A UGW communication method using Barker encoding and improved PPM for rail structural health monitoring

Given the high communication cost in the existing rail structural health monitoring (SHM) system UGW-based and no GPRS signals in the tunnel, a novel communication method in the rail based on Barker encoding and improved pulse position modulation (IPPM) is proposed in this work. Firstly, to overcome the low signal-to-noise ratio (SNR) of UGW signals resulting from dispersion and multimodal properties, Barker codes are involved in encoding excitation signals for piezoelectric ultrasonic transducers. Besides, an IPPM method is presented to diminish the multipath effect, improving communication robustness. Secondly, an enhanced communication scheme is established by combining Barker encoding with IPPM (B-IPPM). Then the feasibility and reliability of the proposed B-IPPM communication scheme are examined through simulations and experiments based on a pitch-catch mechanism. Finally, the proposed IPPM and B-IPPM methods can achieve error-free transmission, and compared to PPM and IPPM, the B-IPPM can significantly improve the bit rate (BR), achieving 1.6 times and 1.1 times the BR of PPM and IPPM, respectively. To sum up, the proposed B-IPPM modulation scheme demonstrates robust performance for the communication UGW-based in the rail.