Development and Evaluation of CDM-QAM Transmission Devices for Track Circuit

At present, in Japan, railway signaling systems in which control information is transmitted via rails have been deployed in many applications such as automatic train control (ATC) systems for controlling train speed. Recently considerable R&D has been conducted on digital ATC systems realized by applying digital modulation methods such as minimum shift keying (MSK), and such systems have been installed in some railway lines in urban areas. However, it is difficult to increase the transmission speed owing to the railway noise and the strong attenuation of the track circuit. Therefore the present transmission speed is approximately 300bps. To overcome this problem, we have proposed a new modulation method combining code-division multiple (CDM) and quadrature amplitude modulation (QAM), called the CDM-QAM method. Further we have studied the effectiveness of the CDM-QAM method by conducting computer simulations. In this paper, we developed CDM-QAM transmission devices using digital signal processors (DSPs) and field programmable gate array (FPGA). In addition, we evaluated the performance of the developed devices on the basis parameters such as the bit error rate (BER) characteristics of the measurement environment which was configured to include railway noise.