The 60 GHz Indoor Radio Channel - Overcoming the Challenges of Human Blockage (Mitteilungen aus dem Institut für Nachrichtentechnik der Technischen Universität Braunschweig)

Driven by the ever increasing capacity of storage devices and HD video streaming applications, there will be a strong demand for wireless multi-Gbps consumer applications soon. Due to its large available bandwidth and the high allowed transmit power, the unlicensed frequency range around 60 GHz is proving ideal for the realization of such systems. During the development process of 60 GHz multi-gigabit wireless systems, a detailed knowledge of the radio channel is essential. Taking into account research gaps, this dissertation makes a significant contribution to knowledge in the field of 60 GHz channel characterization. The focus is on human shadowing and its influence on the channel characteristics, which leads to a high and time-variant path loss.

In order to provide realistic results, sophisticated radio channel models are required for the 60 GHz range. In particular, they should include information in the spatial domain at the receiver and the transmitter as well as take into account time-varying human shadowing. The angular information is necessary in this case to evaluate smart antenna systems. Such comprehensive models are not yet available and therefore represent a major outcome of this dissertation. Various propagation scenarios with stationary transmitters and receivers are analyzed. The time-invariant properties are modeled utilizing a deterministic ray tracing tool. In order to validate and calibrate the tool extensive broadband channel measurements are performed. At the same time, these measurements provide information about the radio channel with respect to the angle of arrival and angle of departure properties. In addition, a the relevance of diffraction effects in the mm-wave range is studied, based on both propagation measurements as well as ray tracing simulations. Furthermore, different electromagnetic models to describe the human shadowing are analyzed in a comparative study as well as validated by measurements. Here, a self developed model should be highlighted, which is based on knife edge diffraction. It is characterized by a good agreement with measurement results and a very low computational effort. Together with the ray tracing simulator it provides a broadband time-variant deterministic channel model.

In order to make the results directly applicable for future research, stochastic models are developed in the thesis, namely a semi-static and a fully time-variant approach. The first-mentioned model is based entirely on simulation data of the deterministic approach mentioned above. The second model combines empirically obtained data from shadowing measurements with ray tracing simulation in a hybrid approach. Both complement the time-invariant cluster-based IEEE802.11ad radio channel model. The models reproduce the influence of human activity and consider up to ten people. Especially the time-variant model is the first wideband model of its kind in the 60 GHz range.

In addition to the radio channel investigations, antenna diversity concepts reducing the impairments of human shadowing are analyzed. For this purpose, the validated deterministic approach mentioned above is utilized. Finally, taking into consideration the requirements of the overall transmission system, it is demonstrated that macro diversity and beamforming is an effective countermeasure to human shadowing.