Analog data, carrier analog signalDigital data, carrier analog
signal
Analog Modulation
Analog data, carrier digital signal
Digital Modulation
Digital data, carrier digital signal
Encoding
Analog Data, Analog Signals
Why modulate analog signals?Higher frequency can give more
efficient transmissionPermits frequency division multiplexing Types
of modulationAmplitudeFrequencyPhase
Analog Modulation
Modulasi
Tujuan:
Mengubah sinyal komputer yang digital menjadi sinyal analog yang
diperlukan oleh saluran komunikasi.Memperbesar jarak jangkau sinyal
informasi. Modem merupakan perangkat keras untuk kedua proses ini
LST/FASKD/CINQ
Type Modulasi Digital /Analog
Modulation Techniques
Frequency Shift Keying
Most common form is binary FSK (BFSK)Two binary values represented
by two different frequencies (near carrier)Less susceptible to
error than ASKUp to 1200bps on voice grade linesHigh frequency
radioEven higher frequency on LANs using coax
Phase Shift Keying
Phase of carrier signal is shifted to represent dataBinary PSKTwo
phases represent two binary digitsDifferential PSKPhase shifted
relative to previous transmission rather than some reference
signal
Quadrature PSK
More efficient use by each signal element representing more than
one bite.g. shifts of /2 (90o)Each element represents two bitsCan
use 8 phase angles and have more than one amplitude9600bps modem
use 12 angles , four of which have two amplitude
4-PSK Constellation
Quadrature Amplitude Modulation
QAM used on asymmetric digital subscriber line (ADSL) and some
wirelessCombination of ASK and PSKLogical extension of QPSKSend two
different signals simultaneously on same carrier frequencyUse two
copies of carrier, one shifted 90Each carrier is ASK modulatedTwo
independent signals over same mediumDemodulate and combine for
original binary output
4-QAM and 8-QAM
PULSE AMPLITUDE MODULATION
Pulse amplitude modulation has some applications, but it is not
used by itself in data communication. However, it is the first step
in another very popular conversion method called
pulse code modulation.
