Matakuliah : H0484/Jaringan Komputer
Tahun
: 2007
Teknik Modulasi
Pertemuan 07
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan teknik modulasi
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Outline Materi
• Teknik Modulasi
• Modulasi analog
• Modulasi digital
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Encoding Techniques
• Analog data, carrier analog signal
• Digital data, carrier analog signal
Analog Modulation
• Analog data, carrier digital signal
Digital Modulation
• Digital data, carrier digital signal
Encoding
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Analog Data, Analog Signals
• Why modulate analog signals?
– Higher frequency can give more efficient
transmission
– Permits frequency division multiplexing
• Types of modulation
– Amplitude
– Frequency
– Phase
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Analog Modulation
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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
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LST/FASKD/CINQ
Type Modulasi Digital /Analog
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Modulation Techniques
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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 ASK
• Up to 1200bps on voice grade lines
• High frequency radio
• Even higher frequency on LANs using coax
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Phase Shift Keying
• Phase of carrier signal is shifted to represent data
• Binary PSK
– Two phases represent two binary digits
• Differential PSK
– Phase shifted relative to previous transmission
rather than some reference signal
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Quadrature PSK
• More efficient use by each signal element
representing more than one bit
– e.g. shifts of /2 (90o)
– Each element represents two bits
– Can use 8 phase angles and have more than
one amplitude
– 9600bps modem use 12 angles , four of which
have two amplitude
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4-PSK Constellation
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Quadrature Amplitude Modulation
• QAM used on asymmetric digital subscriber line (ADSL)
and some wireless
• Combination of ASK and PSK
• Logical extension of QPSK
• Send two different signals simultaneously on same
carrier frequency
– Use two copies of carrier, one shifted 90°
– Each carrier is ASK modulated
– Two independent signals over same medium
– Demodulate and combine for original binary output
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4-QAM and 8-QAM
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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.
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Pulse Code Modulation (PCM)
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