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Unit 2
Modulation And Multiplexing
Subjective questions
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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
• 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 11100000000000 using
one of the following scrambling techniques? Assume that the last nonzero signal level has been positive.
• a. B8ZS
• b. HDB3 (The number of nonzero pules is odd after the last substitution)
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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. 00000000
b. 11111111
c. 01010101
d. 00110011
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18 Draw the graph for the NRZ-I scheme.
a. 00000000
b. 11111111
c. 01010101
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d. 00110011
19. Draw the graph for. Manchester s & differencial manchester cheme.
a. 00000000
b. 11111111
c. 01010101
d. 00110011
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22.differentiate between Statistical & synchronous TDM
23.DIFFERENTIATE between WDM
24.Explain the FDSS technique WITH DIAGRAM
25.Explain the DSSS technique WITH DIAGRAM
1. Unipolar, bipolar, and polar encoding are
types of _______ encoding.
A) Line
B) block
C) NRZ
D) Manchester
• Answer-A
2. _______ encoding has a transition at the
middle of each bit.
A) RZ
B) Manchester
C) Differential Manchester
D) All the above
• Answer-D
3._______ encoding has a transition at the
beginning of each 0 bit.
A) RZ
B) Manchester Differential Manchester
C) All the above
Answer-A
4. PCM is an example of _______ conversion.
A) digital-to-digital
B) digital-to-analog
C) analog-to-analog
D) analog-to-digital
Answer-C
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?
A) 200 samples/s
B) 500 samples/s
C) 1000 samples/s
D) 1200 samples/s
Answer-D
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
7. Which of the following encoding methods
does not provide synchronization?
A) NRZ-L
B) RZ
C) NRZ-I
D) Manchester
Answer-A
8. Which encoding method uses alternating
positive and negative values for 1s?
A) NRZ-I
B) RZ
C) Manchester
D) AMI
Answer-D
10. Block coding can help in _______ at the
receiver.
A) Synchronization
B) Error detection
C) Attenuation
D) (a) and (b)
Answer-D
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
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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
13. In _______ transmission, a start bit and a
stop bit frame IS Sent.
A) asynchronous serial
B) Synchronous serial
C) parallel
D) (a) and (b)
Answer-A
14. In asynchronous transmission, the gap time
between bytes is _______.
A) Fixed
B) variable
C) a function of the data rate
D) Zero
Answer-B
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
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
17. _______ provides redundancy to ensure
synchronization and inherent error detection.
A) Block coding
B) Line coding
C) Scrambling
D) None of the above
Answer-A
18. ________ is normally referred to as mB/nB
coding; it replaces each m-bit group with an nbit group.
A) Block coding
B) Line coding
C) Scrambling
D) None of the above
Answer-A
19. ________ provides synchronization without
increasing the number of bits.
A) Scrambling
B) Line coding
C) Block coding
D) None of the above
Answer-A
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
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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
22. The first step in PCM is ________.
A) Quantization
B) modulation
C) sampling
D) none of the above
Answer-C
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
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
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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
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
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
29. A _________ digital signal includes timing
information in the data being transmitted.
A) self-synchronizing
B) self-modulated
C) self-transmitted
D) none of the above
Answer-A
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
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
32. The signal rate is sometimes called the ____
rate.
A) baud
B) bit
C) signal
D) none of the above
Answer-A
33. The data rate is sometimes called the ___
rate.
A) baud
B) bit
C) signal
D) none of the above
Answer-C
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
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.
A) Polar
B) bipolar
C) unipolar
D) all of the above
Answer-B
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
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37. In ______, the change or lack of change 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-A
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
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
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
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
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42. In Manchester and differential Manchester
encoding, the transition at the middle of the
bit is used for __________.
A) bit transfer
B) baud transfer
C) synchronization
D) none of the above
Answer-C
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
44. In _______encoding, we use three levels:
positive, zero, and negative.
A) unipolar
B) Bipolar
C) polar
D) none of the above
Answer-B
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
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
47. ______ substitutes eight consecutive zeros
with 000VB0VB.
A) B4B8
B) HDB3
C) B8ZS
D) none of the above
Answer-C
48. ______ substitutes four consecutive zeros
with 000V or B00V
A) B4B8
B) HDB3
C) B8ZSf
D) none of the above
Answer-B
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
2. AM and FM are examples of ________
conversion.
A) digital-to-digital
B) digital-to-analog
C) analog-to-analog
D) analog-to-digital
Answer-C
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
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
11. Which of the following is not a digital-toanalog conversion?
A) ASK
B) PSK
C) FSK
D) AM
Answer-D
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
13. In _________, the frequency of the carrier
signal is varied to represent data. Both peak
amplitude and phase remain constant.
A) ASK
B) PSK
C) FSK
D) QAM
Answer-C
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
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
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
17. ________ uses two carriers, one in-phase
and the other quadrature.
A) ASK
B) PSK
C) FSK
D) QAM
Answer-D
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
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
20. Which of the following is not an analog-toanalog conversion?
A) AM
B) PM
C) FM
D) QAM
Answer-D
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
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
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
25. How many carrier frequencies are used in
BASK?
A) 2
B) 1
C) 0
D) none of the above
Answer-B
26. How many carrier frequencies are used in
BFSK?
A) 2
B) 1
C) 0
D) none of the above
Answer-B
27. How many carrier frequencies are used in
BPSK?
A) 2
B) 1
C) 0
D) none of the above
Answer-B
28. How many carrier frequencies are used in
QPSK?
A) 2
B) 1
C) 0
D) none of the above
Answer-A
29. The constellation diagram of BASK has
______ dots.
A) 2
B) 1
C) 0
D) none of the above
Answer-A
30. The constellation diagram of BPSK has
______ dots.
A) 2
B) 1
C) 0
D) none of the above
Answer-A
31. The constellation diagram of QPSK has
______ dots.
A) 2
B) 1
C) 4
D) none of the above
Answer-C
32. The constellation diagram of 16-QAM has
______ dots.
A) 4
B) 16
C) 8
D) none of the above
Answer-B
33. The Federal Communications Commission
(FCC) allows ______kHz for each AM station.
A) 5
B) 10
C) 20
D) none of the above
34. The Federal Communications Commission
(FCC) allows ______ kHz for each FM station.
A) 20
B) 100
C) 200
D) none of the above
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
2. Which multiplexing technique transmits
analog signals?
A) FDM
B) TDM
C) WDM
D) (a) and (c)
Answer-D
3. Which multiplexing technique transmits
digital signals?
A) FDM
B) TDM
C) WDM
D) None of the above
Answer-B
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
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
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
7. Which multiplexing technique involves signals
composed of light beams?
A) FDM
B) TDM
C) WDM
D) none of the above
Answer-C
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
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
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
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
14. FDM is an _________technique.
A) Analog
B) Digital
C) either (a) or (b)
D) none of the above
Answer-A
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
16. ______ is an analog multiplexing technique
to combine optical signals.
A)FDM
B)TDM
C)WDM
D)None of the above
Answer-C
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
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
19. We can divide ____ into two different
schemes: synchronous or statistical.
A)FDM
B)TDM
C)WDM
D)none of the above
Answer-B
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
21. In ________ TDM, slots are dynamically
allocated to improve bandwidth efficiency.
A) Synchronous
B) Statistical
C) Isochronous
D) none of the above
Answer-B
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
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
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

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