Transmisi Pitadasar
Baseband Transmission
6
Sistem Komunikasi Digital Digital Communication
Dr. Eng. Wahyul Amien Syafei
Baseband Transmission
• To transmit information through physical
channels, PCM sequences (codewords) are transformed to pulses (waveforms).
– Each waveform carries a symbol from a set of size M.
– Each transmit symbol represents bits of the PCM words (l=log2{1/2p}).
– PCM waveforms (line codes) are used for binary symbols (M=2).
– M-ary pulse modulation are used for non-binary symbols (M>2).
PCM waveforms
PCM waveforms category:
3. Phase encoded
4. Multilevel binary
1. Nonreturn-to-zero (NRZ)
2. Return-to-zero (RZ)
1 0 1 1 0
0 T 2T 3T 4T 5T +V
-V +V 0 +V 0 -V
1 0 1 1 0
0 T 2T 3T 4T 5T +V
-V +V -V +V 0 -V NRZ-L
Unipolar-RZ
Bipolar-RZ
Manchester Miller
Dicode NRZ
Nonreturn to zero ( NRZ)
Digunakan di PCM.
3 tipe NRZ:
Nonreturn to zero ( NRZ)
1. NRZ–L (Level) digunakan dalam sirkit logika digital. Biner 1 dan 0 di representasikan dengan level tegangan yg
berbeda.
2. NRZ-M (Mark) digunakan pada magnetic tape recording.
Biner 1 dan 0 direpresentasikan dengan ada dan tidaknya perubahan level tegangan.
3 NRZ-S (Space) kebalikan dari NRZ-M. Biner 0 dan 1 direpresentasikan dengan ada dan tidaknya perubahan level tegangan.
Return to zero (RZ)
3 sub-grup:
Alternate Mark Inversion
Return to zero (RZ)
1. Unipolar RZ.
1. Biner 1: setengah lebar pulsa, 2. Biner 0: tidak ada pulsa .
2. Bipolar RZ. Biner 1 dan 0 direpresentasikan dengan Pulsa yang berbeda polaritas juga lebarnya setengah lebar pulsa.
3. RZ-AMI (Alternate Mark Inversion ) adalah skema signaling yang digunakan dalam sistem telepon.
1. Biner 1: alternative pulsa.
2. Biner 0: tidak ada pulsa
Phase encoded
1. Bi-Ø-L (bi-phase-level) or Manchester 2. Bi-Ø-M(bi-phase-mark).
3. Bi-Ø-S (bi-phase-space)
4. Delay modulation
Multilevel binary
Bentuk gelombang biner 3 level, Bipolar RZ dan RZ-AMI termasuk grup ini.
1. Dicode NRZ
2. Dicode RZ
PCM waveforms
• Criteria for comparing and selecting PCM waveforms:
– Spectral characteristics (power spectral density and bandwidth efficiency)
– Bit synchronization capability – Error detection capability
– Interference and noise immunity
– Implementation cost and complexity
Spectra of PCM waveforms
M-ary pulse modulation
• M-ary pulse modulations category:
• M-ary pulse-amplitude modulation (PAM)
• M-ary pulse-position modulation (PPM)
• M-ary pulse-duration modulation (PDM)
– M-ary PAM is a multi-level signaling where each
symbol takes one of the M allowable amplitude levels, each representing bits of PCM words.
– For a given data rate, M-ary PAM (M>2) requires less bandwidth than binary PCM.
– For a given average pulse power, binary PCM is easier to detect than M-ary PAM (M>2).
PCM signaling
Latihan
Informasi dlm bentuk analog dg fm=3kHz hendak ditransmisikan dg sistem 16-ary PAM. Distorsi kuantisasi (p) dibatasi 1% dari Vpp. Hitunglah:
a. jumlah bit/sample (PCM word (l))
b. fs minimal dan lajut bit (R) yg dihasilkan c. Laju symbol PAM (Rs)
d. Efisiensi bandwidth jika bandwidth transmisi
(W) (termasuk filtering) adl 12 kHz.
Solusi
a. l > log2 {1/2p}
b. R = l.fs
c. Rs = R/k = R/log2{M}
d. Efisiensi BW = R/W (bit/Hz)
HW – 6
• Do Exercises: 2.11 - 2.15
• Transmit your nick name using:
– NRZ – RZ
– Phase encoded – Multilevel Binary
• Analyze the curve and decide which code
you will use
