Ahmed, B. T., and M. C. Ramon,  "Downlink capacity and interference statistics of wideband code division multiple access microcells for trains in long tunnels",  Communications, IET, vol. 3, no. 4, pp. 603-609, April, 2009.

Ahmed, B. T., M. C. Ramon, and de. Haro L Ariet,  "Comments on the hybrid model for propagation loss prediction in tunnels",  Antennas and Propagation Magazine, IEEE, vol. 45, no. 5, pp. 156-158, Oct, 2003.