Improvement of an UGW-based track circuit for operation on repaired railway sections

Ultrasonic guided waves (UGW) signals have been applied to high-speed railway lines to detect the status of track sections in China for many years. Though the UGW detection systems have many advantages, the UGW signals cannot propagate through the railway gap caused by a track breakage, thus becoming unsuitable for these situations. This work proposes an improved track circuit based on a previous UGW detection system, which is able to solve the mentioned drawback existing in mended rails. The proposal is based on the use of 63-bit Kasami sequences in the transmission encoding, in order to improve the capability to collect information about the track section, and to get a higher noise immunity. The high auto-correlation functions (ACF) and reduced cross-correlation functions (CCF) from Kasami sequences have allowed these improvements, providing a good performance in signal detection at receivers.