This paper proposes an autonomous decentralized synchronization system for Inter-Vehicle Communication Network (IVCN). We have to consider the future of IVCN: "time variant" about the number and the location of vehicles in IVCN, frame timing, and fading. Proposed scheme is different from other decentralized synchronization systems that have association with a fixed base station, and from centralized Personal Communication Systems. This system includes an autonomous decentralized synchronization scheme for IVCN, a high-speed algorithm, a protocol for a coming subscriber in IVCN, and a utilization of spread spectrum ranging for frame timing error. Computer simulation evaluates the performance of the system under highway conditions. It is shown that IVCN can be carried out among one and surrounding vehicles in such environment.