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Pertemuan 07Teknik Modulasi

Matakuliah : H0174/Jaringan Komputer

Tahun : 2006

Versi : 1/0

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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 signalDigital Modulation

• Digital data, carrier digital signalEncoding

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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

LST/FASKD/CINQ

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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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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 amplitudes

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4-PSK Constellation

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4-QAM and 8-QAM

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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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BIT dan BAUD

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ModulationModulation UnitsUnits Bits/BaudBits/Baud Baud rateBaud rate Bit Rate

ASK, FSK, 2-PSKASK, FSK, 2-PSK Bit 1 N N

4-PSK, 4-QAM4-PSK, 4-QAM Dibit 2 N 2N

8-PSK, 8-QAM8-PSK, 8-QAM Tribit 3 N 3N

16-QAM16-QAM Quadbit 4 N 4N

32-QAM32-QAM Pentabit 5 N 5N

64-QAM64-QAM Hexabit 6 N 6N

128-QAM128-QAM Septabit 7 N 7N

256-QAM256-QAM Octabit 8 N 8N

Perbandingan Bit dan Baud rate

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Pertemuan 08Teknik Encoding

Matakuliah : H0174/Jaringan Komputer

Tahun : 2006

Versi : 1/0

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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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Nonreturn to Zero Inverted

• Polar, Non Return To Zero Inverted• 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 (& thus data rate) lead to

higher costs– Some codes require signal rate greater than

data rate