# 5 modulasi+encoding.

Teknik Modulasi
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 DARI KOMPUTER YANG DIGITAL
MENJADI SINYAL ANALOG YANG DIPERLUKAN OLEH
SALURAN KOMUNIKASI
• MEMPERPANJANG JARAK JANGKAU SINYAL INFORMASI
• MODEM MERUPAKAN HARDWARE UNTUK KEDUA
PROSES INI
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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 co-ax
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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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PSK Constellation
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• 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 amplitudes
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4-PSK Constellation
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4-QAM and 8-QAM
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• 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&deg;
– Each carrier is ASK modulated
– Two independent signals over same medium
– Demodulate and combine for original binary output
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BIT dan BAUD
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Perbandingan Bit dan Baud rate
Modulation
Units
Bits/Baud
Baud rate
Bit Rate
Bit
1
N
N
4-PSK, 4-QAM
Dibit
2
N
2N
8-PSK, 8-QAM
Tribit
3
N
3N
16-QAM
4
N
4N
32-QAM
Pentabit
5
N
5N
64-QAM
Hexabit
6
N
6N
128-QAM
Septabit
7
N
7N
256-QAM
Octabit
8
N
8N
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Teknik Encoding
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Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan teknik encoding
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Outline Materi
• Polar
• Bipolar
• Unipolar
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Digital to Digital Encoding
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Terminologi
• Unipolar
– All signal elements have same sign
• Polar
– One logic state represented by positive voltage the
other by negative voltage
• Data rate
– Rate of data transmission in bits per second
• Duration or length of a bit
– Time taken for transmitter to emit the bit
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Terminologi
• Modulation rate
– Rate at which the signal level changes
– Measured in baud = signal elements per second
• Mark and Space
– Binary 1 and Binary 0 respectively
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Digital to Digital Encoding
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Polar Encoding
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Bipolar Encoding
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Modulation Rate
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Unipolar Encoding - NRZL
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•
•
•
•
Non return to zero, inverted on ones
Constant voltage pulse for duration of bit
Data encoded as presence or absence of signal
transition at beginning of bit time
• Transition (low to high or high to low) denotes a
binary 1
• No transition denotes binary 0
• An example of differential encoding
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NRZ-L and NRZ-I
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RZ Encoding
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Biphase
• Manchester
– Transition in middle of each bit period
– Transition serves as clock and data
– Low to high represents one
– High to low represents zero
– Used by IEEE 802.3
• Differential Manchester
– Mid bit transition is clocking only
– Transition at start of a bit period represents zero
– No transition at start of a bit period represents one
– Used by IEEE 802.5
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Manchester and Diff. Manchester
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Multilevel Binary
• Use more than two levels
• Bipolar-AMI
– zero represented by no line signal
– one represented by positive or negative pulse
– one pulses alternate in polarity
– No loss of sync if a long string of ones (zeros still a
problem)
– No net dc component
– Lower bandwidth
– Easy error detection
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Bipolar AMI Encoding
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Perbandingan skema enkoding
• Error detection
– Can be built in to signal encoding
• Signal interference and noise immunity
– Some codes are better than others
• Cost and complexity
– Higher signal rate (&amp; thus data rate) lead to higher
costs
– Some codes require signal rate greater than data rate
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