Mobile positioning is becoming an important service on radio cellular network. Among different kind of location estimation technologies, the one which estimates the location of mobile stations using signal strength is able to be applied to different kinds of cellular network, and therefore, is more general. We have designed a directional propagation model - the Ellipse Propagation Model (EPM) which makes use of a wave propagation model to perform location estimation. The EPM enhanced the traditional propagation model by resembling the contour line of signal strength as an ellipse rather than a circle and hence becoming more realistic. We have tested the EPM with real data taken in Hong Kong and it is proven that the EPM out performing other existing location estimation algorithms in different kinds of terrains.