A new 3D indoor ray-tracing propagation model with particular reference to the prediction of power and delay spread

Publisher Website
Google Scholar
Abstract
In this paper a three dimensional 'image- based' ray tracing algorithm for indoor environments is presented. The model is capable of predicting wideband as well as narrowband propagation information for single floor scenarios. To show the practicality of such a model, the ray tracing engine has been used to investigate a typical indoor environment. The influence of internal objects such as windows, doors and partitions is considered. Since externally reflected and diffracted rays are supported, the impact of external building structures on the received power and rms delay spread is examined. The channel characteristics were also studied for different receiver antenna orientations. I. INTRODUCTION The need for more accurate propagation models will increase as indoor communication systems continue to evolve. Due to the site-specific nature of these environments, tools are required which take into account the location, the orientation and the electrical properties of individual walls and objects. At present, it is unlikely that existing empirical models will yield the accuracy and information required for future indoor planning. With this in mind, more attention is now being given to the development of indoor site specific propagation tools. Ray tracing produces deterministic channel models that operate by processing user-defined environments. It represents the high frequency limit of the exact solution for electromagnetic fields and can give good approximate solutions when it is impractical to obtain exact results. In this paper an 'image-based ray tracing model is presented that allows the rapid generation of complex channel impulse response characteristics for any given location of transmitter and receiver. In the algorithm, the image generation operates in two dimensions. However, for each two dimensional path, all the corresponding rays are then calculated in three dimensions including multiple floor- ceiling reflections. Factors such as polarisation and three dimensional antenna patterns are fully considered in the model for any antenna orientation. The simulation makes full use of reflection, transmission and diffraction and is capable of supporting indoor objects such as doors, windows and partitions. Moreover the model provides the ability to consider the influence of external building structures on the predicted indoor characteristics. 11. MODELLING APPROACH THE IMAGE TECHNIQUE: Ray tracing represents electromagnetic waves as rays which are generated from a transmitter and launched in three dimensional space. There are many types of ray-tracing techniques reported in the literature (l-61. In this model a technique based on the electromagnetic theory of images has been developed. Rather than using a 'ray launching' approach where rays are sent out at various angles and their paths traced until a power threshold is reached, the technique adopted here considers all walls and obstacles as potential reflectors and evaluates the location of their transmitter images (2). This imaging technique works by conceptually generating an image table for each transmitter location. This process is implemented by considering all the various wall reflection, transmission and diffraction permutations that are possible in a given area. The image information is then stored in an array and used to compute the channel characteristics at each receiver location. To allow three dimensional paths to be found, a vertical ray trace is performed based on the results of the horizontal two dimensional image map. The situation for the simple line-of- sight case is illustrated in figure 1. The appropriate three dimensional rays can be calculated by considering the heights of the transmitter, receiver and ceiling.

This publication has 8 references indexed in Scilit: