Matakuliah
Tahun
Versi
: H0174/Jaringan Komputer
: 2006
: 1/0
Pertemuan 07
Teknik Modulasi
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu:
• Menjelaskan teknik modulasi
2
Outline Materi
• Teknik Modulasi
• Modulasi analog
• Modulasi digital
3
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
4
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
5
Analog Modulation
6
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
7
LST/FASKD/CINQ
Type Modulasi Digital /Analog
8
Modulation Techniques
9
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
10
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
11
PSK Constellation
12
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
13
4-PSK Constellation
14
4-QAM and 8-QAM
15
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
16
BIT dan BAUD
17
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
Quadbit
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
8N18
ASK, FSK, 2-PSK
Matakuliah
Tahun
Versi
: H0174/Jaringan Komputer
: 2006
: 1/0
Pertemuan 08
Teknik Encoding
19
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan teknik encoding
20
Outline Materi
• Polar
• Bipolar
• Unipolar
21
Digital to Digital Encoding
22
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
23
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
24
Digital to Digital Encoding
25
Polar Encoding
26
Bipolar Encoding
27
Modulation Rate
28
Unipolar Encoding - NRZL
29
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
30
NRZ-L and NRZ-I
31
RZ Encoding
32
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
33
Manchester and Diff. Manchester
34
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
35
Bipolar AMI Encoding
36
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
37