1. 9/12/2004 4. Digital Transmisison - Lin 1 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

2. 9/12/2004 4. Digital Transmisison - Lin 2 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

3. 9/12/2004 4. Digital Transmisison - Lin 3 4.1 Line Encoding (cont.) Signal Level vs. Data Level From p. 86, Figure 4.2 of Data Communications and Networking, Forouzan, McGrawHill Three signal levels, 2 data levels

4. 9/12/2004 4. Digital Transmisison - Lin 4 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 Log 2 L –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

5. 9/12/2004 4. Digital Transmisison - Lin 5 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

6. 9/12/2004 4. Digital Transmisison - Lin 6 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

7. 9/12/2004 4. Digital Transmisison - Lin 7 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

8. 9/12/2004 4. Digital Transmisison - Lin 8 4.1 Line Encoding (cont.) Unipolar Encoding Figure 4.6 Unipolar Encoding, From p. 89, Data Communications and Networking, Forouzan, McGrawHill

9. 9/12/2004 4. Digital Transmisison - Lin 9 4.1 Line Encoding (cont.) Polar Encoding –NRZ: Non Return to Zero –RZ: Return to Zero –Manchester –Differential Manchester

10. 9/12/2004 4. Digital Transmisison - Lin 10 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

11. 9/12/2004 4. Digital Transmisison - Lin 11 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

12. 9/12/2004 4. Digital Transmisison - Lin 12 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

13. 9/12/2004 4. Digital Transmisison - Lin 13 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

14. 9/12/2004 4. Digital Transmisison - Lin 14 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

15. 9/12/2004 4. Digital Transmisison - Lin 15 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

16. 9/12/2004 4. Digital Transmisison - Lin 16 4.2 Block Encoding (cont.) Block Encoding Figure 4.15 Block Encoding, From p. 95, Data Communications and Networking, Forouzan, McGrawHill

17. 9/12/2004 4. Digital Transmisison - Lin 17 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

18. 9/12/2004 4. Digital Transmisison - Lin 18 4.2 Block Encoding (cont.) 4B/5B Encoding Table Table 4.1 4B/5B Encoding, From p. 97, Data Communications and Networking, Forouzan, McGrawHill DataCodeDataCode 000011110100010010 000101001100110011 001010100101010110 001110101101110111 010001010110011010 010101011110111011 011001110111011100 011101111111111101

19. 9/12/2004 4. Digital Transmisison - Lin 19 4.2 Block Encoding (cont.) 4B/5B Encoding Table Table 4.1 4B/5B Encoding, From p. 97, Data Communications and Networking, Forouzan, McGrawHill DataCode Q (Quiet)00000 I (Idle)11111 H (Halt)00100 J (start delimiter)11000 K (start delimiter)10001 T (end delimiter)01101 S (Set)11001 R (Reset)00111

20. 9/12/2004 4. Digital Transmisison - Lin 20 4.2 Block Encoding (cont.) 8B/6T Encoding –2 8 : 256 possibilities –3 6 : 729 six-symbol ternary signal Figure 4.17 Example of 8B/6T Encoding, From p. 98, Data Communications and Networking, Forouzan, McGrawHill

21. 9/12/2004 4. Digital Transmisison - Lin 21 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

22. 9/12/2004 4. Digital Transmisison - Lin 22 4.3 Sampling (cont.) PAM Figure 4.18 PAM, From p. 99, Data Communications and Networking, Forouzan, McGrawHill

23. 9/12/2004 4. Digital Transmisison - Lin 23 4.3 Sampling (cont.) Quantized PAM Signal Figure 4.19 Quantized PAM Signal, From p. 100, Data Communications and Networking, Forouzan, McGrawHill

24. 9/12/2004 4. Digital Transmisison - Lin 24 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

25. 9/12/2004 4. Digital Transmisison - Lin 25 4.3 Sampling (cont.) PCM Figure 4.21 PCM, From p. 101, Data Communications and Networking, Forouzan, McGrawHill

26. 9/12/2004 4. Digital Transmisison - Lin 26 4.3 Sampling (cont.) PCM Figure 4.22 From analog signal to PCM digital code, From p. 101, Data Communications and Networking, Forouzan, McGrawHill

27. 9/12/2004 4. Digital Transmisison - Lin 27 4.3 Sampling (cont.) Nyquist Theorem –Sampling rate must be at least 2 times the highest frequency Figure 4.23 Nyquist Theorem, From p. 102, Data Communications and Networking, Forouzan, McGrawHill = x Hz = 2 x samples = ½ x

28. 9/12/2004 4. Digital Transmisison - Lin 28 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

29. 9/12/2004 4. Digital Transmisison - Lin 29 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)

30. 9/12/2004 4. Digital Transmisison - Lin 30 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

31. 9/12/2004 4. Digital Transmisison - Lin 31 4.4 Transmission Mode Parallel Serial –Synchronous –Asynchronous Figure 4.25 Parallel transmission, From p. 104, Data Communications and Networking, Forouzan, McGrawHill

32. 9/12/2004 4. Digital Transmisison - Lin 32 4.4 Transmission Mode Serial Transmission Figure 4.26 Serial transmission, From p. 105, Data Communications and Networking, Forouzan, McGrawHill

33. 9/12/2004 4. Digital Transmisison - Lin 33 4.4 Transmission Mode Serial - Asynchronous Figure 4.27Asynchronlus transmission, From p. 106, Data Communications and Networking, Forouzan, McGrawHill

34. 9/12/2004 4. Digital Transmisison - Lin 34 4.4 Transmission Mode Serial - Synchronous Figure 4.28 Synchronlus transmission, From p. 107, Data Communications and Networking, Forouzan, McGrawHill

35. 9/12/2004 4. Digital Transmisison - Lin 35 Summary Questions?