## Predicting multipath distortion

#### In order to design wireless digital communications systems that can best cope with the multipath environment in which they must operate, it is very helpful to be able to predict and simulate these effects in the system design phase. Apart from statistical prediction tools based on extrapolations from measured propagation data, one of the most accurate and versatile modelling techniques is based on ray-tracing. |

#### In a ray-tracing system, the reflective, refractive and dispersive properties of physical objects are modeled within a computer, along with their three-dimensional position. Every possible path that could be taken by a signal passing from transmitter to receiver is then traced by the computer, building up a picture of the level, angle of arrival and time delay of each one. From this information, it is possible to determine the frequency response of the channel, and to simulate the effects of the multipath fading on actual modem performance. This technique is very similar to that used to produce real-world lighting effects on virtual 3-D models created in a computer.

####