MIMO Over-The-Air Research, Development, and Testing

Multiple-input multiple-output (MIMO) over-the-air (OTA) measurements and simulations for network and terminal performance evaluation and prediction have become very important research topics in recent years. Research into MIMO OTA for standardisation purposes has been ongoing in The Wireless Association (CTIA), the Third Generation Partnership Project (3GPP), and the European Cooperation in Science and Technology (COST) for three years. This is motivated by the urgent need to develop accurate, realistic, and cost-effective test standards for UMTS and LTE systems. Although many MIMO-capable networks are already deployed, there is pressure to finish the test standards by the end of 2012. While the first MIMO devices appeared some years ago and were commercially deployed two years ago, there are not yet any standards for testing MIMO performance OTA. The development of MIMO OTA test standards has proven to be particularly complex compared to single-input single-output (SISO) OTA, and developing a test standard is taking considerable time. Unlike SISO OTA, which was relatively straightforward and purely a function of the device, MIMO OTA is highly dependent on the interaction between the propagation characteristics of the radio channel and the receive antennas of the UE. Consequently, the existing SISO measurement techniques are unable to test the UE’s MIMO properties. Many different MIMO test methods have been proposed, which vary widely in their propagation channel characteristics, size, and cost. Many challenges remain in the areas of identifying the optimal channel models and test method(s), and it is possible that the outcome could be that more than one test methodology will be standardized. Current standards activities are concentrated on showing if the proposed test methodologies provide the same results, with the ultimate goal being to clearly differentiate good from bad MIMO devices. The aim of this special issue, guest edited by a balanced representation from across academia and industry is to provide a valuable source of information for the state of this important research area. Section 2 of this introductory paper provides an introduction to MIMO OTA standardization activities, and Section 3 describes the different test methodologies under consideration by 3GPP/CTIA. A comparison between test methodologies is made in Section 4. A summary of the papers accepted for publication in this special issue is presented in Section 5. These articles discuss important aspects of MIMO OTA testing and the latest advances of all test methodologies. The research represents the latest thinking of well-known experts in industry and academia and will undoubtedly influence future decisions on testing standardization. Some conclusions and future work are provided in Section 6.