Motorola MTM800 FuG ET, Базовое руководство по обслуживанию

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Overview 3 - 1
CHAPTER 3
OVERVIEW
General
The MTM5400/MTM800 FuG with Enhanced Control Head is Motorola’s latest and most advanced
digital mobile TETRA terminal. This terminal generation is based on a new digital platform
technology which takes care of the linear modulation type of terminals to support the TETRA needs.
It covers Trunk Mode Operation (TMO) as well as Direct Mode Operation (DMO) and among other
new features it is supplied with extended code and operating memory capacity to support all new
market requirements. The MTM5400/MTM800 FuG with Enhanced Control Head TETRA terminal
ensures a high audio quality.
To achieve high spectrum efficiency, the MTM5400/MTM800 FuG with Enhanced Control Head
uses digital modulation technology and sophisticated voice-compression algorithm. The voice of the
person speaking into the microphone is converted into a digital bit stream consisting of zeros (0) and
ones (1). This stream is then modulated into a radio-frequency (RF) signal, which is transmitted over
the air to another MTM5400/MTM800 FuG with Enhanced Control Head. The process is called
digital modulation.
Digital Modulation Technique
The MTM5400/MTM800 FuG with Enhanced Control Head is a 380–430 MHz mobile that can
operate in dispatch mode. It uses several digital technologies for voice and data transmissions.
Voice transmission
Voice transmission is performed using
π
/4 DQPSK and Time Division Multiple Access (TDMA).
π
/4 DQPSK is a modulation technique that transmits information by altering the phase of the radio
frequency (RF) signal. Data is converted into complex symbols, which alter the RF signal and
transmit the information. When the signal is received, the change in phase is converted back into
symbols and then into the original data.
The TETRA system can accommodate 4-voice channels in the standard 25 kHz channel as used in
the two-way terminal.
Time Division Multiple Access (TDMA) is used to allocate portions of the RF signal by dividing time
into four slots, one for each unit.
Time allocation enables each unit to transmit its voice information without interference from other
transmitting units. Transmission from a unit or base station is accommodated in time-slot lengths of
15 milliseconds and frame lengths of 60 milliseconds. The TDMA technique requires sophisticated
algorithms and a digital signal processor (DSP) to perform voice compression/decompression and
RF modulation/demodulation.