Research On MIMO Channel Capacity And Measurement Of Dielectric Parameters In Scattering Environment

As one of the most important technologies in the field of wireless communication, MIMO system can improve the channel capacity and spectrum effectiveness exponentially without increasing the power and bandwidth. It is an essential way to exploit space resource to improve the spectrum efficiency, and will play an increasing important role in the next generation of communication.The realization of the high capacity and good system performance of the MIMO system largely depends on the channel characteristics, so it is important to establish an accurate propagation channel models. The channel models can generally be divided into three different groups, the statistical models, the site-specific models and the reference models in between. A shortcoming of the statistical models is that they do not explicitly contain the information about the physical parameters, such as antenna gain. In addition, the statistical descriptions depend on the measuring equipments, and the influences of the channel and equipments on the channel model cannot be separated.In this dissertation, a general procedure of predicting the MIMO channel models based on the electromagnetic theory and the perturbation method has been presented. A MIMO system using dipoles is simulated in free space and in the scattering environment separately with electromagnetic simulation software as well as the perturbation method and both agrees very well. The relationship between channel capacity and the antenna parameters can be used to estimate the antenna size and numbers demanded to improve the performance of the communication system.The perturbation method discussed in this dissertation can also be used to study the antenna input impedance in scattering environment. Take dipole and microstrip antenna for example, the simulation results obtained from FEKO are in good agreement with the perturbation theory, which shows the feasibility of this method.On the other hand, as a research area of electromagnetic fields, the measurement of the dielectric materials attracts many colleagues’attention. The dissertation describes a new method for the determination of the dielectric materials’ electromagnetic parameters based on the perturbation theory. A dielectric sample near an arbitrary antenna will affect the input impedance of the antenna. By measuring the input impedance of the antenna in free space (without the dielectric sample) and scattering environment (with the dielectric sample), we may easily determine the permittivity, loss tangent and the permeability of the dielectric target. For dielectric targets with high permittivity, the quasi-static approximation is introduced to determine the fields in the dielectric sample, so as to broaden the application scope of this method.A measuring system using microstrip antenna has been presented to illustrate the procedure of the proposed method. The experimental results have shown that the method is accurate and effective. Compared with other methods, the method presented has the advantage of simplicity in system configuration and measurement procedures and is a non-destructive method.