## 1 Introduction  
Modern railway systems follow trends in the automotive market: The modern traveler expects to be offered services such as onboard entertainment, high-speed internet connection, detailed information about the trip and so on. In addition, nowadays, the increase in the need for onboard safety leads to the requirement of onboard cameras located in each hauled stock. All this new equipment requires more dedicated cable networks but is characterized by the following drawback: New cables mean additional costs, weight and space (the latter ones being secondary problems in railways systems if compared to cars, airplanes or satellites). This holds for new trains, while for old trains (for instance, regional trains), the revamping procedure could be extremely expensive, basically making it impossible to be realized. The use of a broadband power line (BPL, or high-speed power line communications, PLC) in vehicles is an application that has been investigated by many researchers lately (see, for instance, [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13]), showing that this technology could be of great help in reducing the need for cable harnesses. The research for in-vehicle PLC is largely devoted to automotive and electric cars [1; 2; 3; 4; 5; 6; 7; 8], and in part to other vehicles such as ships [8; 9; 10; 11] and aircraft [12; 13; 11]. The use of PLC technology to communicate with high-speed data rates over the UIC cables was a novel proposal by the authors, and the literature on PLC onboard trains is scarce. In this context, this work presents a complete characterization of the channel, extending and completing previous work where the authors already performed a feasibility study and selected a potential candidate cable for carrying the broadband signal, mainly the UIC cable comprising the remote control and communication line ([14; 15; 16; 17]). The rationale behind this choice is the following:  
1. This electrical connection is extremely common in hauled stock and it is unified by regulation [14]. 2. It connects the whole length of the train and, for safety and functional reasons, particular care should be taken to avoid any possible disconnection. 3. Its use could lead to an easy procedure for revamping older trains at a reduced cost. 4. In [15; 16], the cable has been tested and its electrical parameters have been measured and simulated; in addition, some simulations relating to data transmission are shown. 5. In [PERSON] et al. [17], the authors evaluate the channel capacity (hence the maximum data rate available) as a function of the noise produced by the other signals carried by the cable. The above described cable is a multiconductor transmission line and the crosstalk phenomena can create undesired voltages and currents which might disrupt either the BPL signal or the other signals. This paper is based upon [PERSON] et al. [15; 16; 17], but the current paper includes the following additional research: a full multiconductor formulation for the evaluation of the frequency response and the crosstalk is used and described in detail, and the obtained frequency response is analyzed in depth, evaluating the delay spread and the cumulative distribution function of the frequency response attenuations. Additional research carried out and discussed in this work includes an evaluation of the bit error rate (BER) using a QPSK-OFDM (quadrature phase shift keying-orthogonal frequency division multiplexing) modulation scheme, giving us an indication of the degradation of the BER with distance. A detailed analysis of signal propagation is carried out in this work, taking into account the characteristics of all the signals carried by this cable during regular train operation, with the scope of assessing the real feasibility of such an application, ensuring that both new signals (used for example for infotainment) and standard signals carried by the cable do not interact with each other.