Chapter 3 Overview; General; Digital Modulation Technology - Motorola MTP810 EX Basic Service Manual

OVERVIEW

General

To achieve a high spectrum efficiency, the MTP810 Ex 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 radio.
The process is called digital modulation.

Digital Modulation Technology

The MTP810 Ex is a TETRA ATEX Portable Radio that can operate in dispatch
and phone modes. The radio can also operate in TMO (Trunked Mode
Operation) and DMO (Direct Mode Operation) modes. It uses two digital
technologies:
π/4DQPSK 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 system can accommodate 4-voice channels in the standard 25 kHz channel
as used in the two-way radio.
Time Division Multiple Access (TDMA) is used to allocate portions of the RF
signal by dividing time into four slots, one for each radio.
Time allocation enables each radio to transmit its voice information without
interference from other transmitting units. Transmission from a radio 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
compressions/decompressions and RF modulation/demodulation.
π/4 DQPSK and Time Division Multiple Access (TDMA).
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CHAPTER 3
OVERVIEW