Glossary Of Terms - Promax DT-800 Manual

CONTROL MODULE. DT-800

6. GLOSSARY OF TERMS

MODULATOR: In telecommunications, the modulation is the process of varying a
periodic waveform, i.e. a tone, in order to use that signal to convey
a message. Normally a high-frequency sinusoid waveform is used
as carrier signal. The three key parameters of a sine wave are its
amplitude ("volume"), its phase ("timing") and its frequency ("pitch"),
all of which can be modified in accordance with a low frequency
information signal to obtain the modulated signal. A device that
performs modulation is known as a modulator and a device that
performs the inverse operation of modulation is known as a
demodulator (sometimes detector or demod). A device that can do
both operations is a modem (short for "Modulator-Demodulator").
QPSK: Phase-shift keying (PSK) is a digital modulation scheme that
conveys data by changing, or modulating, the phase of a reference
signal (the carrier wave). Any digital modulation scheme uses a
finite number of distinct signals to represent digital data. PSK uses
a finite number of phases, each assigned a unique pattern of binary
bits. Usually, each phase encodes an equal number of bits. Each
pattern of bits forms the symbol that is represented by the particular
phase. The demodulator, which is designed specifically for the
symbol-set used by the modulator, determines the phase of the
received signal and maps it back to the symbol it represents, thus
recovering the original data. This requires the receiver to be able to
compare the phase of the received signal to a reference signal –
such a system is termed coherent (and referred to as CPSK).
Depending on the number of possible phases to take, are given
different names. The most common is to codify a number of bits per
symbol, then the number of phases to take is equal to an number
which is a power of two. In the case of QPSK (Quadrature Phase-
Shift Keying), uses four phases, displaced each other 90 degrees.
Normally are used as a phase jumping values 45 degrees, 135
degrees, 225 degrees and 315 º. Each symbol gives 2 bits. The
constellation diagram shows 4 symbols equally distributed.
MULTIPLEXER: In the field of telecommunications, the multiplexer is a device that
can receive and transmit multiple inputs by a shared transmission
medium. To do this it divides the transmission medium into multiple
channels, so that several nodes can communicate simultaneously.
A signal that is multiplexed must be de-multiplexed at the other end.
There are several types of multiplexing depending on how it is
performed this division of the transmission medium: frequency
division multiplexing, time division multiplexing, code division
multiplexing and wavelength division multiplexing.
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