The Needs for Services to Passengers
Introduction to Internet on Board Trains
Current public telecommunication services increased the needs of mobility services. Indeed, wireless communications have been deeply integrated into people’s life. Peoples are more and more demanding in terms of transmission rates. High Speed Downlink Packet Access (HSDPA) allows throughputs up to 28 Mbps using 5 MHz of bandwidth. Currently, Long Term Evolution (LTE) is largely deployed all around the world. Theoretical throughputs can reach 300 Mbps on a 100MHz bandwidth. All these recent evolutions concern also the transportation domain .
Many recent technological advances were observed: a miniaturization of devices, an ergonomic use of the devices, the development of wireless communications between the devices, the significant increase of data transfer and the multiplication of functionality of the devices .
It is also important to note that railway domain is a more and more competitive environment and it becomes important for railway operators to make travel more comfortable and pleasant by offering new services or by improving existing services relying on telecommunications. The main commercial service is the Internet access on board trains. We then focus on this subject in this part dedicated to services to passengers.
The first solution for providing broadband Internet access on board trains could be that users directly connect their devices (smartphone, laptop, tablet) via their own mobile operator [7, 51]. However, this solution requires appropriate cells management and ability, and sufficient radio coverage along the railway line. Indeed, public networks design does not take always in consideration the railways network. In addition, as already mentioned, the metallic structure of carriages behaves like a Faraday cage, which causes signal attenuation up to 15 dB, and even 30 dB in worst cases . To overcome this problem and improve performance, repeaters may be installed on trains. However, installation and maintenance of these repeaters involve significant costs. Furthermore, performance of these transponders depends closely on the quality of the radio coverage: the amplification of a weak signal causes a low SNR and therefore a “bad quality” amplified signal. Some experiments were performed in 2007 by Sauter . The experiment corresponds to a direct connection of a terminal in the train via HSDPA. The tests were performed on a German Intercity Express (ICE) HST from Paris to Frankfurt. Peak throughputs of 1.5 Mbps and average throughputs of 850 kbps were observed. However, communication failures are often encountered. It is clear that other solutions need to be developed.
Internet access on board trains is not a standardized technology yet. A lot of different solutions and architectures were then developed to bring Internet on board trains . Finally, regarding required bandwidth, if we consider that a train contains typically 1500 passengers, the bandwidth requirements of several Gbps per train is not unrealistic .