Characterization of Small Antennas & Wireless Devices for MIMO Systems in Rich Isotropic Multipath & Random Line-of-Sight

Licentiatavhandling, 2013

The current thesis is about over-the-air (OTA) performance characterization of wireless terminals in rich isotropic multipath (RIMP) environment as well as in pure line-of-sight (LOS) environment while not ignoring the random positions and orientations of the mobile terminals due to randomness of the user. The latest mobile wireless terminals such as iPhone and iPad can be used in any random position and orientation thereby making the received LOS-component to appear as a random voltage at the antenna ports. The terms such as "RIMP" and "Random-LOS" are coined to represent two limiting environments for OTA performance characterization of mobile terminals. The RIMP environment is emulated by reverberation chambers while pure-LOS is emulated by anechoic chambers. Mobile terminals are mostly used in multipath environments, e.g. indoor environments and therefore the focus of this thesis is about measuring and simulating diversity gains, channel capacity, and throughput of wireless devices in a RIMP environment. The papers [A-D] discuss some work related to using RIMP as a reference environment and study convergence of diversity gains and capacity. The reverberation chamber has been used to measure both passive antennas and complete active wireless devices for many years. Recently, the active measurements of Long Term Evolution (LTE) or 4G devices have become very important in order to test implemented Multiple-Input Multiple-Output (MIMO) diversity and Orthogonal Frequency Division Multiplexing (OFDM) technology. Features such as adaptable modulation scheme, system bandwidth, coding rate, and diversity have made communication system more robust and adaptable to the environment. A theory to estimate the OTA throughput of LTE devices including the diversity gains due to MIMO and OFDM is presented and tested for different LTE system bandwidths and coherence bandwidths in papers [E-H]. During the last few years, we have developed multipath environment simulation tools to study convergence, to validate measurements in RIMP, and to study other multipath environments for comparison. Most of the work in this thesis is based on these simulation tools i.e. Rayleigh-lab and ViRM-lab. A section of many listed papers discuss about these simulation tools. At Chalmers University, a multiport ultra-wideband (UWB) bow-tie antenna has been designed and developed during last few years. The OTA performance characterization of this antenna has been done by measurements and simulations in RIMP environment. The results are discussed in papers [I-J]. The OTA performance characterization of single-port mobile terminals has been studied for several years now. Today, we have LTE mobile terminals with multiport antennas which must be be characterized for OTA environments. The OTA performance characterization of a two-port mobile phone mockup on both sides of the head following standardized talk positions is presented and discussed in papers [K-L]. The OTA performance of a compact UWB antenna developed for mobile phone applications at Linkoping University is discussed in paper M. The antenna covers all important bands such as GSM, UMTS, LTE, Bluetooth, and WLAN, etc. Keywords: OTA, RIMP, Rayleigh, reverberation chamber, random LOS, LTE, MIMO.