red with Mur 1st and 2nd AbBCs which are originated dispersive materials with ohmic losses, along with the from one-way wave equation like Liao's AbBC. The ar- solutions to the problems on the D source excitation. tificial reflection coefficients from the proposed AbBC [CoTh04a] detailed a method of dealing with the CFL and Mur 1st AbBC were in a comparable order, while the stability condition in a lossy medium for UWB systems, Mur 2nd AbBC showed the best absorption among these utilising the frequency spectrum of the source excitation. three boundary conditions. On the other hand, the The error in the lossy case was proved to equal the analysis of the frequency reflection coefficient proved lossless case with an appropriate NCFL adjustment. It is CHAPTER 4.7 Propagation modelling and channel characterisation shown that FD-ADI-FDTD is applicable for problems which can accommodate error higher than 0.1 with NCFL > 6, gaining a simulation time benefit over FD-FDTD. Although the merit of FD-ADI-FDTD is the absence of a limitation on the value of At for stability, which allows the reduction of elapsed time of FD-ADI-FDTD, com- pared with FD-FDTD, the accuracy reduces this merit by a certain amount because accuracy largely depends on the temporal discretisation and spatial discretisation. Therefore, a method to set an appropriate At in UWB systems is also inductively proposed [CoTh04b]. Range km Parabolic equation methods The Parabolic Equation (PE) method is based on a para- Figure 4.7-5 Path loss for standard troposphere conditions. xial approximation to the wave equation. Assuming that the fields propagate in a preferred propagation direction, minima. At those minima, the differences between the this is a full-wave method accounting simultaneously and case with the standard troposphere and the ducting case accurately for all wave phenomena like diffraction, re- may exceed 20 dB for a ducting layer of 50 m thickness. fraction and scattering. Provided the field is known on an Paper [SiMi03] discusses the influence of