Impedance Matching for Compact Multiple-Input Multiple-Output (MIMO) Systems
Date Issued
2011
Date
2011
Author(s)
Tsen, Wen-Fong
Abstract
Multiple-Input Multiple-Output (MIMO) system offer very high spectral efficiency and link reliability. However, correlation of signals at different antenna element can considerably decrease the capacity of MIMO systems. Such correlation occurs particularly for compact MIMO systems, where the separation between antennas is small. This thesis focuses on the effect of mutual coupling on compact MIMO systems, and capacity improvement of compact MIMO systems by introducing matching networks between the receiving antenna array and the load termination.
In the first part, we study three performance measures, i.e. signal correlation, average receive power and capacity, of a compact MIMO system with two transmitting-two receiving antennas. We begin in identifying the assumptions needed to rigorously derive the classical form of the coupling matrix. Using the coupling matrix, we investigate the impacts of coupling on the correlations and receive power. After introducing an appropriate method for power and channel normalization, the effect of matching impedance on the capacity of MIMO systems is addressed.
In the second part, the optimal single-port impedance matching for capacity maximization of compact MIMO systems with signal coupling is derived. We begin in developing the complete framework including the mutual coupling effect using Z-parameters. By maximizing an upper bound of the ergodic capacity for a MIMO with coupling at the receivers in high SNR scheme, a set of equations is formulated to find the optimum solution when the MIMO. We also prove that input impedance matching is the optimum solution when the MIMO system operates in high SNR scenarios.
Finally, we study the impedance matching problem in the presence of signal and noise coupling of compact MIMO systems. We begin in presenting a circuit model for a noisy MIMO receiver which includes arbitrary signal and noise coupling. After obtaining the MIMO capacity with spatially correlated noise, the optimum matching circuit in high SNR regime is derived.
Subjects
Multiple-Input Multiple-Output (MIMO)
mutual coupling
impedance matching
capacity
correlation
Type
thesis
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