Komunikasi Data (TEU...
37
Komunikasi Data (TEU 611) Digital Transmission Dr. I Wayan Mustika, ST., M.Eng. Jurusan Teknik Elektro dan Teknologi Informasi FT UGM
Transcript of Komunikasi Data (TEU...
Komunikasi Data (TEU 611)
Digital Transmission
Dr. I Wayan Mustika, ST., M.Eng.
Jurusan Teknik Elektro dan Teknologi Informasi FT UGM
Outline
Ø Digital-to-Digital Conversion Ø Line Coding Ø Block Coding Ø Scrambling
Ø Analog-to-Digital Conversion Ø Pulse Code Modulation (PCM) Ø Delta Modulation (DM)
Ø Transmission Modes Ø Parallel Transmission Ø Serial Transmission
Line Coding and Decoding
§ Line coding converts a sequence of bits to a digital signal
Signal Element vs. Data Element
Example
§ A signal is carrying data in which one data element is encoded as one signal element (r = 1). If the bit rate is 100 kbps, what is the average value of the baud rate if c is between 0 and 1?
Solution We assume that the average value of c is 1/2. The baud rate is then
§ Baseline Wandering A long strings of 0s or 1s can cause a drift in a baseline and make it difficult for the receiver to decode correctly
§ DC Components When the voltage level in a digital signal is constant for a while, the frequency spectrum is around zero, called DC components
§ Self-synchronization If the receiver clock is faster or slower, the bit intervals are not matched and the receiver might misinterpret the signals
Amarudin
Note
Signal yang o atau 1, panjang sekali maka receiver akan sulit untuk mendeteksi, karena sulit mau dari mana memeulai dan selesai deteksi.
Amarudin
Note
Jika jam penerima lebih cepat atau lebih lambat, interval bit tidak cocok dan penerima mungkin salah menafsirkan sinyal
Effect of Lack of Synchronization
Line Coding Schemes
Unipolar NRZ
Amarudin
Note
NRZ (Non Return be Zero): tidak kembali jika zero. kelemahannya jika data diberikan berupa 0 terus atau 1 terus maka susah dalam sinkronisasi sampai mana batas bitnya.
Polar NRZ-L and NRZ-I Schemes
§ Two levels of voltage amplitude are used
Amarudin
Note
JIka mendapatkan data 0 maka tidak di invers(balik), namun jika ketemu data 1 maka di invers,ex: jika ada 0 ketemu 1 maka menjadi 0, jika ada 0 ketemu ketemu 0 maka tetap 0, jika ada 0 ketemu 1 maka menjadi 1.
Summary of NRZ-L and NRZ-I Schemes
§ In NRZ-L the level of the voltage determines the value of the bit. In NRZ-I the inversion or the lack of inversion determines the value of the bit
§ NRZ-L and NRZ-I both have an average signal rate of N/2 Baud
§ NRZ-L and NRZ-I both have a DC component problem
Amarudin
Note
N=data rate
Example
§ A system is using NRZ-I to transfer 10-Mbps data. What are the average signal rate and minimum bandwidth?
Solution The average signal rate is S = N/2 = 500 kbaud. The minimum bandwidth for this average baud rate is Bmin = S = 500 kHz.
Amarudin
Note
5000 kboud
Polar RZ Scheme
§ In RZ scheme, three values are used: positive, negative and zero.
Amarudin
Note
di pertenganhan bid maka berupah. ex: dari -1 setengah bit kemudian jadi 0. dari 0 setengah bit kemudian jadi 1. dari 1 setengah bit kemudian jadi 0. dari 0 setengah bit kemudian jadi -1. dst...
Polar Biphase: Manchester and Differential Manchester Schemes
Amarudin
Note
1 data dengan 2 elemen
Summary of Manchester and Differential Manchester
§ In Manchester and differential Manchester encoding, the transition at the middle of the bit is used for synchronization
§ The minimum bandwidth of Manchester and differential Manchester is 2 times than that of NRZ
Bipolar Schemes: AMI and Pseudoternary
Amarudin
Note
hanya perbedaan teknik saja, tidak lagi menggunakan aturan encoding manchester.
Amarudin
Note
JIka ada dua bit yang sama,maka aka di invers(dibalik), kelemahannya jika ada data 0 panjang maka susah disinkronisasikan, sehingga timbul arus DC, begitu pula jika ada data 1 panjang maka susah juga.
Multilevel Scheme (2B1Q)
Amarudin
Note
kelemahan berada pada receiver untuk mengenali 4 aturan tsb, sehingga pada receiver butuh tabel aturan juga.
Amarudin
Note
Previous Level
Block Coding
Using Block Coding 4B/5B with NRZ-I Line Coding Scheme
Scrambling: AMI used with scrambling
§ Can be used for long-distance communication
Two Cases of B8ZS Scrambling Technique
Analog-to-Digital Conversion
Ø Pulse Code Modulation Ø Delta Modulation
Amarudin
Note
ex: transfer lagu dari caset tape menjadi MP3
Pulse Code Modulation
Sampling Methods for PCM
Nyquist Sampling Rate for Low-pass and Bandpass signals
§ According to the Nyquist theorem, the sampling rate must be at least 2 times the highest frequency contained in the signal
Amarudin
Highlight
Amarudin
Note
Ex: biasanya utk MP3 secara prakteknya memiliki Sampling 44,1 kHz. dengan Frekuensi 20,05 kHz. namun secara teorinya memiliki Sampling 20 khz. dengan Frekuensi 20 kHz.
Recovery of a Sampled Sine Wave for Different Sampling Rates
Quantization and Encoding of a Sampled Signal
Example
§ We want to digitize the human voice. What is the bit rate, assuming 8 bits per sample?
Solution The human voice normally contains frequencies from 0 to 4000 Hz. So the sampling rate and bit rate are calculated as follows:
Amarudin
Highlight
Amarudin
Note
8 bits per sample
Components of a PCM decoder
The Process of Delta Modulation
Delta modulation and demodulation components
Transmission Modes
Parallel Transmission
Serial Transmission
Asynchronous Transmission
Synchronous Transmission
Amarudin
Note
MATERI FISIK LAYER SUDAH SELESAI SAMPAI DISINI
Assignment 2
1. What is the Nyquist sampling rate for each of the following signals? a. A low-pass signal with bandwidth of 200 KHz? b. A band-pass signal with bandwidth of 200 KHz if the lowest
frequency is 100 KHz? 2. We have sampled a low-pass signal with a bandwidth of
200 KHz using 1024 levels of quantization. a. Calculate the bit rate of the digitized signal. b. Calculate the SNRdB for this signal. c. Calculate the PCM bandwidth of this signal.
