Modelling of wireless channels and validation using a scaled mm-wave measurement system.

Abstract

The design and fabrication of a W-band coherent transmission measurement system for measuring characteristics of wireless channels under laboratory conditions is presented as an alternate approach to time consuming and expensive outdoor measurements. The signal frequency of the transmission system is chosen to be much higher than most commercial and military wireless systems so that the size of the scatterers can be made sufficiently small. Frequency scaling from the L-band to the W-band allows for size reduction (scaling) of a city block down to two orders of magnitude. First the overall system concept based on a very sensitive stepped frequency coherent transceiver system is introduced and the specifications of each system block are presented. For miniaturization the W-band up- and down-converter probes are designed monolithically. All microwave and millimeter-wave system components are fabricated, tested individually and then incorporated into the scaled measurement system. The overall system performance in terms of system dynamic range, noise floor, minimum detectable signal, and system calibration are also determined and reported. It is shown that with this system a signal as low as -125 dBm, and a maximum pathloss of 100 dB can be measured accurately. Delay profile resolution of 0.5 ns corresponding to 2 GHz system bandwidth can also be measured at W-band. A reconfigurable scaled urban environment is also made using a precision 3-D printer machine developed by Z-Core. Building materials are made up of plaster and glue whose dielectric properties at W-band are measured using a wideband coherent free-space transmission measurement method. The system developed in this research is of its first kind with significant experimental capabilities for characterization and validation of wireless systems. A physics based site-specific channel model using a 3-D ray-tracing algorithm is also introduced. The model is used to analyze wave propagation in complex urban and suburban environments. The application of this simulation tool for through wall imaging using a time reversal method is also demonstrated. This model is also validated using the scaled measurements system for a variety of urban scenarios. Excellent agreement between simulation and measurements indicates the high accuracy of both the measurement system and the ray-tracing simulation model.