1. Unit 2 Modulation And Multiplexing

2. Subjective questions
1. List three techniques of digital-to-digital conversion.
2. Distinguish between a signal element and a data element.
3. Distinguish between data rate and signal rate.
4. Define baseline wandering and its effect on digital transmission.
5. Define a DC component and its effect on digital transmission.
6. Define the characteristics of a self-synchronizing signal.
Compare and contrast PCM and DM.
11. What are the differences between parallel and serial transmission?
12. List three different techniques in serial transmission and explain the differences.
13.Which characteristics of an analog signal are changed to represent the digital signal in each of the following digital-to-analog conversion?
a. ASK
b. FSK
c. PSK
d. QAM

3. 14.The input stream to a 4B/5B block encoder is 0100 0000 0000 0000 0000 OOOI.
Answer the following questions:
a. What is the output stream?
b. What is the length of the longest consecutive sequence of Os in the input?
c. What is the length of the longest consecutive sequence of Os in the output?
15. How many invalid (unused) code sequences can we have in 5B/6B encoding? How many in 3B/4B encoding?
16. What is the result of scrambling the sequence using one of the following scrambling techniques? Assume that the last non-zero signal level has been positive.
a. B8ZS
b. HDB3 (The number of nonzero pules is odd after the last substitution)

4. 17.Draw the graph of the NRZ-L scheme using each of the following data streams, assuming that the last signa11evel has been positive. From the graphs, guess the bandwidth for this scheme using the average number of changes in the signal level.
a b c d
18 Draw the graph for the NRZ-I scheme.
19. Draw the graph for. Manchester s & differencial manchester cheme.

5. 22.differentiate between Statistical & synchronous TDM
23.DIFFERENTIATE between WDM
24.Explain the FDSS technique WITH DIAGRAM
25.Explain the DSSS technique WITH DIAGRAM

6. 1. Unipolar, bipolar, and polar encoding are types of _______ encoding.
A) Line
B) block
C) NRZ
D) Manchester
Answer-A

7. 2. _______ encoding has a transition at the middle of each bit.
A) RZ
B) Manchester
C) Differential Manchester
D) All the above
Answer-D

8. 3._______ encoding has a transition at the beginning of each 0 bit.RZ
Manchester Differential Manchester
C) All the above
Answer-A

9. 4. PCM is an example of _______ conversion.
digital-to-digital
digital-to-analog
C) analog-to-analog
D) analog-to-digital
Answer-C

10. 5. If the frequency spectrum of a signal has a bandwidth of 500 Hz with the highest frequency at 600 Hz, what should be the sampling rate, according to the Nyquist theorem?
200 samples/s
500 samples/s
1000 samples/s
1200 samples/s
Answer-D

11. 6. The Nyquist theorem specifies the minimum sampling rate to be_______.
A) equal to the lowest frequency of a signal
B) equal to the highest frequency of a signal
C) twice the bandwidth of a signal
D) twice the highest frequency of a signal
Answer-D

12. 7. Which of the following encoding methods does not provide synchronization?
A) NRZ-L
B) RZ
C) NRZ-I
D) Manchester
Answer-A

13. 8. Which encoding method uses alternating positive and negative values for 1s?
NRZ-I RZ
C) Manchester
D) AMI
Answer-D

14. 10. Block coding can help in _______ at the receiver.
A) Synchronization
B) Error detection
C) Attenuation
D) (a) and (b)
Answer-D

15. 11.In _______ transmission, bits are transmitted simultaneously, each across its own wire.
A) Asynchronous serial
B) Synchronous serial
C) Parallel
D) (a) and (b)
Answer-C

16. 12. In _______ transmission, bits are transmitted over a single wire, one at a time.
A) asynchronous serial
B) synchronous serial
C) Parallel
D) (a) and (b)
Answer-D

17. 13. In _______ transmission, a start bit and a stop bit frame IS Sent.
asynchronous serial
Synchronous serial
C) parallel
D) (a) and (b)
Answer-A

18. 14. In asynchronous transmission, the gap time between bytes is _______.
Fixed
variable
C) a function of the data rate
D) Zero
Answer-B

19. 15.___________ conversion involves three techniques: line coding, block coding, and scrambling.
A) Analog-to-digital
B) Digital-to-analog
C) Analog-to-analog
D) Digital-to-digital
Answer-D

20. 16. ________ is the process of converting digital data to a digital signal.
A) Block coding
B) Line coding
C) Scrambling
D) ALL of the above
Answer-D

21. 17. _______ provides redundancy to ensure synchronization and inherent error detection.
Block coding
Line coding
C) Scrambling
D) None of the above
Answer-A

22. 18. ________ is normally referred to as mB/nB coding; it replaces each m-bit group with an n-bit group.
A) Block coding
B) Line coding
C) Scrambling
D) None of the above
Answer-A

23. 19. ________ provides synchronization without increasing the number of bits.
A) Scrambling
B) Line coding
C) Block coding
D) None of the above
Answer-A

24. 20. Two common scrambling techniques are ________.
A) NRZ and RZ
B) AMI and NRZ
C) B8ZS and HDB3
D) Manchester and differential Manchester
Answer-C

25. 21. The most common technique to change an analog signal to digital data is called __________.
A) PAL
B) PCM
C) sampling
D) none of the above
Answer-B

26. 22. The first step in PCM is ________.
Quantization
modulation
C) sampling
D) none of the above
Answer-C

27. 23. There are three sampling methods: __________.
A) quantized, sampled, and ideal
B) ideal, sampled, and flat-top
C) ideal, natural, and flat-top
D) none of the above
Answer-C

28. 25 .While there is (are) only _____ way(s) to send parallel data, there is (are) ______subclass(es) of serial transmission.
A) one; two
B) two; three
C) one; three
D) none of the above
Answer-B

29. 26. In ______ transmission, we send 1 start bit (0) at the beginning and 1 or more stop bits (1s) at the end of each byte.
A) Synchronous
B) Asynchronous
C) isochronous
D) none of the above
Answer-B

30. 27. In _________ transmission, we send bits one after another without start or stop bits or gaps. It is the responsibility of the receiver to group the bits.
A) synchronous
B) asynchronous
C) isochronous
D) none of the above
Answer-A

31. 28.The ________ mode provides synchronization for the entire stream of bits must. In other words, it guarantees that the data arrive at a fixed rate.
A) synchronous
B) asynchronous
C) isochronous
D) none of the above
Answer-A

32. 29. A _________ digital signal includes timing information in the data being transmitted.
self-synchronizing
self-modulated
C) self-transmitted
D) none of the above
Answer-A

33. 30. In decoding a digital signal, the receiver calculates a running average of the received signal power, called the _______.
A) baseline
B) base
C) Line
D) none of the above

34. 31. The ________ rate defines the number of data elements sent in 1s; the ______ rate is the number of signal elements sent in 1s.
A) data; signal
B) signal; data
C) baud; bit
D) none of the above
Answer-A

35. 32. The signal rate is sometimes called the ____ rate.
A) baud
B) bit
C) signal
D) none of the above
Answer-A

36. 33. The data rate is sometimes called the ___ rate.
A) baud
B) bit
C) signal
D) none of the above
Answer-C

37. 34. In a _____ scheme, all the signal levels are on one side of the time axis, either above or below.
A) polar
B) bipolar
C) Unipolar
D) all of the above
Answer-A

38. 35. In ______ schemes, the voltages are on the both sides of the time axis. For example, the voltage level for 0 can be positive and the voltage level for 1 can be negative.
Polar
bipolar
C) unipolar
D) all of the above
Answer-B

39. 36. In _____, the level of the voltage determines the value of the bit.
A) NRZ-I
B) NRZ-L
C) both (a) and (b)
D) neither (a) nor (b)
Answer-B

40. 37. In ______, the change or lack of change in the level of the voltage determines the value of the bit.
NRZ-I
NRZ-L
C) both (a) and (b)
D) neither (a) nor (b)
Answer-A

41. 38. The idea of RZ and the idea of NRZ-L are combined into the ________ scheme.
A) Manchester
B) differential Manchester
C) both (a) and (b)
D) neither (a) nor (b)
Answer-A

42. 39. The idea of RZ and the idea of NRZ-I are combined into the ________ scheme.
A) Manchester
B) differential Manchester
C) both (a) and (b)
D) neither (a) nor (b)
Answer-B

43. 40. In _______ encoding, the duration of the bit is divided into two halves. The voltage remains at one level during the first half and moves to the other level in the second half. The transition at the middle of the bit provides synchronization.
A) Manchester
B) differential Manchester
C) both (a) and (b)
D) neither (a) nor (b)
Answer-A

44. 41. In ___________ there is always a transition at the middle of the bit, but the bit values are determined at the beginning of the bit. If the next bit is 0, there is a transition; if the next bit is 1, there is none.
A) Manchester
B) differential Manchester
C) both (a) and (b)
D) neither (a) nor (b)
Answer-B

45. 42. In Manchester and differential Manchester encoding, the transition at the middle of the bit is used for __________.
bit transfer
baud transfer
synchronization
D) none of the above
Answer-C

46. 43. The minimum bandwidth of Manchester and differential Manchester is ____ that of NRZ.
A) the same as
B) twice
C) thrice
D) none of the above
Answer-B

47. 44. In _______encoding, we use three levels: positive, zero, and negative.
A) unipolar
B) Bipolar
C) polar
D) none of the above
Answer-B

48. 45. The _____ scheme uses data patterns of size 2 and encodes the 2-bit patterns as one signal element belonging to a four-level signal.
A) 4B5B
B) 2B1Q
C) MLT-3
D) none of the above
Answer-B

49. 46. The ______ scheme uses three levels (+V, 0, and -V) and three transition rules to move between the levels.
A) 4B5B
B) 2B1Q
C) MLT-3
D) none of the above
Answer-C

50. 47. ______ substitutes eight consecutive zeros with 000VB0VB.
A) B4B8
B) HDB3
C) B8ZS
D) none of the above
Answer-C

51. 48. ______ substitutes four consecutive zeros with 000V or B00V
B4B8
HDB3
C) B8ZSf
D) none of the above
Answer-B

53. 1. ASK, PSK, FSK, and QAM are examples of ________ conversion.
A) digital-to-digital
B) digital-to-analog
C) analog-to-analog
D) analog-to-digital
Answer-B

54. 2. AM and FM are examples of ________ conversion.
digital-to-digital
digital-to-analog
C) analog-to-analog
D) analog-to-digital
Answer-C

55. 3. In QAM, both ________ of a carrier frequency are varied.
A) frequency and amplitude
B) phase and frequency
C) amplitude and phase
D) none of the above
Answer-C

56. 10. _______ conversion is the process of changing one of the characteristics of an analog signal based on the information in the digital data.
A) Digital-to-analog
B) Analog-to-analog
C) Analog-to-digital
D) Digital-to-digital
Answer-A

57. 11. Which of the following is not a digital-to-analog conversion?
A) ASK
B) PSK
C) FSK
D) AM
Answer-D

58. 12. In ________, the amplitude of the carrier signal is varied to create signal elements. Both frequency and phase remain constant.
A) ASK
B) PSK
C) FSK
D) QAM
Answer-A

59. 13. In _________, the frequency of the carrier signal is varied to represent data. Both peak amplitude and phase remain constant.
ASK
PSK
C) FSK
D) QAM
Answer-C

60. 14. In ________, the phase of the carrier is varied to represent two or more different signal elements. Both peak amplitude and frequency remain constant.
A) ASK
B) PSK
C) FSK
D) QAM
Answer-B

61. 15. A constellation diagram shows us the __________ of a signal element, particularly when we are using two carriers (one in-phase and one quadrature).
A) amplitude and phase
B) amplitude and frequency
C) frequency and phase
D) none of the above
Answer-A

62. 16. Quadrature amplitude modulation (QAM) is a combination of ___________.
A) ASK and FSK
B) ASK and PSK
C) PSK and FSK
D) none of the above
Answer-B

63. 17. ________ uses two carriers, one in-phase and the other quadrature.
A) ASK
B) PSK
C) FSK
D) QAM
Answer-D

64. 18. _________ conversion is the representation of analog information by an analog signal.
A) Digital-to-analog
B) Analog-to-analog
C) Analog-to-digital
D) Digital-to-digital
Answer-B

65. 19. Analog-to-analog conversion is needed if the available bandwidth is _______.
A) low-pass
B) band-pass
C) either (a) or (b)
D) neither (a) nor (b)
Answer-B

66. 20. Which of the following is not an analog-to-analog conversion?
A) AM
B) PM
C) FM
D) QAM
Answer-D

67. 21. In _____ transmission, the carrier signal is modulated so that its amplitude varies with the changing amplitudes of the modulating signal.
A) AM
B) PM
C) FM
D) none of the above
Answer-A

68. 22. In _____ transmission, the frequency of the carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signal. The peak amplitude and phase of the carrier signal remain constant, but as the amplitude of the information signal changes, the frequency of the carrier changes correspondingly.
A) AM
B) PM
C) FM
D) none of the above
Answer-C

69. 23. In _____ transmission, the phase of the carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signal.
A) AM
B) PM
C) FM
D) none of the above
Answer-B

70. 25. How many carrier frequencies are used in BASK?
D) none of the above
Answer-B

71. 26. How many carrier frequencies are used in BFSK?
D) none of the above
Answer-B

72. 27. How many carrier frequencies are used in BPSK?
D) none of the above
Answer-B

73. 28. How many carrier frequencies are used in QPSK?1
C) 0
D) none of the above
Answer-A

74. 29. The constellation diagram of BASK has ______ dots.
D) none of the above
Answer-A

75. 30. The constellation diagram of BPSK has ______ dots.2 1
C) 0
D) none of the above
Answer-A

76. 31. The constellation diagram of QPSK has ______ dots.
B) 1
C) 4
D) none of the above
Answer-C

77. 32. The constellation diagram of 16-QAM has ______ dots.
B) 16
C) 8
D) none of the above
Answer-B

78. 33. The Federal Communications Commission (FCC) allows ______kHz for each AM station.
B) 10
C) 20
D) none of the above

79. 34. The Federal Communications Commission (FCC) allows ______ kHz for each FM station.
B) 100
C) 200
D) none of the above

81. 1. The sharing of a medium and its link by two or more devices is called _______.
A) Modulation
B) Encoding
C) line discipline
D) Multiplexing
Answer-D

82. 2. Which multiplexing technique transmits analog signals?
A) FDM
B) TDM
C) WDM
D) (a) and (c)
Answer-D

83. 3. Which multiplexing technique transmits digital signals?
A) FDM
B) TDM
C) WDM
D) None of the above
Answer-B

84. 4. Which multiplexing technique shifts each signal to a different carrier frequency?
A) FDM
B) TDM
C) Both (a) and (b)
D) None of the above
Answer-D

85. 5. In synchronous TDM, for n signal sources of the same data rate, each frame contains _______ slots. A) N B) n + 1 C)n – 1 D) 0 to n Answer-A

86. 6. In TDM, the transmission rate of the multiplexed path is usually _______ the sum of the transmission rates of the signal sources.
A) greater than
B) less than
C) equal to
D) not related to
Answer-A

87. 7. Which multiplexing technique involves signals composed of light beams?
A) FDM
B) TDM
C) WDM
D) none of the above
Answer-C

88. 8. _________ utilization is the use of available bandwidth to achieve specific goals. A)Frequency B)Bandwidth C)Amplitude D)None of the above Answer-B

89. 9. ________ can be achieved by using multiplexing; ______ can be achieved by using spreading. A) Efficiency; privacy and antijamming B) Privacy and antijamming; efficiency C)Privacy and efficiency; antijamming D) Efficiency and antijamming; privacy Answer-A

90. 10. In a multiplexed system, ____ lines share the bandwidth of ____ link. A) 1; n B) 1; 1 C) n; 1 D) n; n Answer-C

91. 13. ______ can be applied when the bandwidth of a link (in hertz) is greater than the combined bandwidths of the signals to be transmitted. A) TDM B) FDM C) Both (a) or (b) D) Neither (a) or (b) Answer-B

92. 14. FDM is an _________technique
14. FDM is an _________technique. A) Analog B) Digital C) either (a) or (b) D) none of the above Answer-A

93. 15. ____ is designed to use the high bandwidth capability of fiber-optic cable. A) FDM B) TDM C) WDM D) None of the above Answer-C

94. 16. ______ is an analog multiplexing technique to combine optical signals. A)FDM B)TDM C)WDM D)None of the above Answer-C

95. 17. _____ is a digital process that allows several connections to share the high bandwidth of a link. A)FDM B)TDM C)WDM D)None of the above Answer-B

96. 18. _____ is a digital multiplexing technique for combining several low-rate channels into one high-rate one. A)FDM B)TDM C)WDM D)None of the above Answer-B

97. 19. We can divide ____ into two different schemes: synchronous or statistical. A)FDM B)TDM C)WDM D)none of the above Answer-B

98. 20. In ________ TDM, each input connection has an allotment in the output even if it is not sending data. A) Synchronous B) Statistical C) Isochronous D) none of the above Answer-A

99. 21. In ________ TDM, slots are dynamically allocated to improve bandwidth efficiency. A) Synchronous B) Statistical C) Isochronous D) none of the above Answer-B

100. 22. In ________, we combine signals from different sources to fit into a larger bandwidth. A) spread spectrum B) line coding C) block coding D) none of the above Answer-D

101. 23. _______ is designed to be used in wireless applications in which stations must be able to share the medium without interception by an eavesdropper and without being subject to jamming from a malicious intruder. A) Spread spectrum B) Multiplexing C) Modulation D) None of the above. Answer-A

102. 25. The ______ technique expands the bandwidth of a signal by replacing each data bit with n bits. A)FDM B)DSSS C)FHSS D)TDM Answer-B