1. Digital Transmission & Analog Transmission

2. 4.#2 1. DIGITAL-TO-DIGITAL CONVERSION Digital Data -> Digital Signal Three techniques: 1.line coding (always needed) 2.block coding (working with NRZ-I) 3.Scrambling (working with AMI)

3. Figure 4.1 Line coding and decoding

4. Figure 4.2 Signal element versus data element r = number of data elements / number of signal elements

5. Data Rate Vs. Signal Rate Data rate: the number of data elements (bits) sent in 1s (bps). It’s also called the bit rate Signal rate: the number of signal elements sent in 1s (baud). It’s also called the pulse rate, the modulation rate, or the baud rate. We wish to: 1. increase the data rate (increase the speed of transmission) 2. decrease the signal rate (decrease the bandwidth requirement) 3.Worst case, best case, and average case of r 4.S = c * N / r baud

6. Baseline wandering Baseline: running average of the received signal power DC Components Constant digital signal creates low frequencies Self-synchronization Receiver Setting the clock matching the sender’s

7. Figure 4.4 Line coding schemes

8. Figure 4.5 Unipolar NRZ scheme

9. Figure 4.6 Polar NRZ-L and NRZ-I schemes

10. Figure 4.7 Polar RZ scheme

11. Figure 4.8 Polar biphase: Manchester and differential Manchester schemes

12. High=0, Low=1 No change at begin=0, Change at begin=1 H-to-L=0, L-to-H=1 Change at begin=0, No change at begin=1

13. Figure 4.9 Bipolar schemes: AMI (Alternate Mark Inversion) and pseudoternary

14. Multilevel Schemes In mBnL schemes, a pattern of m data elements is encoded as a pattern of n signal elements in which 2 m ≤ L n m: the length of the binary pattern B: binary data n: the length of the signal pattern L: number of levels in the signaling

15. Figure 4.10 Multilevel: 2B1Q scheme

16. Figure 4.13 Multitransition: MLT-3 scheme

17. Table 4.1 Summary of line coding schemes Polar

18. Block Coding Redundancy is needed to ensure synchronization and to provide error detecting Block coding is normally referred to as mB/nB coding it replaces each m-bit group with an n-bit group m < n

19. Figure 4.15 Using block coding 4B/5B with NRZ-I line coding scheme

20. Figure 4.14 Block coding concept

21. Table 4.2 4B/5B mapping codes

22. Scrambling It modifies the bipolar AMI encoding (no DC component, but having the problem of synchronization) It does not increase the number of bits It provides synchronization It uses some specific form of bits to replace a sequence of 0s

23. Figure 4.19 Two cases of B8ZS scrambling technique B8ZS substitutes eight consecutive zeros with 000VB0VB

24. Figure 4.20 Different situations in HDB3 scrambling technique HDB3 substitutes four consecutive zeros with 000V or B00V depending on the number of nonzero pulses after the last substitution.

25. 2. ANALOG-TO-DIGITAL CONVERSION The tendency today is to change an analog signal to digital data. 1.pulse code modulation 2.delta modulation.

26. Figure 4.21 Components of PCM encoder

27. According to the Nyquist theorem, the sampling rate must be at least 2 times the highest frequency contained in the signal. What can we get from this: 1. we can sample a signal only if the signal is band-limited 2. the sampling rate must be at least 2 times the highest frequency, not the bandwidth

28. Figure 4.26 Quantization and encoding of a sampled signal

29. Contribution of the quantization error to SNR db SNR db = 6.02n b + 1.76 dB n b : bits per sample (related to the number of level L) The minimum bandwidth of the digital signal is n b times greater than the bandwidth of the analog signal. B min = n b x B analog

30. DM (delta modulation) finds the change from the previous sample Next bit is 1, if amplitude of the analog signal is larger Next bit is 0, if amplitude of the analog signal is smaller

31. 3. TRANSMISSION MODES 1. The transmission of binary data across a link can be accomplished in either parallel or serial mode. 2. In parallel mode, multiple bits are sent with each clock tick. 3. In serial mode, 1 bit is sent with each clock tick. 4. there are three subclasses of serial transmission: asynchronous, synchronous, and isochronous.

32. Figure 4.31 Data transmission and modes

33. 4. DIGITAL-TO-ANALOG CONVERSION Digital-to-analog conversion is the process of changing one of the characteristics of an analog signal based on the information in digital data.

34. Figure 5.1 Digital-to-analog conversion

35. Figure 5.2 Types of digital-to-analog conversion

36. 1.Data element vs. signal element What is a signal element here? 2. Bit rate is the number of bits per second. 2. Baud rate is the number of signal elements per second. 3. In the analog transmission of digital data, the baud rate is less than or equal to the bit rate. S = N x 1/r baud r = log 2 L

37. Figure 5.3 Binary amplitude shift keying B = (1+d) x S = (1+d) x N x 1/r

38. Figure 5.4 Implementation of binary ASK

39. Figure 5.6 Binary frequency shift keying

40. Figure 5.9 Binary phase shift keying

41. Figure 5.12 Concept of a constellation diagram

42. Figure 5.13 Three constellation diagrams

43. QAM – Quadrature Amplitude Modulation Modulation technique used in the cable/video networking world Instead of a single signal change representing only 1 bps – multiple bits can be represented buy a single signal change Combination of phase shifting and amplitude shifting (8 phases, 2 amplitudes)

44. Figure 5.14 Constellation diagrams for some QAMs

45. 5. ANALOG AND DIGITAL Analog-to-analog conversion is the representation of analog information by an analog signal. Modulation is needed if the medium is bandpass in nature or if only a bandpass channel is available to us. Example: radio stations

46. Figure 5.15 Types of analog-to-analog modulation

47. Figure 5.16 Amplitude modulation The total bandwidth required for AM can be determined from the bandwidth of the audio signal: B AM = 2B.

48. Figure 5.17 AM band allocation

49. Figure 5.18 Frequency modulation

50. Figure 5.19 FM band allocation The total bandwidth required for FM can be determined from the bandwidth of the audio signal: B FM = 2(1 + β)B. β has a common value of 4

51. Figure 5.20 Phase modulation The total bandwidth required for PM can be determined from the bandwidth and maximum amplitude of the modulating signal: B PM = 2(1 + β)B.