This paper provides an overview of ongoing research in over-the-air (OTA) testing for next-generation communication and data\r\ntransmission devices with special consideration of cognitive radio (CR). Existing state-of-the-art techniques and their merits and\r\nlimitations are discussed. We identify the requirements and issues for the OTA test in a virtual electromagnetic environment\r\n(OTAinVEE) which needs to address the more complex scenario of future networks, where interference emulation becomes a\r\nhighly challenging task. A complex interference scenario arises due to the attempt to simultaneously utilize several opportunity\r\ndimensions such as frequency, time, direction (space), and polarization, in a dynamic manner in a multiuser scenario. Although\r\nMIMO-OTA testing addresses many limitations of single antenna-conducted test systems, more dimensions and parameters to be\r\naddressed in the new scenarios imply further increase in cost and complexity. Closed-loop OTA test setups for CR evaluation are\r\ndiscussed along with an overview of other test scenarios.
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