**5.1.2 Architectural and design issues**

In this section, we describe the most important technical considerations about the BTMS. The main issues are those related to (1) trains positioning, (2) wireless 'train-to-earth' communications and (3) added value services. These three issues are described below.

1. **Train positioning system.** The BTMS permits a new way of train positioning which works independently of the main system operation. In order to achieve this target, a new hardware/software module is boarded on each train. This module combines the positioning data provided by some hardware devices (accelerometers, gyroscope, odometer, etc.) with the coordinates given by a GPS module. To generate the most accurate positioning information, this system parts from a railway lines different tabulation ways. In this case, the tabulation is related to lines lengths (in kilometres) and the traffic signals positions. Based on this information, and the data extracted from the hardware and software modules boarded on trains (including GPS), this system translates this information to kilometric points (Shang-Guan et al., 2009). Then this positioning information is sent to the control centre in real-time.

Besides, the BTMS communicates with an external positioning information system which permits the reception of train positioning information generated by the main CTC system.


The first one is a *Statistical Analysis Service*, which using the information stored by the positioning system on a data base, the BTMS can make statistical analysis related to the system's reliability level, GPS and GPRS coverage, and other system functionality aspects. Thus, one of the main goals of this service is to compare the received information, determining if the positioning provided by the train-side systems is according to the information generated by the primary CTC system. And the second is a *Control Message Exchanged Service*, which allows the procedural alarms transmission to the train-side systems. These kinds of alarms indicate anomalous situations to the train drivers: primary system failure, signal exceeds authorization to a certain point as a consequence of a failure of any electro-mechanical track component, etc.
