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Dr. Paramjeet Singh HoD, Dept . of CSE PTU GZS Campus Bathinda Subject: Computer Networks

Dr. Paramjeet Singh HoD, Dept . of CSE PTU GZS Campus Bathinda Subject: Computer Networks Topic: Encoding and modulating. Encoding. Encoding is the process of converting data from one form to another. Types of encoding Analog to analog encoding Analog to digital encoding

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Dr. Paramjeet Singh HoD, Dept . of CSE PTU GZS Campus Bathinda Subject: Computer Networks

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  1. Dr. Paramjeet Singh HoD,Dept. of CSE PTU GZS Campus Bathinda Subject: Computer Networks Topic: Encoding and modulating Punjab EDUSAT Society

  2. Encoding • Encoding is the process of converting data from one form to another. • Types of encoding • Analog to analog encoding • Analog to digital encoding • Digital to analog encoding • Digital to digital encoding Punjab EDUSAT Society

  3. Analog Signals Analog signal is a continuous waveform that changes smoothly over time. It has three characteristics Amplitude - Height of the signal Frequency – Rate of change w.r.t. time Phase – Position of waveform relative to time zero. Punjab EDUSAT Society

  4. Digital Signal refers to something that is discrete. Bit interval (instead of period) and Bit rate (instead of frequency) The bit interval is the time required to send one single bit. The bit rate is the number of bit intervals in one second, usually expressed in bits per second (bps). Punjab EDUSAT Society

  5. Data rate and Baud rate The baud or signal rate can be expressed as: S = c x N x 1/r bauds where N is data rate c is the case factor (worst, best & avg.) r is the ratio between data element & signal element Punjab EDUSAT Society

  6. Analog to analog encoding Analog modulation: Modulation is the process by Which some characteristics of the carrier signal is varied in accordance with the modulating signal. These characteristics may be Amplitude Frequency Phase Punjab EDUSAT Society

  7. Need of modulation To reduce the height of antena, h=wavelength/4 Where wavelength = C/ F, C = Speed of light and F=Frequency 2. To avoid the intermixing of signals of different stations. 3. It increases the radiation power. Punjab EDUSAT Society

  8. Amplitude modulation It is the process by which the amplitude of the carrier signal is varied in accordance with the amplitude of the modulating signal. The frequency and phase of the carrier remain the same Punjab EDUSAT Society

  9. Amplitude Modulation Punjab EDUSAT Society

  10. Amplitude modulation Bandwidth Punjab EDUSAT Society

  11. Amplitude modulation Band Allocation Punjab EDUSAT Society

  12. Frequency modulation It is the process by which the frequency of the carrier signal is varied in accordance with the amplitude of the modulating signal. The amplitude and phase of the carrier remain the same. Punjab EDUSAT Society

  13. Frequency Modulation Punjab EDUSAT Society

  14. FM Bandwidth Punjab EDUSAT Society

  15. FM Band Allocation Punjab EDUSAT Society

  16. Phase modulation It is the process by which the phase of the carrier signal is varied in accordance with the amplitude of the modulating signal. The amplitude and frequency of the carrier remain the same. Punjab EDUSAT Society

  17. Analog to Digital Encoding Punjab EDUSAT Society

  18. Pulse amplitude modulation (PAM) This technique takes analog signal, sample it and generate a series of pulses based on the sampling. The term sampling means measuring the amplitude of the signal at equal interval. Punjab EDUSAT Society

  19. Pulse amplitude modulation (PAM) Punjab EDUSAT Society

  20. Quantized PAM Signal Punjab EDUSAT Society

  21. Quantizing Using Sign and Magnitude Punjab EDUSAT Society

  22. Pulse amplitude modulation (PAM) PAM is not much useful in data communications. The reason behind this that, although it translates the original wave form to a series of pulses but these pluses are still of any amplitude (still an analog signal, not digital). To make them digital,we must modify them by using pulse code modification(PCM). PAM is the foundation of PCM technique. Punjab EDUSAT Society

  23. Pulse code modulation (PCM) It modify the pulses created by PAM to create a completely digital signals. To do so , the PCM first quantities the PAM pulses. Then each value is translated into its seven –bits binary equivalent. The eighth bit indicates the sign. It uses digital to digital encoding techniques. Punjab EDUSAT Society

  24. Pulse code modulation (PCM) • Phases of PCM • PAM • Quantization • Binary encoding • Digital to digital encoding Punjab EDUSAT Society

  25. From Analog to PCM Punjab EDUSAT Society

  26. Quantization Quantization is the method of assigning internal values in a specific range to sampled instances. Binary Encoding Binary encoding calculate 7 bit binary equivalent of each quantized value. The eighth bit indicate the sign. Punjab EDUSAT Society

  27. Nyquist Theorem PCM is based on the sampling theorem, which states that if a signal f(t) is sampled at regular intervals of time and at a rate higher then twice the highest signal frequency, then the samples contains all the information of the original signal and the function f(t) may be reconstructed from these samples . Sampling (fs)>=2*f(highest signal frequency ) samples/seconds Punjab EDUSAT Society

  28. Nyquist Theorem Punjab EDUSAT Society

  29. Delta Modulation (DM) • The basic idea in delta modulation is to approximate the derivative of analog signal rather than its amplitude. • The analog data is approximated by a staircase function that moves up or down by one quantization level at each sampling time. • Output of DM is a single bit. • PCM preferred because of better SNR characteristics. Punjab EDUSAT Society

  30. Delta Modulation Punjab EDUSAT Society

  31. DM is the simplest form of differential pulse-code modulation (DPCM) where the difference between successive samples are encoded into n-bit data streams. In this, the transmitted data is reduced to a 1-bit data stream. Its main features are: 1. The analog signal is approximated with a series of segments. 2. Each segment of the approximated signal is compared to the original analog wave to determine the increase or decrease in relative amplitude. Punjab EDUSAT Society

  32. 3. The decision process for establishing the state of successive bits is determined by this comparison 4. Only the change of information is sent, that is, only an increase or decrease of the signal amplitude from the previous sample is sent whereas a no-change condition causes the modulated signal to remain at the same 0 or 1 state of the previous sample. Punjab EDUSAT Society

  33. Digital to Analog Encoding: • Process of changing one of the characteristics of an analog signal based on the digital signal (1 or 0). • It has following types: • Amplitude Shift Keying (ASK) • Frequency Shift Keying (FSK) • Phase Shift Keying (PSK) • Quadrature Amplitude Modulation (QAM) Punjab EDUSAT Society

  34. ASK: Strength of the carrier signal is varied to represent binary 1 or 0. Punjab EDUSAT Society

  35. Bandwidth for ASK Punjab EDUSAT Society

  36. FSK: Frequency of the carrier signal is varied to represent binary 1 or 0. Punjab EDUSAT Society

  37. Bandwidth for FSK Punjab EDUSAT Society

  38. PSK: Phase of the carrier signal is varied to represent binary 1 or 0. Punjab EDUSAT Society

  39. PSK Constellation Punjab EDUSAT Society

  40. 4-PSK Punjab EDUSAT Society

  41. 4-PSK Characteristics Punjab EDUSAT Society

  42. 8-PSK Characteristics Punjab EDUSAT Society

  43. PSK Bandwidth Punjab EDUSAT Society

  44. QAM: Combining ASK and PSK in such a way that we have maximum contrast between each bit, dibit, tribit, quadbit, and so on. Punjab EDUSAT Society

  45. 8-QAM Signal Punjab EDUSAT Society

  46. 16-QAM Constellation Punjab EDUSAT Society

  47. Digital to digital encoding It is the representation of digital information to digital signal. Punjab EDUSAT Society

  48. Types of Digital to Digital Encoding Punjab EDUSAT Society

  49. Unipolar:- It uses only one level of value and polarity (all signal elements have the same algebraic sign i.e. all positive or negative). Advantages :- • Very simple. Disadvantages :- • DC component. • Synchronization. Punjab EDUSAT Society

  50. DC component :- The average amplitude of a unipolar encoded signal is non zero. • This creates direct current (DC) component(with zero frequency). • Synchronization :- when a signal is unvarying, the receiver can not determine the beginning and ending of each bit. Therefore, A synchronization problem in unipolar can occur when ever the data stream includes a long uninterrupted series of 1’s or 0’s. Punjab EDUSAT Society

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