In a wireless channel with a large delay spread, a detection probability of conventional TDoA (Time Difference of Arrival) positioning algorithms cannot satisfy the U.S. E-911 (Enhanced-911) standard. In this paper, we propose an improved TDoA-based tracking algorithm for mobile-WiMAX (Worldwide Interoperability for Microwave Access) systems. The position of a MS (Mobile Station) is estimated by the network-based TDoA location scheme when the MS is located in the GPS (Global Positioning System) shadow area. The proposed algorithm compares the estimated position of a current state to the previous states, for achieving high reliability. Simulation results show that the proposed algorithm can improve the detection probability about 10% points, compared to the conventional TDoA-only positioning algorithm in the ITU-R (International Telecommunication Union-Radiocommunication sector) micro-cell environment, using the Pedestrian-B channel model which has a large delay spread profile. The proposed scheme's improvement helps to satisfy the E-911 standard when utilizing information from three RASs (Radio Access Stations).