In the development of new indoor wireless communication, a versatile and accurate radio channel model for indoor is needed. This paper proposes a more efficient 3D propagation model to predict a indoor propagation characteristics. Ray tracing method based on image method is used in this model. 3D model can predict any complex indoor environment composed of arbitrary shaped walls. It finds all propagation paths from a transmitter to a receiver extensively and it is a point-to-point tracing method, so reception tests are not required and it gurantees high accuracy. It considers the effect of neighbouring building for more accurate prediction. Using this model building penetration loss is predicted. To predic efficiently, this paper propose a speed-up algorithm, rectangular ray tube method and use a threshold level.
