Everyone will have come across a frequent problem at least once when traveling by train: the poor reception mobile phone signal while traveling. This aspect, which some may appreciate, makes the travel experience less pleasant for many passengers, especially when they need to stay connected for personal or professional reasons. But why don’t cell phones work well on trains? We analyze the technical and environmental factors that influence signal quality during rail travel.
Possible causes of signal attenuation
Among the causes that can attenuate the cellular signal in the train, there are structural factors, concerning the materials with which the trains are made, but also linked to physics of electrical signals and, last but not least, the distribution of antennas radio along the railway networks and in the presence of obstacles natural and artificial between the antennas and the train. Let’s briefly analyze these aspects.
Construction materials
Steel, aluminum and other ferrous materials constitute the fundamental part of the structure of modern railway vehicles, to guarantee robustness and safety. While these are essential to give solidity to the structure of the train, they act as “barriers” for radio waves. The physical phenomenon that is generated, in fact, is known as “Faraday cage“: in short, the metal structure of the train performs an action shielding towards electromagnetic waves. This prevents to the cell phone signal to penetrate inside the carriage. Windows can also be made with coverings metal, in order to improve energy efficiency and, also in this case, robustness. While they could normally represent an access route inside for electromagnetic waves, these measures reduce the effectiveness of penetration inside the train.
The Handover phenomenon
Mobile phones connect to specific cells within the mobile network. When a user moves, the device switches from one cell to another through a process called “handover”. On trains this process has to happen a lot quickly, and this is true the more the train travels at high speeds. Mobile networks may not always be able to handle these handover frequent, which causes signal interruptions.
Doppler effect
Another important aspect to consider related to movement of the train is the effect obtained on the electromagnetic waves. The movement at high speeds compared to the radio antennas generates the so-called “effect Doppler”, altering the frequency perceived by the device. It is analogous to what happens when we hear a siren from a moving ambulance: while the vehicle heads in our direction with its sirens blaring, we will perceive a louder sound. intense while, once beyond our position, the signal will appear gradually subside. This also happens with radio waves and can interfere with your phone’s ability to maintain a stable connection to the network.
Network coverage along railway lines
Rail lines often pass through rural or sparsely populated areas: in these areas, the density of mobile phone antennas is minor and, as a result, signal coverage may be poor or absent at all, regardless of train speed or carriage design. During their runs, trains are often also found passing inside tunnels or areas where they are present obstacles natural such as mountains and hills. These physical barriers can divert, attenuate or block the signal completely, making mobile communication impossible on these routes.
Electromagnetic interference
Even the electrical systems necessary for monitoring of the parameters train operation can cause interference with cellular signals received from our smartphones: especially in modern trains, complex electrical systems are used to operate the engines and internal systems.
Just as it could happen during a football match or a concert, even inside a crowded train the presence of a high number of mobile devices can compete for the same bandwidth: this causes network congestion and degradation of the service for all users on board.
Technological solutions and possible improvements
If, on the one hand, it is true that there are various factors that can hinder the signal, it is equally true that various solutions can be implemented to resolve these inconveniences.
Installation of signal repeaters
Some railway companies have begun to install signal repeaters inside the trains. These devices they amplify the external cellular signal and spread it inside the carriage, improving reception for passengers.
Wi-Fi on board
An alternative to the cellular connection is the use of WiFi offered directly from the train. This service often uses connections satellite or mobile networks enhanced to provide internet access to passengers, bypassing some of the problems associated with cellular signal reception.
Mobile network improvements
While mobility service providers can take some actions, mobile operators are also constantly working to improve coverage along railway lines, installing more antennas and optimizing networks to better handle devices moving at high speed. The use of technology 5Gfor example, guarantees higher speeds and lower latencies than previous generations. This technology is also designed to better manage your devices movement rapid, thanks also to the use of advanced antennas with the ability to beamforming. These are capable of “focus” the signal directly towards the moving device, a bit as if it were a radar tracking a target. This ultimately improves connection stability even at high speeds.
