Abstract
This paper presents an experimental campaign of transmission delay measurements under asynchronous condition for the communication-based train control (CBTC) systems. A three-stage asynchronous clock correction method is proposed. Before and after the working stage, the clock difference between transmitter and the receiver is calculated, moreover the relative offset and relative skew between two terminals of the working stage are derived, and it further leads towards the experimental verification of the transmission delay. In order to improve the measurement accuracy, the singular values are distinguished and eliminated in the test. Using this method, the transmission delay of the Long-Term Evolution for Metro (LTE-M) communication between the train and the signalling room in Shanghai Zhangjiang Metro Training Line is measured successfully, which demonstrates the effectiveness of the proposed one-way transmission delay test.
Highlights
In order to test the up-link and down-link transmission delay of the Long-Term Evolution for Metro (LTE-M) [1, 2], it is necessary to synchronize the clock of the personal computer (PC) between the two terminals
LTE System Structure of Zhangjiang Metro Training Line. e LTE-M standard stipulates that in the transmission of train control service, the probability of one-way singlechannel transmission delay greater than 150 ms cannot exceed more than 2%. e transmission delay test of LTE
The delay test accurately meets the requirement of transmission delay measurements for communication-based train control (CBTC), which verifies the feasibility of the proposed method
Summary
In order to test the up-link and down-link transmission delay of the Long-Term Evolution for Metro (LTE-M) [1, 2], it is necessary to synchronize the clock of the personal computer (PC) between the two terminals. One network port was used for the NTP to synchronize the clock while the other network port transmits the service data Such scheme is not applicable to the rail transit systems. Based on the wireless sensor network, a method of software skew and offset compensation [16, 17] is proposed to solve the problem of single hop direct connection synchronization between the two nodes. Apart from this scenario, the communications of CBTC go through the multiple nodes, and eventually some singular values are generated.
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