**6. Conclusion**

In this study, we measured the car-body vibration of an in-service train using a smartphone and verified whether the track condition could be diagnosed. We were able to monitor and diagnose the track condition using both the IoT device for business use and the commercially available smartphone.

The accuracy of the GNSS speed, which is necessary to identify the location of the train, was reduced by the number of satellites received by the smartphone, that is, by the number of compatible satellite positioning systems. Therefore, when selecting a smartphone, the number of supported satellite positioning systems must be considered. In addition, we determined that the performance of devices susceptible to multipath errors can be improved by performing median filtering on the GNSS speed.

Time-frequency analysis of measured car-body acceleration obtained by a smartphone shows that proper diagnosis of track condition is possible using smartphone-based track condition monitoring system.

In the future, we plan to acquire data on a continuous basis and conduct track condition diagnosis.
