Error-Correction Coded Orthogonal Frequency Division Multiplexing Track-Circuit Transmission

Abstract

In railway train control, when the track is used as a communication channel for control information, it is necessary to transfer the control information while avoiding the interference of the noise caused by the train drive current flowing through the track. With regard to the characteristics of noise, in this study, we focused on the discrete harmonics, frequency variation of commercial power sources, and switching noise from the onboard inverter. The modulation of the control information adopts orthogonal frequency division multiplexing (OFDM), which employs multiple narrowband carriers simultaneously. Because the noise appears as a line spectrum, even if a communication error occurs in the noise carriers, the error is corrected, thereby increasing the communication speed. Our previous study demonstrated that a simulation using the Read-Solomon code yielded an error correction code (ECC). Recently, codes such as turbo codes and low-density parity-check (LDPC) codes, have been adopted as ECCs; however, thus far, no method has been proposed for the safe use of these codes. In this study, we consider this problem, and demonstrate the concept of eliminating the interference of the train-driven current noise due to the OFDM modulation using ECC when using a track circuit for information transmission in train control. To reduce the probability of miscorrection, the process that determines the number of corrected errors is introduced in the receiver, and the safe use of the ECC is demonstrated.