Internet on Board

All methods of transportation nowadays offer the possibility for passengers to connect to the internet. This is important for passenger comfort; passengers want to work, read, stream videos and communicate with their friends and families. But passenger comfort is not the only argument for an active, constant connection to the internet – it is crucial for the safety of the vehicle, and therefore the safety of the passengers. In case of an emergency, the vehicle needs to exchange data with a command post in the outside world. Only then can they provide the vehicle with information and support. A third reason for the need of internet on board, is the guidance of the vehicle. To update the location, the speed and other data about the vehicle status and telemetry data, it is essential to ensure a stable internet connection at all times.

Challenges

As written in the intro, a constant connection to the internet is a requirement for a safe and comfortable trip. Since this is a target for hyperloop transportation as well, one can conclude that the moving pods in the hyperloop should to be connected to the internet. However, establishing this requirement for the hyperloop comes with unforeseen challenges, since these aspects are unique for hyperloop, and therefore not present in the current modes of transportation. 

  1. Establishing an active internet connection at high speeds
  2. Establishing an active internet connection through the steel tube

The High Speeds

Unlike a train or a maglev, the hyperloop will move with much higher velocity. Although it will probably reach greater speeds than airplanes, overcoming this challenge can be inspired by them. Within the tube, pods could theoretically communicate with each other by any means of wireless data communication (e.g. via radio waves). At high speeds however, a new problem occurs: the shift in frequencies and wavelengths. This phenomenon is also known as the Doppler effect, and it occurs when the source and the observer of a signal move with a relative difference in speed. The frequency or wavelength changes in relation to an observer who moves relative to the source. This is the reason why the sound of a siren changes when an ambulance drives by. Because of the Doppler effect, wireless data communication between pods comes with a lot of trouble.

The Steel Tube

One major issue is the thick layer of steel that divides the moving pod and the open air. Currently, there is no wireless communication technology (e.g. 4g, radio waves) that is able to penetrate steel. That leaves two options to tackle this problem: 

  1. Wait for the arrival of wireless communication technology that can communicate through the wall
  2. Combine wired- and wireless communication to surpass the steel tube

Development of 5g

Current technologies for wireless communications do not satisfy the needs for the hyperloop. Fortunately, there is a promising new development in the communication technology: 5g. 

5g is the fifth generation of mobile network. It is the sequel of 4g, the current main technology for wireless communication (that you probably use everyday with your mobile phone). Potential improvements with respect to 4g relate to speed, latency and the ability to pass walls. However, 5g is still in development. It is yet unclear when the 5g network will arrive, and whether is will be able to pass through the thick steel tube.

Combining Wired- and Wireless
Communication

Wireless communication through the tubes wall is currently not possible. However, within the tube, there is no such problem. Therefore, a pod can communicate instantly with every point within the tube.This knowledge can be combined with tactically placed receiver points in the tube, that can receive data from the pod via any form of wireless communication. This opens a path to communication from a pod to the outside world. Wires could be placed through the walls of the tube, connecting an antenna (or any other type of data receiver) with an antenna (or any other type of data broadcaster) outside of the tube. The data then can get forwarded to anywhere outside of the tube. This system is a combination of wireless and wired communication, and it allows the pod to interact with other pods in the tube, and with the external world. The image below gives a representation for the communication mechanism. The pod sends data via an antenna to another antenna in the tube. This antenna forwards the data to the antenna outside the tube, via a wired connection. Then, this antenna can send the data out in the external surrounding. 

Communication scheme for the hyperloop
Figure 1: Representation of the communication scheme.
  1. Internal communication: pod to tube
  2. Wired communication through the tube via fibre
  3. External communication: tube to external surrounding 

Wires

These wires should have three main qualities:

  • Bandwidth 
  • Latency
  • Maintenance cost and time.

One type of wire that features all of these qualities is optical- or glass fibre. The current state of fibre implies that it is fast enough,  and the bandwidth is sufficient. Moreover, fibre is evolving. The coming generations will improve in all the mentioned aspects.

Conclusion

Communication, both within the tube as between the inside and outside of the tube is an essential aspect for safety and comfort. The communication aspect for the hyperloop is challenging; both the internal and external communication. Internal communication has to deal with Doppler effect. External communication needs to surpass the thick steel tube. These problems can potentially be solved by the application of a combined wired-wireless communication system, and with new upcoming technologies.

By Delft Hyperloop, June 2019

3 Comments

  • Emile Pels

    Nice write-up of an interesting problem that’s essential to designing a hyperloop at scale. I’m curious: was FSO (free space optical communication) considered for communication? I’m not fully sure how this performs in terms of the Doppler problem, but this type of communication is often used in communications for other aircrafts: perhaps this can be a useful technique for internal communication. Furthermore, I can imagine this technique can eventually be utilised to establish internal-external communication, effectively bypassing the need to have a physical/wired connection from inside the tube to the external world.

    • Delft Hyperloop

      That’s an interesting thought! FSO does seem promising for internal communication. However, For FSO communication, a clear line of vision between the source and the observer of the signal is required. In a hyperloop tube, this depends on the headway between moving pods. Regarding the external communication, FSO can not surpass the steel tube. Therefore, the external communication should still implement the combined wired-wireless system.

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