Digital transmission systems :

The Tetra system:

All-digital communications mark a decisive step forward for Private Mobile Communications. Digital technology vastly improves the quality and security of communications while enabling greater volumes of information to be carried. Above all, digital technology means that systems can integrate a powerful encryption; transport high data rate, and shared, creating a radical change in comparison with the analogical radio market. To be powerful, Digital systems uses data codes correctors to prevent the loss of data packet.
Most digital communications systems using standard Tetra:

TETRA is a standard similar to the GSM standard. Like the GSM standard, the system  use a BCCH, a logical channel that provides timing and control data. The connection between the mobile radio station and the base station is split into two bands for uplinks and downlinks (Half-Duplex system).

TETRA uses the modulation π / 4 DQPSK.

 

There are many application using digital modulations:

1. The GSM
2. The Wi-Fi
3. Data link between radios systems
4. ACROPOL for the Police and ANTARES for the firefighters (not yet everywhere implemented in France.)

Here are the main advantages and disadvantages of digital communications systems:

Advantages:

• Communications are encrypted
• Radios are maller like GSM
• The radios can be tracked directly by GPS
• The connection between computer systems and radio system is more flexible.
• Some radios include a GSM module that allows calling directly on the conventional telephone network.

Disadvantages:

• It is a system "all or anything"
• The signal is too poor in some regions
• The system is sometimes complicated to use.

ACROPOL and ANTARES use Tetrapol. This is the same system as tetra except that the encryption and the algorithm are more powerful.
Tetra uses the band of 428 MHz and Tetrapol the band of the 380MHz.
This system, very expensive, is more difficult to deploy because it requires the implantation of several radio repeaters to cover an entire department.
It is impossible to intercept conversations using tetra because if you want to hear something, you must register the radio on the network.

Tetra systems use the same architecture that the GSM network:

These networks include mobile stations (radio), BTS (Base Transceiver Station) and an authentication server.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The software is used for the management, programming and radio tracking.
It lets you view the position of radios on a map in real time.