 20% of the NLoS received power. ments in a dense urban area in Yokohama city, Japan, has Recent studies have shown that diffuse scattering been carried out. The transmitter (TX) and receiver (RX) plays a fundamental role in determining time and angle antennas were both mounted at a height of 3 metres in an dispersion of radio signals in the urban environment LoS street scenario. The street width was 26 metres and [DeBe99] [LKTH02]. Several authors have therefore both TX and RX were located 5.5 metres from walls on tried to include diffuse scattering effects into ray models the same side of the street. Surrounding buildings had an to improve multidimensional and wideband prediction average height of 20 metres. The measurements were performance. The first such study within COST 273 is accomplished during midnights with a very low traffic in reported in [DDGW03], where a model for diffuse the street. Employing a rotating directive antenna and scattering from surface roughness to be integrated into a sliding-correlator at the RX the authors were able to deterministic BL models is proposed. It is known that obtain a Power Delay Profile (PDP) for every DoA. some portion of the energy impinging on building walls is Analysis of PDPs revealed that most contributions arrive scattered in directions other than the specular one due to in time clusters. By comparing a precise map of the area the roughness of the surface. The scattered energy is including all present objects with the spatial distribution generally split into the so-called coherent and incoherent of received power it was observed that a significant amount components [UIMF96]. The coherent component CHAPTER 4.7 Propagation modelling and channel characterisation decreases with increasing surface roughness, whereas the The broken line in Figure 4.7-15(a) indicates the limit of incoherent (or diffuse) component becomes more sig- the validity region of the Kirchhoff model. The absence of nificant. Since rough surface scattering is generally a colour in the lower cor