1. Sami Al-Wakeel 1 Data Transmission and Computer Networks Data Encoding

2. Sami Al-Wakeel 2 Data Encoding Analog and digital data can be encoded into either digital or analog signal, creating four possible combinations: 1- Digital Data, Digital Signal. 2- Analog Data, Digital Signal. 3- Digital Data, Analog Signal. 4- Analog Data, Analog Signal.

3. Sami Al-Wakeel 3 Data Encoding 1. Digital Data, Digital Signals: Binary data are transmitted by encoding each data bit into signal element. Factors determine how successful the receiver will interpret the incoming signal: – An increase in data rate increases bit error rate. – An increase in S/N decreases bit error rate. – An increase in bandwidth allows an increase in data rate.

4. Sami Al-Wakeel 4 Data Encoding 1. Digital Data, Digital Signals (Continued): Polar NRZ RZ Biphase NRZ-L Manchester Differential Manchester NRZI Bipolar AMI B8ZS HDB3 Digital Signal Encoding

5. Sami Al-Wakeel 5 Data Encoding 1. Digital Data, Digital Signals (Continued):

6. Sami Al-Wakeel 6 Data Encoding 1. Digital Data, Digital Signals (Continued):

7. Sami Al-Wakeel 7 Data Encoding 1. Digital Data, Digital Signals (Continued): Digital signal Encoding Formats: I. NonReturn-to-Zero-Level (NRZ-L) Encoding: A negative voltage is equated with binary 1 and a positive voltage with binary 0. II. NonReturn to Zero Inverted (NRZI) Encoding: Binary 0 is represented by no transition at the beginning of bit interval, and binary 1 is represented by a transition at beginning of bit interval.

8. Sami Al-Wakeel 8 Data Encoding 1. Digital Data, Digital Signals (Continued): Advantages of NRZ: – The NRZ codes are simple and make efficient use of bandwidth. Disadvantages of NRZ: – Lack of synchronization capability. Consider a long string of 1’s or 0’s for NRZ-L, or a long string of 0’s for NRZI, the output is a constant voltage over a long period of time.

9. Sami Al-Wakeel 9 Data Encoding 1. Digital Data, Digital Signals (Continued): III. Bipolar-AMI Encoding: A binary 0 is represented by no line signal, and a binary 1 is represented by a positive or negative pulse. The binary 1 pulse must alternate in polarity. IV. Pseudoternary Encoding: A binary 1 is represented by no line signal, and a binary 0 by alternating positive or negative pulses.

10. Sami Al-Wakeel 10 Data Encoding 1. Digital Data, Digital Signals (Continued): Advantages of Bipolar-AMI or Pseudoternary: – No loss of synchronization if long string of binary 1’s occurs in the case of AMI or 0’s in the case of Pseudoternary. – The pulse alternation property provides a simple means of error detection. Disadvantages of Bipolar-AMI or Pseudoternary: – Long string of binary 0’s in the case of AMI or 1’s in the case of Pseudoternary still present a problem. – Multilevel binary signal requires approximately 3 dB more signal power than a two-valued signal for the same probability of bit error.

11. Sami Al-Wakeel 11 Data Encoding 1. Digital Data, Digital Signals (Continued): V. Manchester Encoding: There is a transition at the middle of each bit period. The mid-bit transition serves as a clocking mechanism and also as data. A low-to high transition represents a binary 1, and a high-to-low transition represents a binary 0.

12. Sami Al-Wakeel 12 Data Encoding 1. Digital Data, Digital Signals (Continued): VI. Differential Manchester Encoding: There is a transition at the middle of each bit period. The mid-bit transition is used only to provide clocking. A binary 0 is represented by the presence of a transition at the beginning of a bit period, and a binary 1 is represented by the absence of a transition at the beginning of a bit period

13. Sami Al-Wakeel 13 Data Encoding 1. Digital Data, Digital Signals (Continued): Advantages of Manchester and Differential Manchester Encoding: – Synchronization: Because this is a transition at the middle of each bit period. – Error Detection: The absence of the expected transition can be used to detect errors. Disadvantages of Manchester and Differential Manchester Encoding: – High Signaling Rate: At least one transition per bit time is needed, and may have at maximum two transitions. Therefore, the maximum modulation rate (rate at which signal level is changed) is twice that for NRZ; this means the required bandwidth is greater.

14. Sami Al-Wakeel 14 Data Encoding Modulation Rate: Modulation rate is the rate at which signal elements are generated. Maximum101010 … Minimum 1.0 0 (all 0’s or 1’s) NRZ-L 1.0 (al1’s)0.50 (all 0’s)NRZI 1.0 0 (all 0’s)Bipolar-AMI 1.0 0 (all 1’s)Pseudoternary 2.0 (all 0’s or 1’s)1.0 1.0 (101010 …) Manchester 2.0 (all 0’s)1.51.0 (all 1’s) Differential Manchester

15. Sami Al-Wakeel 15 Data Encoding 1. Digital Data, Digital Signals (Continued): VII. Bipolar with 8-zeros substitution (B8ZS): The coding scheme is based on a bipolar-AMI. The encoding is updated with the following rules: – If an octet of all zeros occurs and the last voltage pulse preceding this octet was positive, then the eight zeros of the octet are encoded as 0 0 0 + - 0 - +. – If an octet of all zeros occurs and the last voltage pulse preceding this octet was negative, then the eight zeros of the octet are encoded as 0 0 0 - + 0+ -.

16. Sami Al-Wakeel 16 Data Encoding 1. Digital Data, Digital Signals (Continued): VII. Bipolar with 8-zeros substitution (B8ZS): + Polarity of previous bit 00000000 +-0-+000 + Violation - Polarity of previous bit 00000000 -+0+-000 - Violation

17. Sami Al-Wakeel 17 Data Encoding 1. Digital Data, Digital Signals (Continued): VIII. High-density Bipolar-3 zeros (HDB3): HDB3 is based on the AMI encoding. HDB3 replaces strings of 4 zeros with sequences containing one or two pulses. In each case, the fourth zero is replaced with a code violation. In addition, successive violations are of alternate polarity. Thus, if the last violation was positive, this violation must be negative, and vice versa.

18. Sami Al-Wakeel 18 Data Encoding 1. Digital Data, Digital Signals (Continued): VIII. HDB3(Continued): The following table shows the HDB3 substitution rules: Number of Bipolar Pulses (Ones) Since Last Substitution Polarity of Preceding Pulse EvenOdd + 0 0 +0 0 0 -- - 0 0 -0 0 0 ++

19. Sami Al-Wakeel 19 Data Encoding 1. Digital Data, Digital Signals (Continued): VIII. HDB3(Continued): 0000 +000 0000 -000 - - + + 0000 -00- 0000 +00+ - - + +

20. Sami Al-Wakeel 20 Data Encoding

21. Sami Al-Wakeel 21 Data Encoding 2. Digital Data, Analog Signals: The most familiar of use of this transformation is for transmitting digital data through the public telephone network. The telephone network is designed to transmit, switch, and receive analog signals in the voice-frequency range of about 300 to 3400 Hz. A telephone line will not pass low-frequency signals that could occur if the data stream is made up of a continuous string of binary 1s or 0s. Thus digital devices are attached to the network via a modem (Modulator-demodulator) which coverts digital data to analog signals, and vice versa.

22. Sami Al-Wakeel 22 Data Encoding 2. Digital Data, Analog Signals (Continued):

23. Sami Al-Wakeel 23 Definitions

24. Sami Al-Wakeel 24 Data Encoding 2. Digital Data, Analog Signals (Continued): Encoding Techniques: There are three basic encoding or modulation techniques for transforming digital data into analog signals: – Amplitude-Shift Keying (ASK). – Frequency-Shift Keying (FSK). – Phase-Shift Keying (PSK).

25. Sami Al-Wakeel 25 Data Encoding 2. Digital Data, Analog Signals:

26. Sami Al-Wakeel 26 Data Encoding 2. Digital Data, Analog Signals: Bit rate is the number of bits per second. Baud rate is the number of signal elements per second. The baud rate equals the bit rate divided by the number of bits represented by each signal element. The carrier signal is a high-frequency signal that acts as a basis for information signal. The receiving device is turned to the frequency of the carrier signal that it expects from the sender.

27. Sami Al-Wakeel 27 Data Encoding 2. Digital Data, Analog Signals (Continued): Encoding Techniques: ASK FSK PSK QAM Digital/analog Encoding

28. Sami Al-Wakeel 28 Data Encoding 2. Digital Data, Analog Signals: I. Amplitude-Shift Keying:

29. Sami Al-Wakeel 29 Data Encoding 2. Digital Data, Analog Signals (Continued): I. Amplitude-Shift Keying (ASK): We can represent a unipolar periodic signal, v d (t), with unity amplitude and fundamental frequency w 0 as: We can represent the carrier signal as: ASK can be represented mathematically as:

30. Sami Al-Wakeel 30 Data Encoding 2. Digital Data, Analog Signals (Continued): I. Amplitude-Shift Keying (ASK): However:

31. Sami Al-Wakeel 31 Data Encoding 2. Digital Data, Analog Signals: II. Frequency-Shift Keying:

32. Sami Al-Wakeel 32 Data Encoding 2. Digital Data, Analog Signals (Continued): II. Frequency-Shift Keying (FSK): FSK can be represented mathematically as: w 1 and w 2 are the two carrier frequencies in radians per second.

33. Sami Al-Wakeel 33 Data Encoding 2.Digital Data, Analog Signals (Continued): II. Frequency-Shift Keying (FSK): An example of use of FSK for full-duplex operation over the PSTN. The PSTN will pass frequencies in the approximate range 300 to 3400 Hz. To achieve full-duplex, the bandwidth is split at 1700 Hz. In one direction, the frequencies used to represent 1 and 0 are centered on 1170 Hz. Similarly, for the opposite direction, the frequencies used to represent 1 and 0 are centered on 2125 Hz

34. Sami Al-Wakeel 34 Data Encoding 2. Digital Data, Analog Signals:

35. Sami Al-Wakeel 35 Data Encoding 2. Digital Data, Analog Signals: III. Phase-Shift Keying:

36. Sami Al-Wakeel 36 Definitions Relationship between different phases:

37. Sami Al-Wakeel 37 Data Encoding 2. Digital Data, Analog Signals (Continued): Multilevel Modulation Methods: More efficient use of bandwidth can be achieved if each signaling element represents more than one bit. For example, instead of a phase shift of 180 , Quadrature Phase-Shift Keying (QPSK) or (4-PSK) technique uses phase shifts of multiple of 90 .

38. Sami Al-Wakeel 38 Data Encoding 2. Digital Data, Analog Signals (Continued): 4-PSK:

39. Sami Al-Wakeel 39 Data Encoding 8-PSK: PhaseTribit 0000 45001 90010 135011 180100 225101 270110 315111

40. Sami Al-Wakeel 40 Data Encoding 2. Digital Data, Analog Signals (Continued): Quadrature Amplitude Modulation (QAM). Higher bit rates are achieved using 8 and even 16 phase changes. In practice, however, there is a limit to how many phases can be used. Hence to increase the bit rate further, it is more common to introduce amplitude as well as phase variations of each vector. This type of modulation is then known as Quadrature Amplitude Modulation (QAM). 16-QAM has 16 levels per signal element, and hence 4- bit symbols.

41. Sami Al-Wakeel 41 Data Encoding 2. Digital Data, Analog Signals (Continued): 4-QAM (1 amplitude, 4 phases):

42. Sami Al-Wakeel 42 Data Encoding 2. Digital Data, Analog Signals (Continued): 8-QAM (2 amplitudes, 4 phases):

43. Sami Al-Wakeel 43 Data Encoding 2. Digital Data, Analog Signals (Continued): 16-QAM ( 4 amplitudes, 8 phases):

44. Sami Al-Wakeel 44 Data Encoding 2. Digital Data, Analog Signals (MODEMS): A modem converts the digital signal generated by the computer into an analog signal to be carried by a public phone line. It is also converts the analog signals receiver over a phone line into digital signals usable by the computer. The term modem is composite word that refers to a signal modulator and a signal demodulator. A modulator treats a digital signal as a series of 1s and 0s, and so can transform it into an analog signal by using the digital-to-analog mechanisms of ASK, FSK, PSK, and QAM.

45. Sami Al-Wakeel 45 Data Encoding 2. Digital Data, Analog Signals (MODEMS):

46. Sami Al-Wakeel 46 Data Encoding 2. Digital Data, Analog Signals (MODEMS): Telephone Line Bandwidth:

47. Sami Al-Wakeel 47 Data Encoding Modem Speeds: Theoretical Bit Rates for Modems: Full-DuplexHalf-DuplexEncoding 12002400ASK, FSK, 2-PSK 240048004-PSK, 4 QAM 360072008-PSK, 8-QAM 4800960016-QAM 60001200032-QAM 72001440064-QAM 840016800128-QAM 960019200256-QAM

48. Sami Al-Wakeel 48 Data Encoding 3. Analog Data, Digital Signals: A process of converting analog data into digital data, which process is known as digitization. The device used for converting analog data into digital form for transmission, and subsequently recovering the original data from the digital is known as a codec (coder-decoder)

49. Sami Al-Wakeel 49 Data Encoding 3. Analog Data, Digital Signals (Continued): Voice transmissions are limited to a maximum bandwidth of less than 4 KHz. To Convert such signals into digital form, the Nyquest sampling theorem states: If a signal f(t) is sampled at regular intervals of time and at the rate higher than twice the highest frequency component, then the samples contain all the information of the original signal. The function f(t) may be reconstructed from these samples.

50. Sami Al-Wakeel 50 Data Encoding 3. Analog Data, Digital Signals (Continued): Hence to convert a 4 KHz voice signal into digital form, it must be sampled at rate of 8000 times per second. The sampled signal is first converted into a pulse stream, the amplitude of each pulse being equal to the amplitude of the original analog signal at the sampling instant. The resulting signal is known as a pulse amplitude modulated (PAM) signal. The PAM signal is still analog since its amplitude can vary over the full amplitude range.

51. Sami Al-Wakeel 51 Data Encoding 3. Analog Data, Digital Signals (Continued): It is converted into an all-digital form by quantizing each pulse into its equivalent binary form. If eight bits are used to quantize each PAM signal, then 256 distinct levels are used. The resulting digital signal is known as a pulse code modulated (PCM) signal and has a bit rate of 64 kbps – 8000 sample per second each of 8 bits.

52. Sami Al-Wakeel 52 Data Encoding 3. Analog Data, Digital Signals:

53. Sami Al-Wakeel 53 Data Encoding 3. Analog Data, Digital Signals: