CPET/ECET 355 4. Digital Transmission Data Communications and Networking Fall 2004 Professor Paul I-Hai Lin Electrical and Computer Engineering Technology Indiana University-Purdue University Fort Wayne www.ecet.ipfw.edu/~lin 4. Digital Transmisison - Lin
4.1 Line Encoding • A process converting binary data, a sequence of bits, to a digital signal • Binary data: data, text, numbers, graphical images, audio, and video • Some characteristics: Signal levels, bit rate, dc components, self-synchronization From p. 85, Figure 4.1 of Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • Signal Level vs. Data Level Three signal levels, 2 data levels From p. 86, Figure 4.2 of Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • Pulse Rate vs. Bit Rate • Pulse Rate • Number of pulses per second • A pulse is the min amount of time required to send a symbol • Bit Rate • Number of bits per second • BitRate = PulseRate x Log2L • Level of signal = 2, BitRate = PulseRate • Level of signal = 4, BitRate = 2 x PulseRate • Example 1 & 2: Find Bit rate • If - Pulse rate 1000 pulses/sec, L = 2, 1000 bps • If - Pulse rate 1000 pulses/sec, L = 4, 2000 bps 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • DC Components (undesirable) • Cannot passing through a transformer • Unnecessary energy on the line From p. 87, Figure 4.3 of Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • Self-Synchronization (desirable) • For correctly interpret signal • Sending 10110001; receiving 110111000011 Figure 4.4 Lack of Synchronization, From p. 88, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • Line Coding Schemes • Unipolar • Simple and primitive • One voltage level • Two problems: DC component & Lack of synchronization • Polar • Two signal levels: positive & negative • Eliminate DC component • Biploar • Three signal levels: positive, zero, and negative 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • Unipolar Encoding Figure 4.6 Unipolar Encoding, From p. 89, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • Polar Encoding • NRZ: Non Return to Zero • RZ: Return to Zero • Manchester • Differential Manchester 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • NRZ: Non Return to Zero • NRZ-L • 0 positive; 1 negative • Sync. Problem if long string of 0s or 1s is encountered • NRZ-I • the signal is inverted if a 1 is encountered • A long string of 0s still cause sync. problem Figure 4.8 NRZ-L and NRZ-I Encoding, From p. 91, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • RZ: Return to Zero • Uses three values: positive, zero, negative • Ensure Sync: a signal change for each bit • Main disadvantage: use more bandwidth Figure 4.9 RZ Encoding, From p. 91, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • Manchester Encoding • Uses two level signal values: positive, negative • Sync: Inversion at the middle of each bit • Zero: High -> Low; One: Low -> High Figure 4.10 Manchester Encoding, From p. 92, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • Differential Manchester Encoding • Uses two level signal values: positive, negative • Sync: Inversion at the middle of each bit • Zero: A transition; One: No transition Figure 4.10 Differential Manchester Encoding, From p. 93, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.1 Line Encoding (cont.) • Biploar Encoding • Uses three level signal values: positive, zero, negative • 0: Zero level; 1: Alternating positive and negative voltages • AMI: Alternate Mark Inversion • BnZS: Bipolar n-zero Substitution Figure 4.12 Bipolar AMI Encoding, From p. 94, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.2 Block Encoding • Improve performance • Ensure synchronization through redundancy bits • Block Encoding Schemes • 4B/5B: 4-bit data encoded into 5-bit code • 8B/10B: 8-bit data encoded into 10-bit code • 8b/6T: 8-bit data encoded into 6-symbol code 4. Digital Transmisison - Lin
4.2 Block Encoding (cont.) • Block Encoding Figure 4.15 Block Encoding, From p. 95, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.2 Block Encoding (cont.) • 4B/5B Block Substitution • Better Sync & Error detection • 16 groups -> 32 groups • No more than 3 consecutive 0s Figure 4.16 Substitution in Block Encoding, From p. 95, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.2 Block Encoding (cont.) • 4B/5B Encoding Table Table 4.1 4B/5B Encoding, From p. 97, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.2 Block Encoding (cont.) • 4B/5B Encoding Table Table 4.1 4B/5B Encoding, From p. 97, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.2 Block Encoding (cont.) • 8B/6T Encoding • 28: 256 possibilities • 36: 729 six-symbol ternary signal Figure 4.17 Example of 8B/6T Encoding, From p. 98, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.3 Sampling • Pulse Amplitude Modulation (PAM) • Sample & Hold circuit • Pulse Code Modulation (PCM) • Quantized PAM • Sampling Rate • Nyquist theorem • How many bit per sample 4. Digital Transmisison - Lin
4.3 Sampling (cont.) • PAM Figure 4.18 PAM, From p. 99, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.3 Sampling (cont.) • Quantized PAM Signal Figure 4.19 Quantized PAM Signal, From p. 100, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.3 Sampling (cont.) • Quantization, sign & magnitude Figure 4.20 Quantizing by using sign and magnitude, From p. 100, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.3 Sampling (cont.) • PCM Figure 4.21 PCM, From p. 101, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.3 Sampling (cont.) • PCM Figure 4.22 From analog signal to PCM digital code, From p. 101, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
= x Hz = 2 x samples 4.3 Sampling (cont.) • Nyquist Theorem • Sampling rate must be at least 2 times the highest frequency = ½ x Figure 4.23 Nyquist Theorem, From p. 102, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.3 Sampling (cont.) • Examples • Q1: What sampling rate is needed for a signal with a bandwidth of 10 KHz (1KHz to 11KHz) • A1: Sampling rate = 2 x 11 KHz = 22,000 samples per second 4. Digital Transmisison - Lin
4.3 Sampling (cont.) • Examples • Q2: A signal is sampled. Each sample requires at least 12 levels of precision (+0 to +5 and 0 to -5). How many bits should be sent for each sample? • A2: 4-bit • 1-bit for sign • 3-bit for magnitude (8-levels) 4. Digital Transmisison - Lin
4.3 Sampling (cont.) • Examples • Q3: We want to digitize the human voice. What is the bit rate, assuming 8-bits per sample? • A3: BW of Human voice 0-4000 Hz • Sampling rate 4000 x 2 = 8000 samples/sec • Bit rate • 8000 sample/sec x 8 bit/sample = 64,000 bps 4. Digital Transmisison - Lin
4.4 Transmission Mode • Parallel • Serial • Synchronous • Asynchronous Figure 4.25 Parallel transmission, From p. 104, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.4 Transmission Mode • Serial Transmission Figure 4.26 Serial transmission, From p. 105, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.4 Transmission Mode • Serial - Asynchronous Figure 4.27Asynchronlus transmission, From p. 106, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
4.4 Transmission Mode • Serial - Synchronous Figure 4.28 Synchronlus transmission, From p. 107, Data Communications and Networking, Forouzan, McGrawHill 4. Digital Transmisison - Lin
Summary Questions? 4. Digital Transmisison - Lin
