Materi 2 - Transmisi Data

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26 gauge
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24 gauge
Attenuation (dB/mi)
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24
22 gauge
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18
19 gauge
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12
9
6
3
f (kHz)
1
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1000
Figure 3.37
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Received
Sent
•contoh. Transmisi AM, FM, TV
(b) Transmisi digital : hanya level diskrit yang perludireproduksi
Received
Sent
•contohtelepon digital, CD Audio
Copyright ©2000 The McGraw Hill Companies
Leon-Garcia & Widjaja: Communication Networks
Figure 3.6
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Analog versus Digital
DCC 6th Ed. W.Stallings
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Transmisi Analog
Source
Amplifier
Amplifier
Destination
Repeater
Destination
Transmisi Digital
Source
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Repeater
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Figure 3.7
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Transmisi Analog
Attenuated & distorted signal
+
noise
Amp.
Equalizer
Recovered signal
+
residual noise
Amplifier
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Leon-Garcia & Widjaja: Communication Networks
Figure 3.8
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Digital Transmission
Decision Circuit.
& Signal
Regenerator
Amplifier
Equalizer
Timing
Recover
y
Repeater (digital signal)
Copyright ©2000 The McGraw Hill Companies
Leon-Garcia & Widjaja: Communication Networks
Figure 3.9
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Sumber
informasi
Pengkode
Sumber
(source
encoder)
Pengkode
Saluran
(channel)
encoder)
Modulator
Digital
Saluran
Transmisi
Penguat
output
Decoder
Sumber
(source
decoder)
Decoder
Saluran
(channel)
decoder)
Demodulator
Digital
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SinyalMenempuhJarak
Sinyal Di
Ideal
Real
Penerima
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Interferensi Antar Simbol (ISI)
Misal ada dua path.
Path yang pendek mempunyai panjang d1,
path yang panjang mempunyai panjang d2.
Apa perbedaan delay propagasi antara
keduanya?
Simbol
diterima di
path pendek
Simbol
diterima di
path panjang
2
3

1
3
0
2
1
0
Berapa besar  agar 3 di path
panjang diterima tepat saat 0 di path
pendek diterima?
Berapa perbedaan panjang path agar
hal ini bisa terjadi?
Sinyal
diterima –
gabungan
kedua sinyal
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DCC 6th Ed. W.Stallings
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Laju data maks:: C = 2H log 2 (V)bit/detik.
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(a) Lowpassdankanallowpassideal
A(f)
A(f)
1
f
0
H
f
0
H
(b) Lajutransmisipulsamaksimumadalah2Hpulsa/detik
Kanal
t
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t
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Figure 3.11
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signal
signal + noise
noise
High
SNR
signal +
noise
noise
signal
t
t
t
Low
SNR
t
t
t
Average Signal Power
SNR =
Average Noise Power
SNR (dB) = 10 log10SNR
Copyright ©2000 The McGraw Hill Companies
Leon-Garcia & Widjaja: Communication Networks
Figure 3.12
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C = H log 2 (1 + SNR)
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Kegunaan:
1. Efesiensidaya
2. Memaksimalkan
bandwidth
3. Mengurangi
sampling error
Sistemharussepasa
ng
(samacodingnya
)
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Signal Constellations
Bk
Bk
Ak
Ak
4 “levels”/ pulse
2 bits / pulse
2D bits per second
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16 “levels”/ pulse
4 bits / pulse
4D bits per second
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Figure 3.34
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