Characterization of the Spatial Distribution of the Electric Field Strength in Indoor Propagation at 2.45 GHz

Small-scale spatial variations of the electric field strength or “fast fading” are encountered in indoor environments, and are of particular concern for indoor wireless communication applications as well as for electromagnetic compatibility assessment. This thesis is motivated by the problem of electromagnetic interference with a critical-care medical equipment caused by fields radiated by portable electronic devices such as cell phones and tablet computers. Measurement and computer simulation of the electric field strength, in both controlled and real-world scenarios, are explored to estimate parameter values of statistical models for the fast fading in a region of interest inside a building. First, a method for measuring the dielectric constant of wall construction materials is developed for two reasons: little information available on electrical properties of such materials in the frequency range of interest, 2.4 GHz ISM band, and variations in material properties caused by different manufacturing processes employed by different manufacturers. The proposed technique, referred to as the parallel-path method, falls into the category of free-space methods and is shown to be more sensitive to the dielectric constant than free-space methods based on normal incidence only. Having determined the dielectric constant of gyproc slabs and of a wooden door, a controlled multipath environment is built inside an anechoic chamber. Two line-of-sight and a non-line-of-sight scenarios, each with about 4000 measurement points, are studied. We apply the Friedman’s goodness-of-fit test at 5% significance level to show that a ray-tracing technique based only on 3D geometrical optics is suitable for estimating the fast fading of the electromagnetic field at 2.45 GHz in a very controlled situation. Then the Anderson-Darling goodness-of-fit test, also at 5% significance level, is applied to show that in the vicinity of a transmitter the Ricean, Normal, Nakagami, and Weibull distributions can be equivalently used to represent the spatial fast fading for both line and non-line-of-sight scenarios. Furthermore, the effects of metal studs are shown to worsen not only point-by-point agreement between measurement and GO simulation, but also the agreement on the statistics of the fast fading in a 65 by 65 cm region. Another aspect of this thesis is the development of a new method for estimating the parameters of the Ricean probability density function. This new method is compared to the maximum-likelihood method, and is shown to provide accurate estimates with samples containing as few as 36 data points for regions within 2 m from a transmitter, and as few as 9 data points for regions farther away. This is a considerable improvement in term of computation time when compared to estimates based on approximately 4000 points, or even 200 data points. Together with GO simulations, this method reduces the initial and elaborated measurement approach to only a few simulated points and a statistical model. Finally, this methodology is extended and applied to real-world scenarios such as a long hallway and a conventional laboratory room. The agreement between measurement and GO simulation is not as good as that of the experiment conducted in a shielded anechoic chamber, but it is still reasonable, especially because the interior structures of walls such as metal studs are not modeled by the GO code. As for the statistical models used to describe the electric field strength variation in a region, it is shown that the Ricean, Normal, Nakagami, and the Weibull distributions can be employed. However, for the data collected in this work, the Normal distribution is the one that results in the worst fit to measured data for most of the cases. It is demonstrated that, even though diffracted rays are not taken into account, GO simulation allows for an accurate estimation of the parameters of a statistical model for the fast fading, for both controlled and most real-world scenarios, provided that the site geometry and electrical properties of walls, floor, and ceiling are known.