizing RF performance. Such metrics can be divided into TX performance parameters such as power level, EVM quality or spectral emissions, and RX performance parameters such as receiver sensitivity and selectivity. Antenna implementation also plays a crucial role in overall performance.
Due to the increasing integration of chipsets and antennas and the use of higher frequencies in the millimeterwave range, the boundaries between chipset testing, RF testing and antenna characterization have become blurred. Highly integrated antennas no longer allow isolated testing of chipset and passive antenna components. In FR2, cable connectors are no longer feasible. Aspects like shrinking component sizes only produce minor effects. In contrast, there are major challenges related to costs and other problems such as path attenuation, RF matching between connectors and susceptibility of connected setups to bending. The main impetus for a paradigm change in the test setup was the introduction of directional antennas in UEs. As a result, beamforming is no longer a feature that is only found in base stations. A new measurement domain was created.
Analogous to familiar time-based metrics (e.g. power versus time), spectrum-based metrics (e.g. spectrum emission mask) and code domain-based metrics (e.g. code domain power), spatial domain-based metrics are now important. Terms like spherical radiation pattern and spherical receiver characteristics have become commonplace in the T&M industry. Measurement characteristics and requirements specified by standardization organizations like 3GPP have been updated accordingly. Conformance testing must ensure proper implementation and operation of applicable systems.
The objective of this paper is to discuss the technical background for over-the-air (OTA) testing. Focusing on UEs, the paper examines the requirements described in the technical specifications.
