Ahmed, B. T., and M. C. Ramon,  "WiMAX in high altitude platforms (HAPs) communications over large cities",  Systems, Signals and Devices, 2009. SSD '09. 6th International Multi-Conference on, pp. 1-4, March, 2009.

Taha-Ahmed, B., M. Calvo-Ramon, and L. de Haro-Ariet,  "High altitude platforms (HAPs) W-CDMA system over cities",  Vehicular Technology Conference, 2005. VTC 2005-Spring. 2005 IEEE 61st, vol. 4, pp. 2673-2677 Vol. 4, May, 2005.