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TETRA |
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TETRA
Terrestrial Trunked Radio |
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Overview
TETRA is a TDMA standard, similar to the GSM standard. It uses four timeslots per carrier, the carrier bandwidth is 25 kHz. Similar to GSM, the first timeslot on the first carrier transmits the BCCH, a logical channel that bears synchronisation and control data.
The connection between mobile radio and base station is separated into two bands for uplink and downlink (frequency division duplex).
TETRA uses π/4 DQPSK (Differential Quaternary Phase Shift Keying). This modulation is highly efficient with spectrum resources, but requires high linearity of all RF components, especially the RF power amplifiers in the radios.
The TETRA services are based on three major service classes with different air interfaces, all specified by ETSI: |
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Voice plus Data (V+D), circuit switched speech and data transmission, (ETS 300 392)
Packet Data Optimized (PDO), data traffic based on packet switching, (ETS 300 393)
Direct Mode (DMO), a simplex voice transmission between two mobiles without using a network. On a physical channel two simultaneous DMO calls can be established. (ETS 300 396) |
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| Specifications |
| Frequency bands |
Assignment according to ETSI TS 100392-15 |
| TETRA can be used on all frequencies below 1000 MHz; frequency bands for Private Mobile Radio (PMR) and public safety applications are assigned on a national basis. |
870 to 876 MHz (UL), 915 to 921 MHz (DL)
380 to 390 MHz (UL), 390 to 400 MHz (DL)
410 to 420 MHz (UL), 420 to 430 MHz (DL)
450 to 460 MHz (UL), 460 to 470 MHz (DL) |
| Channel spacing |
25 kHz |
| Modulation |
π/4 DQPSK (Differential Quaternary Phase Shift Keying, phase shifts of π/4) |
| Modulation rate |
36 kbit/s |
| Bits per symbol |
2 |
| Access format |
TDMA (time-division multiple access)
TDD/FDD (time and frequency division duplex) |
| Number of channels per carrier |
4 time slots per TDMA frame (56.67 ms)
14.167 ms per time slot containing 255 symbols, BCCH in time slot 1 |
| MS power control |
Yes, in 5 dB steps from 15 dBm to 45 dBm |
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