Experience with on-board unit communication in public transportation

Experience with on-board unit communication in public transportation

This article summarizes our experience with implementing various vehicle communication systems that communicate with other systems in public transportation – communication with dispatching, checking, depots, passengers, and technologies on the route including V2X.

Data flows in the transportation system

Arrangement based on data flows:

  • Control (OC) – data for on-board computers and drivers – usually schedules, traffic closures, manuals, instructions, traffic data, dispatching communication, maps, …
  • Information systems (IS – mechanical, LED, LCD, e-paper, …) – usually video spot related data
  • Checking systems (EOC) – synchronization of tickets with  regional accounting center, on-line payments by card, forwarding tickets to other connections
  • Camera systems (CS) – on-line transfers to a supervision center and off-line transfers of incidents, supervision data
  • Tachographs (TT) and vehicle behavior information transfers – sending data about vehicle behavior, daily records, on-line data
  • Passenger counting systems (APC) – on-line data about the number of passengers, vehicle logs for further assessment
  • WiFi for passengers – usually an independent communication channel separated from other vehicle data communication
  • V2X communication systems – providing PT vehicle preference including warnings sent out to the surrounding area
  • Independent advertisement systems (independent advertisement media) – their characteristics are similar to LCD, but they do not contain transportation information
  • Switches – usually a system of automatic throwing
  • Other systems – e.g. for the vision impaired …

Data flows in a transportation system.

Internal vehicle communication

Moving this communication to an Ethernet busbar of up to 1 Gbit/s

  • Internal vehicle communication.

    Internal vehicle communication.

    Unified protocols – in Germany IP IBIS, our EPISNET – used by 3000 on-board computers

  • Routers in vehicles – separation of networks
  • Building more types of eth. network in a vehicle for the reasons of security and operation separation e.g.
    • Information and checking system
    • Camera system
    • Joined vehicles
  • IBIS – cheap –now only for controlling tableaus and command receivers
  • RS 485 – specialized – usually low-consumption sensors, throwing of switches, ….
  • CAN – suitable for reading vehicle states
  • RS 232 – used mainly for radio network control
  • USB – records, updates

External vehicle communication

  • GSM/LTE – once, twice or more in one vehicle
  • Radio networks (PMR) – digital (DMR or TETRA, analog) -
  • Vehicle to surroundings communication
    • WiFi
    • V2X
    • The vision impaired – free band – reserved for this purpose
    • throwing of switches (VETRA, BSV, other)
    • Chosen types of low input power communication (FHSS)
    • Short range communication
    • NFC, proprietorial solution and payment cards
External vehicle data communication.

External vehicle data communication.

Vehicle communication arrangement

The following description concentrates on communication from the point of view of external management of systems but not from the point of view of “internal” vehicle communication supplied by the vehicle manufacturer. Such arrangement can be:

  • Centralized communication arrangement (1 SIM card) controlled by an on-board computer, acting as a basic vehicle communication channel to many servers – usually via APN.
  • Shared communication (1 SIM card) provided by a vehicle communication unit that other systems use to communicate.
  • Managed island systems (independent SIM cards for individual vehicle systems), while activities of these systems are coordinated by information from an on-board computer.
  • Independent island systems, when data from individual systems is managed and processed by external servers.

Centralized communication arrangement

The basis of this communication is that all the systems used in a vehicle communicate via an on-board computer and the on-board computer is the fundamental control element of the vehicle. The on-board computer is the fundamental communication unit and it provides:

  • Firewall protection and data router function
  • Possible connection via APN or public internet (APN is more secure)
  • Management of component and system updates that are provided by the supervision system of the operator
  • Advantage of a higher system security – everything can be done in one place, utilization of secure protocols and rules
  • So called empty garages for updates of other systems that get updates from supplier or manufacturer servers
Vehicle connection.

Vehicle connection.

An example of a centralized communication arrangement using an on-board computer communicating with multiple servers – typical for regional public transportation:

Centralized communication arrangement.

Centralized communication arrangement.

  1. Checking and vehicle management server (in this case BOS)
  2. Dispatching server (in this case Sprinter)
  3. DZC server (accounting center) for single-use tickets
  4. Connection search engine server – simplifies ticket price determination by long distance queries
  5. Public internet connection:

a)       On-line payments to a bank server via transactions.

b)      Other servers (e.g. vehicle supervision, external management of adds in LCD, etc.)

Shared vehicle communication

Shared vehicle communication is characterized by utilizing a central communication unit, i.e. independent systems that use a shared modem can be built in a vehicle.

  • Each system in a vehicle can communicate with “its” server independently. All units have the same access to the communication unit.
  • Each system has to behave in a “secure” way. Each system has to be “unassailable“ because each system communicates via the internal Ethernet network.
  • If the communication unit can connect more ETH networks system security can be increased.
Shared vehicle communication

Shared vehicle communication

  • One data device
  • Secure separation of networks
  • Remote data management
  • Multiple-user system
  • Supports GPS and V2X
Shared vehicle communication – communication unit.

Shared vehicle communication – communication unit.

Managed island systems

In this case a vehicle contains a number of systems. Each of the systems has its own SIM card and uses it to communicate to its own server. In some cases using multiple SIM cards is better because of high traffic while:

  • There are multiple devices (systems) communicating out of the vehicle – island systems.
  • These systems are synchronized by an on-board computer.
  • Each system takes care of its security independently of the central one. It is necessary to ensure that an attacker cannot use these systems to get to the vehicle network.
Managed island systems.

Managed island systems.

Example of a combined arrangement

example of a combined arrangement.

example of a combined arrangement.

Unmanaged island system

There are multiple completely independent systems in a vehicle (control, information, passenger counting, checking, camera, ….). Each of them has its own control or supervision server.

  • There are independent systems in a vehicle, i.e. each supplier of “some” vehicle system is independent of the others including communication.
  • If one system is damaged the other systems are not affected (however it can happen that it does not provide information needed for operation)
  • System synchronization happens on the level of IT systems of the transportation company.
  • Each “island” takes care of its system security.

Such a system requires complicated coordination by the transportation company.

Example of how individual servers provide information to the dispatching and how data is assessed there – e.g. a comparison of the number of paying passengers to the number of passengers provided by the passenger counting system.

The information system obtains drive data from the dispatching and sends it to the unit in the vehicle.

Voice communication is managed by an SIP dashboard and the dispatching system sends communication parameters to it.

Unmanaged island systems.

Unmanaged island systems.

Vehicle communication via WiFi networks

WiFi communication is a medium-range high-speed communication acting as an alternative in depots or as a data source for passengers in vehicles. Currently, the most commonly used norm is  IEEE 802.a/c with communication speed of 430 MHz and higher.

Vehicle communication via WIFI networks.

Vehicle communication via WIFI networks.

  • Unwanted accesses to the company network through the depot WiFi have to be prevented
  • Multiple Wi-Fi with various SSID in one vehicle
  • Multiple Wi-Fi with various SSID in depots
  • High communication speed is needed in depots for the following reasons:
  • downloads of data from camera systems,
  • uploads of advertisement spots,
  • databases and checking,
  • maps, etc.

Communication via V2X

Contributions of the new technology to the security and efficiency of public transportation

  • Immediate information about vehicles in the surrounding area
  • Warnings about emergency situations – e.g. black ice, sudden deceleration
  • Electronic traffic signs – e.g. a temporary speed limit in a given area
  • Text information to vehicles
  • Displaying an intersection controller signal plan in a vehicle
  • Vehicle preference at intersections (e.g. public transportation, firefighters)
Communication via V2X

Communication via V2X

What is V2X (C2X)

  • Vehicle-to-Everything“ or „Car-to-everything“
  • Simple and regular communication among vehicles and among vehicles and transportation infrastructure (SSZ, RSU, stops)
  • Designed for all vehicles including public transportation

Communication via V2X

  • Modified Wi-Fi technology – 5.9 GHz (for Europe) – works on a reserved band for traffic – has a number of communication channels
  • Range – given by frequency and limited performance – in reality about 200 m up to 300 m in a city, and at direct visibility up to 1500 m
  • Ad-Hoc networks – random access networks where communication reliability is ensured by frequent message repetition
  • Europe wide standard – standardization (mostly finished) is underway on the level of application protocols – it is finished on the physical and the connection level
  • Certificate based authorization – messages sent by a vehicle must be digitally “signed” i.e. The sender and their rights must be clearly defined
  • GNSS – the system has to know its position to announce it to its surroundings of up to 100 ms.
What is V2X (C2X).

What is V2X (C2X)

Public transportation preference – V2X

In our system, it is used for direct and independent communication with intersections. Its range is about 300 m, in open terrain even over 1 km. A vehicle broadcasts information about its state (position, speed) periodically up to ten times a second.

At chosen points, this information is doubled by LTE which ensures that the information is delivered even in a difficult terrain. The earliest delivery is the valid one.

Public transportation preference – V2X

Public transportation preference – V2X

What a PT vehicle sees when using V2X

Bidirectional communication – vehicle requests, intersection controller replies and informs about the state.

Operation kinds:

  •   in Brno – one-way communication – production operation at 90 intersection and in 750  PT vehicles (delivery display by OC)
  •   in Ostrava – a short-term test, including „controlled stationing“ and displaying by OC – stop/go.
  •    Always fully replaces the previous radio communication without changing the controller unit
What a PT vehicle sees when using V2X

What a PT vehicle sees when using V2X

Practical results of using V2X

In more than 1,5 year of the duration of one of the biggest projects of PT preference in DPMB plc., it exceptional operation reliability has been proven.

Practical results of using V2X

Practical results of using V2X

Further development of applications directed towards ES in combination is possible.

Further system development directed towards tram collision prevention is possible.

Possibility of using external applications.

Possibility of using so called “controlled stationing”.

Possibility of a smooth transition from standard radio control to a V2X system.

Example of a tram state display related to the state of surrounding vehicles as shown on a tablet running our application.

Example of a tram state display related to the state of surrounding vehicles as shown on a tablet running our application.


This article is dealing with various vehicle communication solutions from the point of view of its inner busbar arrangement and arrangement of supervision servers in transportation companies or regional transportation coordinators.

The chosen solution depends on:

  • the required system functions and the amount of transferred data,
  • the possible component arrangement as per the system suppliers,
  • historical development in the transportation company (affects replacement costs),
  • the required system security.

The owner of the vehicle has to decide which arrangement is the best to meet their requirements. Most of the arrangements described above exist and are in operation.

When communication systems are installed in a vehicle, attention has to be paid to security and antenna placement to prevent interference.