High-speed core networks with optical fibers are globally being installed. However, it is very difficult to access these core networks from rural districts such as remote places among mountains and solitary islands. Synchronous CDMA systems with GEO satellite links are very attractive to solve this problem, since such systems have wide service areas and are suitable for packet-based networks due to their statistically multiplexing effect. Furthermore, their statistically multiplexing effect leads to effective frequency and power efficiency. In synchronous CDMA systems, each transmitted signal from a fixed earth station must be controlled to be synchronized with each other. However, the broadband systems require extremely precise timing control. In this paper, we discuss synchronization methods and evaluate their timing accuracy for the broadband systems quantitatively. First, we point out defects of two fixed filter methods and a Kalman filter method. Then, we propose a new synchronization method, which is robust to random noise and trend components. As a result, we conclude that the proposed synchronization method can make it possible to synchronize lGchip/sec CDMA systems with GEO satellites.