Published in IET Microwaves, Antennas & Propagation Received on 5th June 2011 Revised on 29th October 2011 doi: 10.1049/iet-map.2011.0264 ISSN 1751-8725 Modified wavefront decomposition method for fast and accurate ray-tracing simulation V. Mohtashami A.A. Shishegar Department of Electrical Engineering, Sharif University of Technology, Tehran, Iran E-mail: shishegar@sharif.edu; mohtashami@ee.sharif.edu Abstract: This study presents the modified wavefront decomposition method as a new ray-tracing acceleration technique for indoor propagation modelling. In this method, the exact propagation paths of the rays that reach the receiver after multiple reflections and/or refractions are calculated. Thus, the electromagnetic field at the receiver is obtained with a high accuracy. When only reflections are considered, our method simplifies to the multiple image theory or shooting and bouncing ray/image approach already available in the literature. However, the modified wavefront decomposition method calculates the exact propagation paths toward the receiver even if the rays encounter multiple refractions or a sequence of reflections and refractions. This novel contribution is specially important in indoor applications where through-the-wall propagation is usually noticeable. The significance of the proposed method is that the accuracy in the received field is obtained by shooting a few rays to the space around the transmitter. Consequently, a considerable reduction of the simulation time is achieved. The simulations show that the proposed method outperforms the traditional wavefront decomposition method. Furthermore, concurrent application of the proposed method and the previously published acceleration techniques is shown possible, which results in simulation time reduction of more than 11 times for a typical simulated indoor environment. 1 Introduction Accurate multipath propagation modelling in complex indoor environments is a crucial prerequisite of designing reliable wireless personal and local area networks. Site-specific methods based on ray tracing have been proven to be versatile means for characterisation of wave propagation in indoor wireless channels [1–5]. However, despite being accurate and providing deep physical insight to the propagation mechanisms, ray tracing still suffers from long simulation time. Therefore a lot of research activities have been conducted over the past two decades in order to develop a fast and accurate ray-tracing method [6, 7]. There are basically two different types of ray tracing: image method [1, 4, 5] and shooting and bouncing ray (SBR) method [2]. The most important privilege of the image method is its high accuracy because it finds the exact propagation paths from the transmitter to the receiver. However, the computational burden of the image method grows exponentially with the number of the walls of the environment [1]. Thus, its application is limited to simple environments. The SBR method, on the other hand, is computationally efficient for complex environments and can well model the refraction phenomenon. These advantages make the SBR method the preferred technique for the study of indoor propagation where through-the-wall propagation is important. However, this type of ray tracing is less accurate than the image method because of the finite number of launched rays. The combination of the two ray- tracing methods has also been reported [3, 8, 9], which tries to take advantage of the accuracy of the image method and the computational efficiency of the SBR method. However, they have not modelled refraction and therefore their indoor application is limited to one-room scenarios and corridors. In order to increase the accuracy of the SBR method, a lot of rays have to be launched from the transmitter. This, in turn, increases the simulation time. A group of acceleration techniques try to reduce the simulation time by incorporating bounding volumes or by rectangular and triangular meshing of the environment. Such methods reduce the intersection test calculations and the simulation time as reported in [7, 10–13]. In other research activities the concept of spatial super-sampling is used to reduce the simulation time [9, 14]. Nevertheless, the reduction in the simulation time is also achievable through an intelligent reduction of the number of the emitted rays as described in the next paragraph. In a previous research conducted by the authors [15, 16], it was found that in typical indoor environments a relatively large number of emitted rays do not reach the receiver and hence tracing them is useless. The wavefront decomposition method utilises this fact and reduces the simulation time in an iterative manner. In the first iteration, a few rays are emitted from the source and traced. Then the detected rays at the receiver are found. The source rays corresponding to the detected rays have transported the transmitter power to the receiver and hence are called power-transporting source rays. The wavefronts of the power-transporting source rays are then decomposed to similar smaller wavefronts, which represent higher resolution for the source. Tracing the newly generated source rays and then decomposing the wavefronts of the power-transporting ones are iteratively IET Microw. Antennas Propag., 2012, Vol. 6, Iss. 3, pp. 295–304 295 doi: 10.1049/iet-map.2011.0264 & The Institution of Engineering and Technology 2012 www.ietdl.org