At present, indoor localization system based on ultra wideband(UWB) has attracted more and more attention. In UWB system, Time Difference of Arrival (TDOA) and Two-Way Ranging (TWR) are widely used. However, TDOA requires high-accuracy time synchronization between all anchor nodes and even slight noise can cause large localization error. In TWR localization scheme, although two-way communication between anchor nodes and blind nodes can avoid the time synchronization issue effectively, the clock drift and the number of blind nodes will affect the system performance. To overcome these problems, a new synchronizationfree TDOA location algorithm is proposed. Firstly,the clock model is established and the influence of antenna delay is considered. Then, the system signal exchange mechanism and localization model are proposed. In the system, the blind nodes just receive the ranging signals from anchor nodes so that the system has no limit on the number of blind nodes. Finally,the major factor affecting the accuracy of ranging - clock drift, is discussed, and then a clock frequency offset compensation algorithm is proposed. The indoor localization experiment results show that the indoor localization system designed in this paper can achieve 3-D localization.
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