Tutorial on TETRA Radio System Basics

This TETRA Radio System tutorial covers Trunk radio communication system or trunking radio basics. It mentions what is TETRA, TETRA interfaces, TETRA frequency bands, TETRA frame structure and TETRA standard references.

What is TETRA

TETRA is the short form of Trans-European Trunked Radio System. It is digital private mobile radio standard defined by ETSI.

TETRA mobile user can communicate to other users via base station or directly. TETRA user can be assigned one time slot or 4 time slots as transmission bandwidth. These 4 channels can be modulated over one RF carrier frequency. All the carriers are of 25KHz Bandwidth.

As the major application of TETRA trunk radio system is public safety as well as emergency services; call set up time should be less. Hence TETRA radio is designed to provide set up time of about 300ms. TETRA radio system supports semi duplex operations for group communication. It supports duplex operation for individual telephone calls. TETRA radio uses π/4 DQPSK modulation scheme. It has maximum transmission rate of about 36 Kbps. As mentioned RF carrier spacing is about 25KHz. RF frequency duplex spacing is 10MHz (45MHz is in 900 MHz frequency band). The TETRA frequency bands are mentioned below.

TETRA Network Interfaces

TETRA network interfaces

The fig-1 mentions the various TETRA network interfaces. As shown TETRA network consists of Air interface, Terminal Equipment Interface (TEI), Direct Mode Operation(DMO) and Inter-System Interface (ISI).

1. Air Interface ensures the interoperability of terminal equipment from different manufacturers.
2. TEI facilitates the independent development of mobile data applications.
3. ISI allows the interconnection of TETRA networks from different manufacturers.
4. DM0 guarantees communication between terminals also beyond network coverage.

TETRA Frequency bands

TETRA Voice+Data works on VHF of 150MHz and UHF of 900MHz frequency bands. The other TETRA frequency bands have following frequency values.
•  410MHz-420MHz, 420MHz-430MHz
•  450MHz-460MHz, 460MHz-470MHz
•  870MHz-888MHz, 915MHz-993MHz

TETRA Frame Structure

TETRA frame structure

The fig-2 depicts the TETRA frame structure. As mentioned TETRA frame is basically TDMA frame. Each frame composed of 4 time slots. About 18 such TDMA frames form one multi-frame. Total 17 frames are used for carrying information data and 1 frame (i.e. 18th frame) is used as control frame. This 18th channel is used as SACCH (i.e. Slow Associated Control Channel) to carry control channel signalling. The 60 such multi-frames will make 1 hyperframe of this TETRA Radio System or Trunk radio communication system. As mentioned time slot is the lowest unit of allocation which is made of 510 modulating bits.

1 TETRA Time Slot duration = 14.167 ms
1 TETRA frame duration = 56.67 ms
1 TETRA multi-frame= 1.02 second
1 TETRA hyperframe = 61.2 second

Similar to GSM slot, TETRA slot structures are of 3 types viz. uplink half slot, uplink full slot and downlink full slot. This slot structures carry five different types of physical bursts. These different bursts are transmitted over TETRA air interface as outlined above.

• Normal Downlink(Half time slots for random and reserved access)
• Synchronization Downlink(Full Slot used by mobile stations after the initial entry to the system)
• Control Uplink
• Normal Uplink
• Linearization Uplink

TETRA Standard References

Following table lists out ETSI references to TETRA standards for various applications.

TETRA Voice Plus Data ETS 300.392
Part 1 General Network Design
Part 2 Air interface
Part 3 Inner Working
Part 4 Gateways
Part 5 Terminal Equipment Interface
Part 6 Line Connected Stations
Part 7 Security
Part 8 Network Management Services
Part 9 Performance Objectives
Part 10 Supplementary Services Stage 1
Part 11 Supplementary Services Stage 2
Part 12 Supplementary Services Stage 3
Part 13 SDL Model for Air interface
Part 14 PICS

TETRA Packet Data Optimized(PDO) ETS 300.393
Part 1 General Network Design
Part 2 TETRA Air interface
Part 3 Inter working
Part 4 Gateways
Part 5 Terminal Equipment Interface
Part 6 Line connected stations
Part 7 security
Part 8 network management services
Part 9 performance objectives
Part 10 SDL model for air interface
Part 11 PICS performa

Part 1 General speech function description
Part 2 Codec
Part 3 specific operational features
Part 4 Codec conformance testing

TETRA Direct Mode Operation(DMO) ETS 300.396
Part 1 General network design
Part 2 Direct MS to MS radio interface
Part 3 Repeater
Part 4 Gateway
Part 5 Security

Difference between TETRA and TETRA2

Difference between TETRA and TETRA2 system

Other Digital Radio and Analog Radio Systems

TETRA Radio System
Difference between TETRA and TETRA2 system
APCO-25 versus APCO-16
Opensky Radio System
DMR-Digital Mobile Radio
iDEN-Integrate Digital Enhanced Network

Useful frame structures

16d 16e WiMAX Frame Structure  Zigbee frame  GPS Frame Structure  LTE Frame Structure  UMTS Frame Structure  SDH Frame Structure  802.11ac PHY Frame Structure  WLAN Frame  GSM Frame

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