@article{CBD04-tap,
	title={{Progressive and Approximate Techniques in Ray-Tracing 
		based Radio Wave Propagation Prediction Models}},
	author={Z. Chen and H.L. Bertoni and A. Delis},
	journal={IEEE Transactions on Antennas and Propagation},
	volume={52},
	number={1},
	pages={240-252},
	month={January},
	year={2004}
	}