Tetrapol
Tetrapol is a digital, cellular trunked radio system for voice and data transmission that is specially tailored to the field of public safety. Trunked radio systems are professional radio systems for closed user groups such as private commercial radio applications or radio from authorities and organizations with security tasks (BOS). In contrast to other corporate radio systems, where the available transmission channels are only available to a permanently assigned user group, with trunked radio all available channels are distributed to the different groups as required. This increases the total number of possible users. The radius of a Tetrapol cell is up to 28 kilometers.
development
Tetrapol was originally developed by Matra and the European aerospace company EADS for the French security forces. One of the first users was the French gendarmerie , where Tetrapol has been used successfully since 1988. There are now 80 Tetrapol networks in 34 countries. EADS is still the only manufacturer of the Tetrapol technology and has already started to establish Tetrapol as the industry standard with the help of an association that was specifically initiated for this purpose.
Areas of application
In contrast to public mobile communications such as GSM , the use of trunked radio is restricted to a certain region. There is no provision for a so-called handover - i.e. passing on from cell to cell during a call.
Tetrapol is tailor-made for all areas of public safety such as the German Armed Forces , primarily because of service options such as group calls or the possibility that two or more mobile stations can communicate directly with each other without an intermediate base station. As if from the office, the emergency services can access information systems and databases with Tetrapol and query information: maps, site plans, information about chemical products or water protection areas, capacities of the surrounding hospitals or the locations of certain special vehicles in the region. With the help of digital radio, this information is transmitted securely to the respective emergency services via voice or data transmission.
The Tetrapol technology can also be installed as a company radio network. With such radio communication systems, employees from the areas of plant security, fire brigade , maintenance or from the high-bay warehouse can be connected to one another via digital radio. Previously, employees had to struggle through a whole range of different notification systems.
Nevertheless, the groups within a Tetrapol network work completely independently of one another. Switching from one group to the other is possible in the digital system without any major inconvenience. To do this, the system administrator only has to "activate" the desired group access. This is usually done when setting up the system. This fact is perceived by the users as very beneficial: not everyone has to listen to everything with the system, but can dial into the respective group radio networks that are relevant to them.
functionality
In contrast to the previous analog fixed-channel systems, in which each service or user was permanently assigned a specific radio channel, in trunked radio systems the frequencies are dynamically assigned to the individual subscribers and services. This makes use of the so-called bundle gain and often increases the spectrum efficiency many times over, depending on the type of use. The Tetrapol developers chose frequency division multiplexing (FDM or FDMA) as the channel access method . FDMA is the classic channel access method in which each user is assigned a specific frequency for a connection. This allows sending and receiving at the same time. With this method - all other things being equal - a greater range and thus better coverage of large areas is achieved than with other channel access methods (e.g. TDMA). At the same time, the base station continuously sends a control signal to each radio cell. On this control channel, the base station continuously supplies the connected mobile devices with the latest system data from the network. Tetrapol can basically be used on frequencies between 70 and 520 MHz. In practice, however, only the typical frequencies designated for PMR in the 80 , 160 and 400 MHz bands are used . As with most radio systems, Tetrapol also uses the frequency duplex method. The uplink and the downlink are handled on two different frequencies, which are distinguished from each other by the so-called duplex spacing.
compatibility
Due to the proprietary radio standard, there is no compatibility with other radio systems. Tetrapol works with FDMA , while TETRA works with TDMA . Interaction via the air interface is impossible.
Telephone services
- Individual Call: This service corresponds to the connection in a public mobile radio system (GSM, UMTS). A participant calls a certain other participant and is connected to this.
- Group Call: A participant calls a predetermined group. Every member of the group can overhear everything and also speak. A group can be modified dynamically, so members can be added or removed.
- Direct mode: In direct mode, two or more mobile stations communicate directly with one another without involving a base station. This can be used in places where there is no radio coverage - for example in a tunnel or the basement of a building.
- Broadcast Call: This is a unidirectional point-to-multipoint connection in a specific area. The area and the participants are determined in advance. The individual participants do not acknowledge the call and consequently the caller cannot control who has received the call or not.
- Emergency Call: An emergency call button can be used to establish a connection with high priority to a dispatcher or a predetermined group of participants.
- Include Call: This call allows one or more additional participants to be called during a conversation and included in the conversation.
- Open Channel: A group of participants can talk to each other on a specific channel for a specific time. Within the group everyone hears everyone else and can speak at any time. To take part in the conversation, the participant only needs to enter the number of the "Talk group". The numbers of the “talk groups” active at a certain time are sent out on the control channel and are known to all participants in the network.
Data services
- Paging: Short messages can be sent to the mobile station by a dispatcher.
- Status transmission: Very short, predefined messages can be transmitted from the dispatcher to the mobile stations and vice versa, or between the mobile stations.
- Short Data Messaging: This data service allows participants to exchange short messages very quickly.
- X.25 Packet Data Services: This data service enables an X.25 connection to be established between two end devices.
- TCP / IP Access: This data service allows mobile stations to access the Internet or servers that support the TCP / IP protocol.
See also
Web links
- Tetrapol portal
- Page no longer available , search in web archives: fact sheet of the Swiss Federal Office for Communication with a comparison to TETRA