Research On Key Technologies Of Wireless Time Synchronization For TC-OFDM Indoor Distributed System

TC-OFDM system is a wide area high-precision wireless network positioning system,which can provide seamless and high-precision location service in indoor and outdoor environment.TC-OFDM wired indoor distributed system and wireless indoor distributed system are responsible for broadcasting positioning signals in indoor environment.For the convenience of layout and maintenance,wireless indoor distributed system is usually used to set up large venues.TC-OFDM system requires high-precision time synchronization between signal sources,but there is no direct physical connection between signal sources in wireless indoor distributed system,so it is necessary to provide time synchronization service for wireless indoor distributed system.The main research results are as follows:1.The delay in the critical path is difficult to estimate accurately,which is the root cause of poor scalability and large cumulative synchronization error of wireless time synchronization algorithm.This paper proposes a critical path delay elimination time synchronization algorithm for large-scale network(CPDE).CPDE uses the physical layer timestamps of UWB and two way time message exchange to eliminate most of the delay in the critical path;uses the timestamps of two way time message exchange to construct data pairs,and uses the least square method to update the logical clock drift and logical clock offset;proposes the logical clock drift update control mechanism to reduce the impact of the remaining delay on the time synchronization accuracy in order to improve the performance of time synchronization algorithm.2.Due to the loss of time messages in complex channels,it is impossible to obtain complete timestamps,which leads to the problem that the time synchronization period becomes larger and the time synchronization accuracy is reduced.This paper proposes a robust CPDE algorithm(RCPDE).If the node can not obtain the timestamps due to the loss of time messages,RCPDE algorithm uses Kalman filter to estimate and predict the clock offset and clock frequency offset,and modifies its own clock according to the predicted value,or RCPDE algorithm calls CPDE algorithm to calculate and update the logical clock drift and logical clock offset.3.The prototype of wireless indoor distributed system node is developed,which is used as the verification platform of time synchronization algorithm to test the average network error and hop by hop average network error of time synchronization algorithm.The experimental results show that the proposed CPDE algorithm significantly reduces the cumulative synchronization error and improves the scalability of the time synchronization algorithm;in complex channel environment,RCPDE algorithm can reduce the impact of time messages loss and improve the robustness of time synchronization algorithm.