Tips and best practices

Easy location updates

Tetrapol has a cool feature that helps set up location apps.


Thanks to a Tetrapol feature known as DDCH, dispatchers can keep track of field personnel with extra convenient location updates. This feature helps in two location apps:

  • Automatic Vehicle Location (AVL) lets dispatchers locate and track vehicles that have a GPS equipped mobile radio on board.
  • Automatic Terminal Location (or Automatic Person Location, APL) allows the dispatchers to track and trace personnel who carry a GPS-enabled handheld radio.

What is DDCH?

A Tetrapol feature known as DDCH lets radio terminals send regular updates to the network - efficiently, conveniently, and reliably.

In other words, radio terminals can exchange small data messages with the system while continuing with their current operations.

For these small data messages, the system uses a specific radio channel known as the Dedicated Data CHannel (DDCH). Short messages of nine bytes in length move on this channel, and it does not matter if the radio terminal is in communication or on the control channel.

Location apps in action

Let's say that a dispatcher wants to see the field personnel's locations on a map.

  • The people on foot move more slowly - their location does not have to be updated that often.
  • The vehicles move fast - their location should be updated more often.

The dispatchers can decide how often the location updates run. They can also change the update frequency for a vehicle in pursuit of a suspect, for example.

The staff only need to decide their priorities and requirements: together with the AVL solution, the Tetrapol DDCH feature will manage the location updates.

DDCH - how it works

The Tetrapol radio needs a GPS receiver: a connection to one or an embedded receiver.

The radio will automatically ask the AVL server for a data transmission configuration. This commits the radio terminal to communicate with the AVL server periodically, to transmit its position at certain intervals. For example, a pedestrian radio would update its location every four minutes and a vehicle radio every 30 seconds. When needed, the radio in a vehicle giving chase would update its position every few seconds.

The radio terminal requests that the network assigns a dedicated time slot in the DDCH for it. Using the time slot, the radio can decide to send its position on its own, without network intervention. This avoids the classic data exchange and handshaking that occur whenever a radio wants to send data to a server.

The network will dedicate a time slot for this terminal. It will choose an available time slot according to the update interval.

The network can support up to three DDCH per base station cell.

In this example:

  • The location of up to 300 vehicles and more than 800 pedestrians per DDCH per base station cell could be followed.
  • In addition, the location of a few pursuing vehicles could be followed.
  • Or, 1000 radios per DDCH per base station cell can be monitored if they send their location once per minute.
  • Or, 500 radios if they send their location every 30 seconds.

Efficient location updates

The data messaging related to AVL is extremely efficient thanks to the use of DDCH.

  • No need for the usual polling and data exchanges between the network and the radio
  • No risk of message collision or loss of messages when the radio tries to send its location on the fly.

Roaming - taken care of

When the radio roams to another base station cell, the network will automatically dedicate a new time slot from the new cell for the radio. No action from the radio user or control centre personnel is required.

If the new base station cell has no DDCH time slots left, the radio will ask the network to use the back-up data sending mode. In other words, the radio and the network exchange the standard data messages and handshakes. This is not as efficient as the use of DDCH but the location updates from the radio continue to arrive. 

Other applications

Using the DDCH does not limit to location updates. It can be used for every type of data. The example describes how DDCH works in an AVL scenario – monitoring the changing location of a radio. It could also be used for other applications, such as:

  • Following the water levels in a river
  • Monitoring a critical temperature in a plant
  • In any other critical sensor system that needs to be monitored.

Location apps and other data applications can really become easier thanks to Tetrapol’s DDCH feature.