Abstract: The Universal Mobile Telecommunications System (UMTS) under development in the international community has been agreed to include both terrestrial and space segments as integral parts of the system. The purpose of the SINUS project is to demonstrate that UMTS services can be provided seamlessly via satellite, and to make recommendations concerning the interworking between space and terrestrial segments. The SINUS laboratory system demonstrator is being developed to illustrate the role of the Satellite–UMTS, including a real‐time emulator with programmable perturbations in the link to the mobile user, representing all expected satellite constellation and mobile link characteristics. The Mobile Terminal and Fixed Earth Station (FES) consist of CDMA modulator/demodulators for satellite‐specific communication functions, and also include software for more generic UMTS network functions (e.g., call management, mobility, handover). To demonstrate the realistic operation of the system, several examples of multimedia applications will be implemented from end to end.