introduction to communication engineering.pptx

INTRODUCTION TO COMMUNICATION ENGINEERING
UNIT-1
ANALOG MODULATION
Amplitude modulation
DSBSC,SSBSC,VSB
Angle modulation
PM and FM modulation
Superheterodyne receiver

Nyquist Rate
Sampling Theorem

1. J.N.N INSTITUTE OF ENGINEERING EC8395 – COMMUNICTION ENGINEERING– 3 rd SEMESTER R.CHANDRALEKHA Department of Computer science and Engineering

2. UNIT-1 ANALOG MODULATION Amplitude modulation DSBSC,SSBSC,VSB Angle modulation PM and FM modulation Superheterodyne receiver TOPICS TO BE COVERED

3. Amplitude modulation is the process by which amplitude of the carrier signal is varied in accordance with the intendances value (amplitude) of the modulating signal, but frequency and phase of carrier wave is constant. Amplitude modulation classified as 1.DSB-SC (double side band-suppressed carrier) 2.SSB-SC (single side band-suppressed carrier) 3.VSB (vestigial side band) Amplitude modulation

4. Mathematical representation of AM

5. MODULATION INDEX: Ratio between amplitude of message signal to amplitude of carrier signal is called as modulation index or modulation factor or dept of modulation or modulation coefficient. Ma= Vm / Vc Percentage of modulation If the modulation index is expressed in percentage then it is called as percentage modulation. % modulation= Vm /Vcx100 It describes the amount of amplitude change present in AM envelope. Deminension less quantity

6. Waveform representation of AM

7. Frequency spectrum and bandwidth of AM Equation 5,

8. Frequency spectrum of AM

9. BANDWIDTH Bandwidth of the signal can be obtained by taking the difference highest and lowest frequencies. Equation 6, BW= Fusb-Flsb =( fc+fm )-( fc -fm) Equation 7, Bw =2fm Therefore bandwidth of AM signal is twice of the maximum frequency of modulating signal.

10. PHASOR (OR) VECTOR REPRESENTATION OF AM

11. Equation 8, Fusb = fc+fm Flsb = fc -fm Equation 9, Ma= Vmax-Vmin \2 Vmax+Vmin /2 Ma= Vmax-Vmin / Vmax+Vmin Calulation of AM Modulation

12. We know that AM signal has 3-components 1.unmodulated carrier(Pc) 2.lower sideband ( Plsb ) 3.Upper sideband ( Pusb ) Pt= Pc+Plsb+Pusb AM power distributed

13. For carrier power (Pc): Where, Vc –peak carrier voltage (volts) R-load resistance (ohms)

14. POWER SPECTRUM OF AM

15. Amplitude Modulation In amplitude  modulation , the amplitude of the carrier signal is varied in correspondence with the amplitude of the modulating signal by maintaining frequency and phase at constant. Here, is the pictorial representation of amplitude modulation. TYPES OF ANALOG MODULATION

16. Frequency Modulation In frequency modulation, the frequency of the carrier signal is varied in correspondence with the amplitude of the modulating signal by maintaining amplitude and phase at constant. Here, is the pictorial representation of frequency modulation. Frequency Modulation

17. Phase Modulation In phase modulation, the phase of the carrier signal is varied in correspondence with the amplitude of the modulating signal by maintaining amplitude and frequency at constant. Here, is the pictorial representation of phase modulation. Phase Modulation

18. DSB-SC is  transmission in which frequencies produced by amplitude modulation (AM) are symmetrically spaced above and below the  carrier frequency  and the carrier level is reduced to the lowest practical level, ideally being completely suppressed . In the DSB-SC modulation, unlike in AM, the wave carrier is not transmitted; thus, much of the power is distributed between the side bands, which implies an increase of the cover in DSB-SC, compared to AM, for the same power use DSB-SC transmission is a special case of  double-sideband reduced carrier transmission . It is used for  radio data systems . This mode is frequently used in  Amateur radio  voice communications, especially on High-Frequency bands. DSB-SC GENERATION

19. CONT…

20. For DSBSC, Coherent Demodulation is done by multiplying the DSB-SC signal with the carrier signal (with the same phase as in the modulation process) just like the modulation process. This resultant signal is then passed through a low pass filter to produce a scaled version of the original message signal. DEMODULATION

21. The process of suppressing one of the sidebands along with the carrier and transmitting a single sideband is called as  Single Sideband Suppressed Carrier  system or simply  SSBSC . It is plotted as shown in the following figure. SSBC-SC GENERATION

22. SSB-SC GENERATION

23. Vestigial Sideband (VSB) modulation is a modulation technique which allows  transmission of one sideband  in addition with  a part  or  vestige of the other . It is basically a compromise between  DSB-SC  and  SSB-SC. VSB MODULATION

24. High level transmitters use high level modulation, and low level transmitters use low level modulation. The choice between the two modulation schemes depends on the transmitting power of the AM transmitter. In broadcast transmitters, where the transmitting power may be of the order of kilowatts, high level modulation is employed. In low power transmitters, where only a few watts of transmitting power are required , low level modulation is used . AM TRANSMITTER 1.HIGH LEVEL TRANSMITTER

25. The low-level AM transmitter shown in the figure (b) is similar to a high-level transmitter, except that the powers of the carrier and audio signals are not amplified. These two signals are directly applied to the modulated class C power amplifier . 2. LOW LEVEL TRANSMITTER

26. The AM super heterodyne receiver takes the amplitude modulated wave as an input and produces the original audio signal as an output.  Selectivity  is the ability of selecting a particular signal, while rejecting the others.  Sensitivity  is the capacity of detecting RF signal and demodulating it, while at the lowest power level AM RECEIVER

27. Radio amateurs are the initial radio receivers. However, they have drawbacks such as poor sensitivity and selectivity. To overcome these drawbacks,  super heterodyne  receiver was invented.  SUPER HETERODYE RECEIVER

28. FM receiver is similar to the block diagram of AM receiver. The two blocks Amplitude limiter and De-emphasis network are included before and after FM demodulator. The operation of the remaining blocks is the same as that of AM receiver . FM TRANSMITTER

29. CLASSIFICATIONS: CLASSIFICATION OF FM

30. In direct FM generation, the instantaneous frequency of the carrier is changed directly in proportion with the message signal. For this, a device called voltage controlled oscillator (VCO) is used. A VCO can be implemented by using a sinusoidal oscillator with a tuned circuit having a high value of Q . REACTANCE MODULATOR DIRECT METHOD

31. Pulse-code modulation (PCM) is  a method used to digitally represent sampled analog signals .In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps . UNIT-2 PULSE MODULATION

32. Sampling  is defined as, “The process of measuring the instantaneous values of continuous-time signal in a discrete form .” Sampling Rate To discretize the signals, the gap between the samples should be fixed. That gap can be termed as a  sampling period T s . Sampling Frequency =1/ Ts =fs SAMPLING PROCESS

33. Suppose that a signal is band-limited with no frequency components higher than  W  Hertz. That means,  W  is the highest frequency. For such a signal, for effective reproduction of the original signal, the sampling rate should be twice the highest frequency. Nyquist Rate

34. The sampling theorem, which is also called as  Nyquist theorem , delivers the theory of sufficient sample rate in terms of bandwidth for the class of functions that are bandlimited. The sampling theorem states that, “a signal can be exactly reproduced if it is sampled at the rate  f s  which is greater than twice the maximum frequency  W .” Sampling Theorem

35. The digitization of analog signals involves the rounding off of the values which are approximately equal to the analog values. The method of sampling chooses a few points on the analog signal and then these points are joined to round off the value to a near stabilized value. Such a process is called as  Quantization . QUANTIZATION

36. Pulse-code modulation  ( PCM ) is a method used to  digitally  represent sampled  analog signals . It is the standard form of  digital audio  in computers,  compact discs ,  digital telephony  and other digital audio applications. In a PCM  stream , the  amplitude  of the analog signal is  sampled  regularly at uniform intervals, and each sample is  quantized  to the nearest value within a range of digital steps. PULSE AMPLITUDE MODULATION

37. Block diagram

38. Differential pulse-code modulation  ( DPCM ) is a signal encoder that uses the baseline of  pulse-code modulation  (PCM) but adds some functionalities based on the prediction of the samples of the signal. The input can be an  analog signal  or a  digital signal . DIFFERENTIAL PULSE CODE MODULATION(DPCM)

39. Cont …

40. The block diagram of DPCM Receiver consists of a decoder, a predictor, and a summer circuit. Following is the diagram of DPCM Receiver. DPCM Receiver

41. The type of modulation, where the sampling rate is much higher and in which the stepsize after quantization is of a smaller value  Δ , such a modulation is termed as  delta modulation . Delta Modulation is a simplified form of DPCM technique, also viewed as  1-bit DPCM scheme . As the sampling interval is reduced, the signal correlation will be higher . The Delta Modulator comprises of a 1-bit quantizer and a delay circuit along with two summer circuits. DELTA MODULATION

42. T ransmitter Cont..

43. EXPRESSION

44. The delta demodulator comprises of a low pass filter, a summer, and a delay circuit. The predictor circuit is eliminated here and hence no assumed input is given to the demodulator . Delta Demodulator

45. In digital modulation, we have come across certain problem of determining the step-size, which influences the quality of the output wave. A larger step-size is needed in the steep slope of modulating signal and a smaller stepsize is needed where the message has a small slope. The minute details get missed in the process. So, it would be better if we can control the adjustment of step-size, according to our requirement in order to obtain the sampling in a desired fashion. This is the concept of  Adaptive Delta Modulation . Adaptive Delta Modulation  

46. To overcome the quantization errors due to slope overload and granular noise, the step size (δ) is made adaptive to variations in the input signal x(t). Particularly in the steep segment of the signal (t) , the step size is increased .When the input is varying slowly , the step size is reduced .Then the method is called Adaptive Delta Modulation(ADM). TRANSMITTER

47. The receiver has two portions. The first portion produces the step size from each incoming bit.Exactly the same process is followed as that in transmitter. The previous input and present input decide the step size. It is then applied to the second portion i.e., an accumulator which builds up staircase waveform. The low pass filter then smoothens out the staircase waveform to reconstruct the original signal. ADM RECEIVER

48. Adaptive Differential Pulse-Code Modulation (ADPCM) Need for coding speech at low bit rates , we have two aims in mind: 1 . Remove redundancies from the speech signal as far as possible. 2 . Assign the available bits in a perceptually efficient manner Adaptive Differential Pulse-Code Modulation (ADPCM)

49. AQB

50. APB

51. A channel vocoder is a device for compressing, or encoding, the data needed to represent a speech waveform, while still retaining the intelligibilty of the original waveform. The first channel vocoder was developed by Homer Dudley in 1936. It passed the speech signal through a bank of band-pass filters. These filters each covered a portion of the audio spectrum. The energy of each filter's output was then measured, or sampled, at regular time intervals and stored. This collection of filter energy samples then comprised the "coding" of the speech signal. This code could then be transmitted over a communication channel of lower bandwidth than would be neccessary for the raw speech signal. At the receiving end, the speech signal is reconstructed from this code by using the time sequence of filter energy samples to modulate the amplitude of a pulse signal being fed into a bank of filters similar to the ones used for the encoding. The result, while clearly not the original speech signal, is nonetheless intelligible, and one can, in most cases, understand what is being said. CHANNEL VOCODER

52. BLOCK DIAGRAM

53. In telecommunications,  frequency-division multiplexing  ( FDM ) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separate signal. This allows a single transmission medium such as a cable or optical fiber  to be shared by multiple independent signals. Another use is to carry separate serial bits or segments of a higher rate signal in parallel. MULTIPLEXING FREQUENCY DIVISION MULTIPLEXING(FDM)

54. Time-division multiplexing  ( TDM ) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern. This method transmits two or more digital signals or analog signals over a common channel. It can be used when the bit rate of the transmission medium exceeds that of the signal to be transmitted. This form of signal multiplexing was developed in  telecommunications for  telegraphy systems TIME DIVISION MULTIPLEXING(TDM)

55. TDM BLOCK DIAGRAM

56. UNIT-3 DIGITAL MODULATION & TRANSMISSION

57. Digital communications  is any exchange of data that transmits the data in a digital form. For example, communications done over the Internet is a form of digital communication. INTRODUCTION

58. This is also called as 2-phase PSK or Phase Reversal Keying. In this technique, the sine wave carrier takes two phase reversals such as 0° and 180 ° BPSK Modulator The block diagram of Binary Phase Shift Keying consists of the balance modulator which has the carrier sine wave as one input and the binary sequence as the other input. Following is the diagrammatic representation . Binary Phase Shift Keying  BPSK

59. The modulation of BPSK is done using a balance modulator, which multiplies the two signals applied at the input. For a zero binary input, the phase will be  0°  and for a high input, the phase reversal is of  180° . Following is the diagrammatic representation of BPSK Modulated output wave along with its given input. CONT…

60. The block diagram of BPSK demodulator consists of a mixer with local oscillator circuit, a bandpass filter, a two-input detector circuit. The diagram is as follows . By recovering the band-limited message signal, with the help of the mixer circuit and the band pass filter, the first stage of demodulation gets completed. The base band signal which is band limited is obtained and this signal is used to regenerate the binary message bit stream. BPSK Demodulator

61. DPSK the phase of the modulated signal is shifted relative to the previous signal element. No reference signal is considered here. The signal phase follows the high or low state of the previous element. This DPSK technique doesn’t need a reference oscillator . Differential Phase Shift Keying 

62. DPSK is a technique of BPSK, in which there is no reference phase signal. Here, the transmitted signal itself can be used as a reference signal. Following is the diagram of DPSK Modulator . DPSK Modulator

63. In DPSK demodulator, the phase of the reversed bit is compared with the phase of the previous bit. Following is the block diagram of DPSK demodulator . From the above figure, it is evident that the balance modulator is given the DPSK signal along with 1-bit delay input. That signal is made to confine to lower frequencies with the help of LPF. Then it is passed to a shaper circuit, which is a comparator or a Schmitt trigger circuit, to recover the original binary data as the output. DPSK Demodulator

64. CONT…

65. Instead of the conversion of digital bits into a series of digital stream, it converts them into bit pairs. This decreases the data bit rate to half, which allows space for the other users QPSK Modulator The QPSK Modulator uses a bit-splitter, two multipliers with local oscillator, a 2-bit serial to parallel converter, and a summer circuit. Following is the block diagram for the same. Quadrature Phase Shift Keying  QPSK

66. QPSK WAVEFORM

67. The QPSK Demodulator uses two product demodulator circuits with local oscillator, two band pass filters, two integrator circuits, and a 2-bit parallel to serial converter. Following is the diagram for the same. QPSK Demodulator

68. QAM (quadrature amplitude modulation) is a method of combining two amplitude  modulation  (AM) signals into a single  channel . This approach helps double its effective  bandwidth . QAM is also used with pulse AM ( PAM ) in digital systems, like  wireless applications. QAM MODULATION Quadrature amplitude modulation

69. CONT…

70. QAM Demodulator

71. DUOBINARY SIGNALING

72. MODIFIED DUOBINARY SIGNALING

73. UNIT IV INFORMATION THEORY AND CODING

74. Amount of Information

75. Average Information or Entropy

76. Properties of entropy

77. Source Coding

78. A Shannon–Fano tree is built according to a specification designed to define an effective code table. The actual algorithm is simple: For a given list of symbols, develop a corresponding list of probabilities or frequency counts so that each symbol’s relative frequency of occurrence is known. Sort the lists of symbols according to frequency, with the most frequently occurring symbols at the left and the least common at the right. Divide the list into two parts, with the total frequency counts of the left part being as close to the total of the right as possible. The left part of the list is assigned the binary digit 0, and the right part is assigned the digit 1. This means that the codes for the symbols in the first part will all start with 0, and the codes in the second part will all start with 1. Recursively apply the steps 3 and 4 to each of the two halves, subdividing groups and adding bits to the codes until each symbol has become a corresponding code leaf on the tree. SHANNON-FANO CODING

79. EXAMPLE PROBLEMS

80. Huffman coding

81. Example problems

82. Lempel-Ziv coding

83. UNIT V SPREAD SPECTRUM AND MULTIPLE ACCESS

84. Multiplexing is the process of simultaneously transmitting two or more individual signals over a single communication channel. due to multiplexing it is possible to increase the number of communication channels so that more information can be transmitted. The typical applications of multiplexing are in telemetry and telephony or in the satellite communication. MULTIPLE ACCESS

85. Basic types of multiplexing. 1] Frequency division multiplexing (FDM) 2] Time division multiplexing (TDM) Types of multiplexing

86. Frequency division multiplexing is a defined as a type of multiplexing where the bandwidth of a single physical medium is divided into a number of smaller, independent frequency channels. Frequency Division Multiplexing

87. FREQUENCY DIVISION MULTIPLE ACCESS (FDMA)

88. Time division multiplexing is a defined as a type of multiplexing where in FDM, instead of sharing a portion of the bandwidth in the form of channels, in TDM, time is shared. Each connection occupies a portion of time in the link. In Time Division Multiplexing, all signals operate with same frequency (bandwidth) at different times. TIME DIVISION MULTIPLE ACCESS (TDMA)

89. CONT…

90. TDMA FRAME TDMA FRAMES

91. CDMA

92. Spread spectrum generally makes use of a sequential  noise -like signal structure to spread the normally  narrowband  information signal over a relatively  wideband  (radio) band of frequencies. The receiver correlates the received signals to retrieve the original information Frequency-hopping spread spectrum  (FHSS),  direct-sequence spread spectrum  (DSSS),  time-hopping spread spectrum  (THSS),  chirp spread spectrum  (CSS), and combinations of these techniques are forms of spread spectrum. The first two of these techniques employ pseudorandom number sequences—created using  pseudorandom number generators —to determine and control the spreading pattern of the signal across the allocated bandwidth. Wireless standard  IEEE 802.11  uses either FHSS or DSSS in its radio interface. n signal.   SPREAD SPECTRUM

93. GENERAL MODEL OF SPREAD SPECTRUM

94. Frequency-hopping spread spectrum  ( FHSS ) is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. The changes are controlled by a code known to both transmitter and  receiver . FHSS is used to avoid interference, to prevent eavesdropping, and to enable code-division multiple access (CDMA) communications FREQUENCY HOPPING SPREAD SPECTRUM (FHSS)

95. FHSS TRANSMITTER

96. FHSS RECEIVER

97. Spread-spectrum  modulation technique primarily used to reduce overall signal interference. The direct-sequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth. After the despreading or removal of the direct-sequence modulation in the receiver, the information bandwidth is restored, while the unintentional and intentional interference is substantially reduced. DIRECT SEQUENCE SPREAD SPECTRUM(DSSS)

98. DSSS TRANSMITTER

99. DSSS RECEIVER