Performance evaluation of an ITS system integrated with complementary LEO mobile satellite system A novel 2-tier integrated communication system is proposed to address the issue of unavailable Road Side Unit (RSU) in Intelligent Transport System (ITS). Compared to some other solutions proposed in the previous research works, which mostly focus on improving the system performance by adjusting parameters of vehicular ad-hoc network among vehicles, the proposed 2-tier communication network, called ITS-LEO Integrated System (ILIS), is composed of conventional ITS system and Low Earth Orbit (LEO) mobile satellite system (MSS), where the LEO MSS is utilized as the complementary networkwhen RSU is unavailable. A real-time simulation program in C++ is developed to evaluate the performance of ILIS in terms of Packet Loss Rate (PLR). The simulation results show that adding LEO MSS as a complementary network to ITS is an effective way to solve the problem of unavailable RSU.