Some of the system level related papers addressing the wireless telecommunication systems is presented in the special issue of Annals of Telecommunications, which has been assembled from a set of oral presentations made at the 13th European Wireless Conference, Paris, France, April 1-4, 2007. The first addressed topic by Misha Dohler, Thomas Watteyne, Fabrice Valois and Jia-Liang Lu, describes fundamental scaling aspects of ad-hoc networks with a very large number of nodes. The second paper by Patrick Marsch and Gerhard Fettwe analyzes cellular networks. Yikang Xiang, Jijun Luo, Egon Schulz and Carmelita Görg show why inter-cell interference in OFDMA networks is expected to be a key limiting factor of performance. The last article by Michel Sortais, Sven D. Hermann and Adam Wolisz show why the localization of mobile devices is essential for the provisioning of location based services.