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Path loss model for ultra wideband signal propagation

Ultra wideband (UWB) systems facilitate high data rates over short distances. Path loss is considered to be a fundamental parameter in channel modeling, since it plays a key role in link budget analysis. Also, path loss determines the robustness against interference and noise, which in turn influences the bit error rate behavior. Narrowband path loss models are not applicable to the path loss calculation of UWB systems. UWB transmissions occupy bandwidths of up to 7.5 GHz in the radio spectrum between 3.1 GHz and 10.6 GHz. The path loss frequency dependence cannot be ignored within such a wide band. In addition, the distance between the transmitter and receiver is assumed to be considerably less than that of traditional wireless systems. An indoor operating scenario with a range of up to 10 meters is often considered. Hence, the approximations held in a large scale are invalid and it is often required that path loss and signal degradation are handled in some scale at same time. Unprecedented wide bandwidths and short ranges require a novel approach towards the link budget calculation and channel modeling. The two-ray model is utilized extensively since it offers a simple tutorial and can produce representations of most of the behavior from practical channels. In this paper, a rigorous formulation of a two-ray link is considered and evaluated as a function of both frequency and distance, where all the assumptions adopted for deriving the traditional narrowband plane ground model are no longer valid. Considering the specific UWB application, the analysis is carried out over distance of up to 10 meters and in the operational frequency band of 3 GHz to 10 GHz. From this study, both the one- and two-slope analytical path loss models for short range, two-ray links with wide operational bandwidths are derived, which are considered to be good approximations for line-of-sight (LOS) UWB links operating in a relatively clutter-free environment. On the basis of this, the frequency and distance characteristics of the path loss are discussed, and some meaningful conclusions for UWB system analysis and design are drawn.