D. Sonntag, D. Porta, and J. Setz. Proceedings of the 4nd International Conference on Mobile Ubiquitous Computing, Systems, Services and Technologies (UBICOMM-10), page 170-175. IARIA/XPS (Xpert Publishing Services), (October 2010)
T. Nestler, A. Namoun, and A. Schill. Proceedings of the 3rd ACM SIGCHI symposium on Engineering interactive computing systems, page 197--206. New York, NY, USA, ACM, (2011)