On the Applicability of Deterministic Modelling to Indoor UWB Channels

This paper reports on the results of Ultra-Wideband measurements for several scenarios from 2 GHz to 6 GHz within an office building and investigates the applicability of deterministic modelling through 3D ray tracing to UWB channels. The blind prediction, based on the a priori knowledge of material parameters and on measured antenna radiation patterns, uses a sub-band-divided ray tracing. Measured time dispersion channel parameters such as channel impulse response in time domain and transfer function in frequency domain, delay spread, power delay profile and impulse response, have been compared with blind deterministic prediction. Moreover large-scale parameters including total path loss and frequency decaying factor have been computed for both measurements and the prediction model. 1 Objective and Introduction Basic indoor positioning systems for instance with WiFi use a database containing the signal strength footprints. Moreover, by the deployment of UWB systems the resolvability of the different multipath components has been an easier way to enable the extraction of the time of arrival. These positioning techniques usually need an extensive footprint database either of signal strength or channel impulse response [1]. Thus, channel modelling and radio coverage prediction is a solution to get a quick and cheaper alternative to the measurement campaigns. The UWB signal strength and impulse response prediction would therefore be of great interest. The UWB channel can be characterised mainly by two features which are spatial resolution and frequency behaviour. Thus, due to the higher bandwidth, a small time delay resolution can be reached and therefore certain propagation paths can be distinguished from each other. UWB signals also enable fine space resolution. Currently, UWB communication is being investigated by several research groups to provide some understanding of the UWB channel behaviour. An overview of these investigations is presented in [2]. Moreover, UWB channels are characterised by a frequency selective fading pattern. Apart from the frequency dependent variation of the antenna radiation pattern, electromagnetic material parameters show frequency selective behaviour. Propagation mechanisms like reflection, transmission and diffraction depend on the variation of the electromagnetic material parameters with frequency. In general, a power decay with increasing frequency can be assessed, the main part of power is localised towards the lower frequencies [3]. Since UWB signals do not fulfill narrowband assumptions, a modified version of the deterministic modelling with ray tracing will be presented. The main goal of this paper is the evaluation of the applicability of a deterministic modelling through 3D ray tracing to UWB channels. It is examined and discussed through measurement examples whether the deterministic modelling could be applied to predict UWB channel properties and behaviour,. This paper is organised as follows: Section 2 focuses on the deterministic modelling of the indoor UWB channel through ray tracing prediction using sub-bands combining technique. Section 3 deals with the measurements performed in office environment for LOS intra-office, NLOS corridoroffice and measurements on corridor. The applicability of the deterministic modelling for UWB channels will be examined and discussed in Section 4. PROCEEDINGS OF THE 3rd WORKSHOP ON POSITIONING, NAVIGATION AND COMMUNICATION (WPNC’06)