MIMO terminals performance evaluation in a local propagation context

Multiple Input-Multiple Output (MIMO) is a technology of growing importance in present and upcoming wireless network standards (WIFI, 4G, 5G), as it is anticipated to provide large performance gains, mainly in terms of link/network capacity and link robustness (through diversity). However there is no free lunch and implementing MIMO is neither simple nor always beneficial. Among the several problems encountered is the fact that the operating conditions of MIMO terminals are, often, far from ideal and subject to a set of impairments. In particular, the antenna signals are not uncorrelated and not identically distributed, as often considered in historical and simplistic MIMO system models. What´s worse is that these impairments are not uniquely defined for a given terminal but they critically depend on the electromagnetic environmental conditions, both regarding the immediate vicinity of the device (user body, supporting hardware...) and the farther distant local propagation context (indoor, outdoor... environment). In other words, many sources of joint antenna-channel impairments do affect the MIMO terminal performance, which should be identified and modeled for an educated understanding and an accurate performance evaluation and optimization of wireless networks.