SNS COLLEGE OF ENGINEERING
DEPARTMENT OF ECE
DIGITAL COMMUINCATION
MCQ
UNIT I
1. In uniform quantization process
a) The step size remains same
b) Step size varies according to the values of the input signal
c) The quantizer has linear characteristics
d) Both a) and c) are correct
Ans:d
2. The characteristics of compressor in μ-law companding are
a) Continuous in nature
b) Logarithmic in nature
c) Linear in nature
d) Discrete in nature
Ans:a
3. . (001) What is an example of analog-to-digital and digital-to-analog techniques?
a. Amplitude modulation (AM) and frequency modulation (FM).
b. Pulse code modulation (PCM) and frequency shift keying (FSK).
c. Phase modulation (PM) and quadrature phase shift keying (QPSK).
d. Pulse code modulation (PCM) and continuously variable slope delta (CVSD) modulation.
Ans.d
4. (003) The information-carrying components that occur on either side of a carrier are
called
a. sidebands.
b. sine waves.
c. frequency translators.
d. modulating frequencies.
Ans.b
5. (005) The only basic waveform in nature is a
a. carrier wave.
b. pure sine wave.
c. resultant wave.
d. composite wave.
ans.a
6.The last step in Pulse Code Modulation (PCM) is
a.Quantization
b.Sampling
c.Encoding
d.Modulation
ANS :c
C
7. For Pulse Code Modulation (PCM), the quantization error is much greater than
a. decoding
b. Encoding
c. delta modulation
d. multiplexing
ANS: c
8. The modulation techniques used to convert analog signal into digital signal are
a) Pulse code modulation
b) Delta modulation
c) Adaptive delta modulation
d) All of the above
ANS) All of the aboveAnsw
9. The sequence of operations in which PCM is done is
a) Sampling, quantizing, encoding
b) Quantizing, encoding, sampling
c) Quantizing, sampling, encoding
d) None of the above
ANS: a) Sampling, quantizing, encoding
10.One of the disadvantages of PCM is
a) It requires large bandwidth
b) Very high noise
c) Cannot be decoded easily
d) All of the above
ANS a) It requires large bandwidth
11. When the high frequency-------------- with low frequency, it causes Aliasing
A . Interfere
B. Coincide
C. Sampled
ANS:A
12. The rate of sampling to avoid Aliasing
A. fs ≥ 2W
B. fs ≤ 2W
C. fs = 2W
ANS:A
13. Aliasing caused due to
A. Over sampling
B. Under sampling
C. Critical sampling
ANS:B
14. The term Aliasing may be replaced by
A. Overlap
B. Intrusion
C. Mixing
ANS:A
15. Due to aliasing------------ is generated
A. Distortion
B. Twice the message
C. White noise
ANS:A
16.The Conversion Of An Analog Sample Into A Digital Form Is Called The_____________
Process
a. 1.Sampling
2.Symmentric
b. 3.Quantizing
4.Level
17.The Presence Or Absence Of Pulse Is A__________
Code
a. Error
Symbol
4.Encode
18.The Final Operation In The _____________Is To Recover The Analog Signal.
a. 1,Transmitter
2.Receiver
b. 3.Message
3.Path
19.What Are The Parts Of Regenerator ____________,___________,____________
a. 1.Timer,Circuit,Predictor
2.Filter,Circle,Conductor
b. 3.Timer Ckt, Equalizer, Decision Maker
4.Amplifer,Sound,Plexer
20.what is the use of LPF in PCM
1.NOISE increasing
3.noice reducing
2.accuracy
4.none
21.Digitizing the amplitude values is called
•
radiance
•
illuminance
•
sampling
•
quantization
ans:4
22.The process of converting the sample into discrete form is called
1.modulation
2.multiplexing
3.quantisation
4.sampling
Ans:3
23. Your sampling circuit has a 12 bit ADC that samples over a range 1.75 volts. What is the
quantization error in this sampling circuit?
1.450 microvolt
2.427 microvolt
3.437 microvolt
4.457 microvolt
Ans:2
24.quantisatiopn depends on
1.resolution
2.signal level
3.both 1 and 2
4.none
Ans:3
25.example of quantization is
1.round off
2.truncate
3.both 1 and 2
4.Either 1 or 2
Ans:3
UNIT II
1.Predictive constitutes a special form of ____________
a)Detection
b)Correction
c)Interpretation
d)Estimation
Ans: a)Detection
2.The prediction error variance ___________ with increasing predictive order
a)Increase
b)Decrease
c)Remains constant
d)None of these
Ans: b)Decrease
3.In predictor of order one for Rx(0)=___________
a)Rx(2)
b)Rx(0)
c)Rx(1)
d)Rx(X)
Ans: c)Rx(1)
4.Prediction-error process is a __________ process
a)Stationary
b)Linear
c)Desired
d)Predictive
Ans: a)Stationary
5.According to the ____________ filter theory, a predictor is desinged
a)Pass-band
b)Wiener
c)Base-band
d)Reed-Solomon
Ans: b) Wiener
1. Delta modulation transmits--------bits/sample
a.2
b.3
c.1
ANS:c
2. Channel BW is --------- for DM
a. Wide
b. Small
c. Narrow
ANS:b
3. --------------Signal is used in Modulation
a. Analog
b. Digital
ANS:a
4. DM is also known as
a. Linear delta modulator
b. Sigma delta modulator
c. Amplitude delta modulator
ANS:a
5. The updated method of modulation is-----------a. Delta sigma modulator
b. Adaptive delta modulator
c. DPCM
ANS:b
1.lpc is a mathematical operation where future values of_____________are estimated as a linear
samples
a)discrete time signals
b)quantized signals
c)continuous time signals
d)coded signals
ans:a
2.which parameter is used in lpc?
a)sampling rate
b)redundancy coefficient
c)spectral slope
d)encoding
ans:c
3.what is involved to predict the output sequence
a)convolution method
b)allocating spectrum
c)predictor coefficients
d)cyclic codes
ans:c
4.the choice of the predictor depends on the analysis of…
a)frequency
b)bandwidth
c)error
4)spectrum
ans:b
5.voiced signals are given through?
a)impulse generator
b)voice tract
c)power supply
d)regulator
ans:a
UNIT III
1. Bipolar signals are___________
a) Manchester signaling
b) Pseudo Dentary signaling
c) Baseband signaling
Answer: b
2. The power spectral random process varies over a
a) Finite (-1to +1)
b) In finite (–infinity to +infinity)
c) Power spectral range
d) Symbol duration
Answer: a
3. Manchester code is also called as__________
a) Self locking bit code
b) Dc level code
c) Self Clocking code
d) Transition code
Answer: c
4.The time domain pulse for
a)decresed cosine spectrum b)decresed sine spectrum c)raised cosine spectrum d)raised sine
spectrum
ans
C
5. During RZ line codes, _________of signal frequency occurs when 1 is transmitted.
a) Minimum
b) 1/2th
c) Maximum
d) 50%
Answer: c
The ideal standing wave ratio is
A)
1:1
B)
2:1
C)
3:1
D)
0
Ans: a
Which of the following equipment is not required to make receiver sensitivity and noise
measurements?
A)
RF signal generator
B)
frequency counter
C)
spectrum analyzer
D)
dummy load
Ans:c
To determine the noise level when the horizontal spacing on the oscilloscope and the vertical
sensitivity are known, multiply the horizontal spacing by the sensitivity and
A)
multiply by 2
B)
divide by 2
C)
multiply by 3
D)
divide by 3
Ans:b
What is the name of the test that determines whether a cell phone will filter out large nearby
signals that can be mistakenly interpreted as its receiving frequency?
A)
SINAD
B)
quieting
C)
third-order intercept test
D)
cell selectivity test
Ans:c
What is an excellent way to get a nonprecise, quick, qualitative check of a signal?
A)
eye diagram
B)
third-order intercept
C)
SINAD
D)
bit error rate test
Ans:d
A device that produces fixed binary bit patterns in serial form to use as test signals in data
communication systems is a
A)
logic analyzer
B)
function generator
C)
pattern generator
D)
signal generator
Ans:a
An essential oscilloscope like device with a CRT display and built-in microcomputer for fiberoptic work is the
A)
protocol analyzer
B)
spectrum analyzer
C)
logic analyzer
D)
optical time-domain reflectometer
Ans:c
Which of the following is not a common problem in communication equipment?
A)
power supply failures
B)
amplifier failures
C)
cable failures
D)
antenna troubles
Ans:d
A troubleshooting technique where an oscilloscope or other signal detection device to follow a
signal through the various stages of the equipment is called
A)
signal injection
B)
signal tracing
C)
signal analysis
D)
signature
UNIT –IV
1.The Quadrature Amplitude Modulation (QAM) is the combination of
• ASK and FSK
• ASK and PSK
• FSK and PSK
• None of the above
ANS:B
2.Quadrature amplitude modulation is a combination of
• BPSK and PSK
• ASK and BPSK
• ASK and PSK
• BPSK and QPSK
ANS: C
3. QPSK is a modulation scheme where each symbol consists of
a) 4 bits
b) 2 bits
c) 1 bit
d) M number of bits, depending upon the requirement
ANS: b) 2 bits
4. The data rate of QPSK is ___________ of BPSK.
a) Thrice
b) Four times
c) Twice
d) same
ANS: c) Twice
5. QPSK system uses a phase shift of
a) Π
b) Π/2
c) Π/4
d) 2Π
ANS: b) Π/2
1) CONVOLUTION CODES offer an approach to
I)Network coding
II) Source coding
III)Error control coding
IV)cryptographic coding
ans : Error control coding.
2) A state diagram is used to show the relationship between
I)encoder state,input & output
II)decoder state, input & output
III)encoder & decoder state
IV)input & output
Ans: encoder state,input & output
3. Convolutional encoder is a ____________ state machine
I)Finite
II) Infinite
III)constant
IV)stable
4) The performance of a convolutionalcode depends on the
I)coding rate & constraint length
II)SNR ration
III)Encoder & decoder
IV)Baud rate
5) Trellis diagram is an extension of state diagram which explicitly shows the passage of
I) Time
II) Frequency
III) Amplitude
IV) Gain
1. The use of forward- error correcting codes is well suited for channels that can be modeled as
Noise.
a) white- gaussian
b) shot
c) miscellaneous internal
d) thermal
ANS: a) white- gaussian
2. Abbreviate – ARQ
a) Automatic request for retransmission
b) auto recursion for retransmission
c) Automatic retransmission request
d) automatic reverse request
ANS: a) automatic request for retransmission
3. In receiver of an ARQ system, the
is used to perform inverse
Operation.
a) interleaver
b) deinterleaver
c) Inner encoder
d) outer decoder
ANS: b) deinterleaver
4. The
code consists of a finite set of vectors derived from a lattice , to
Which binary information is mapped in a one-to-one fashion.
a) binary
b) error control
c) lattice
d) digital
ANS: c) lattice
5.
is helpful to find out the errors in the received codeword.
a) code
b) binary codes
c) lattice
d) parity
ANS: d) parity
•
The cyclic codes are divided into _______ important classes
•
4
•
5
•
3
•
2
Ans: b) 5
•
Abbreviate CRC codes
•
Cyclic redundancy check
•
Cyclic repeat check
•
Correct redundancy check
•
Costello reed check
Ans: a) Cyclic redundancy check
•
The Reed-Solomon codes are an important subclass of___________BCH codes
•
Binary
•
Digital
•
Non-binary
•
Cyclic
And: c) non-binary
•
The block length of the BCH codes is n=___________
•
(2m -1)
•
(1-2m)
•
(k-1)
•
(1-2k)
Ans: a) (2m-1)
•
One of the most important and powerful classes of the linear block codes are__________
codes
•
BCH
•
CRC
•
Golay
•
Reed-solomon
Ans: a) BCH
1. Non coherent channels emerges when ______, ______ make it impossibleto receive to
perfectly hack the channel state
(a) fast failing , phase route
(b)loping,phase
(c)noise ,frequency
Ans: (a)
2. The system affects sample at _______
(a) particular time
(b)repeatar interval
(c)at an instant
ans : (b)
3.For purely continuousdistribution the MMSE dimension is ______
(a) 1
(b)2
(c) 3
Ans: (a)
4._______ comes under non coherent system
(a) DPSK
(b) PSK
(c) QPU
Ans: (a)
5.Non coherent observations In control systems can similarly arise from _______ and ________
(a)synchronization ,sampling sensor (b) sampling
Ans: (a)
1. How many modes are there in synchronization
a.2
b.3
c.4
ANS: A
2. When coherent detection is used knowledge of both the ………..&…………
a. frequency and phase
b. synchronization and frequency
c. phase and integrator
ANS: A
3. The estimation of performance of symbol is called
a. clock recovery
b. carrier synchronization
c. carrier phase
ANS: A
4. Clock recovery is also called
a. clock synchronization
b. symbol synchronization
c. carrier synchronization
ANS: B
5 .Carrier synchronization is done by how many methods
a.2
b.5
c.3
ANS: C
1.What Are The Types Of Detection
A)Primary, Secondary
B)Coherent ,Non-Coherent
C)Synchronous, Asynchronous
C)Symmetric, Asymmetric
2.___________________ Type Of Detection The Receiver Is Phase Locked To Transmitter.
A)Primary
B)Secondary
C)Coherent
D)Synchronous
3.Non Coherent Is Also Called As___________________ Detection
A)Synchronous
C)Common
B)Envelope
D)Shift
4.Receiver Has Exact Knowledge The_____________ Wave Is Phase Reference
A)Message
B)Input
C)Out Put
D)Carrier
5.Each Of Two Detection Technique Clsses May Be Subdivided Into Binary And ____________
A)M-Array
B)N-Array
C)N-Que
C)M-Ary
1.Differential phase shift keying(DPSK) is a ___________
a.coherent b.non coherent c. linear d.non linear
ans:B
2.DPSK is special case of noncoherent modulation with T=2Tb and E=____
a.2Eb b.3Eb c.4Tb d.6Tb
ans:A
3.In DPSK Encoding scheme is implemented using____________
a.EXOR b.OR c.EXNOR d.NOT
ans:A
4.In DPSK ,The encoded output from logic network is converted to a bipolar using__________
a.upcounter b.down counter c.levelshifter d.levelcounter
ans:C
5.One of the two types of opertions in DPSK are__________
a.differential encoding b.linear coding c.nonlinear d.difference coding
ans:A
1.In DPSK ,The bipolar signal is multipied with carrier using ____________
a.product modulator b.shift key c.phase key d.shift key
ans:A
2.In DPSK to send symbol ___ the phase of current wave is shifted by 180’
a.0 b.1 c.2 d.3
ans:A
3.In DPSK to send symbol ___the phase of current wave is unchanged
a.0 b.1 c.2 d.3
ans:B
4.In DPSK ,The phase difference between waveforms rececived in two successive bit intervals
will be _______________ of ᶱ
a.dependent b.independent c.both d.dependent of onewave
ans:B
5.In DPSK ,The phase difference is based on __________ output
a.uncorrelated b.correlated c.filter d.decision device
ans:B
1 .A binary PSK system is characterized by having a signal space which has
__________dimension and with __________message points
A.ONE AND THREE
B .ONE AND TWO C.TWO AND ONE
ANS:B
2 .A ______________________ system is characterized by having a signal space which has two
dimension and with two message points
A.BINARY FSK
B.QPSK
C.QAM
ANS:A
3 .The signal constellation for QAM consists of a _______lattice of message points
A.SQUARE
B.CUBE
C.SQUARE ROOT
ANS:A
4. The power spectral density of a QPSK signal is
A .No
B .2/No
C. No/2
ANS:C
5. A_________ of signal waveforms that is highly useful for detection of transmitted signals
A.2D VIEW B.3D VIEW C. VECTOR VIEW
ANS:C
1. What is value of number of bit per symbol in FSK?
a.2
b.3
c.4
d.1
ANS:d
2. If symbol is 1 then what is the condition of the random variable?
a.+Sqrt(Eb)
b. -Sqrt(Eb)
c.+ Sqrt(Eb/2)
d.- Sqrt(Eb/2)
ANS:a
3 .What is the average probability of error for non-coherent in BPSK?
a.Pe= 1/2exp(-Eb/4No)
b.Pe= 1/2exp(-Eb/2No)
c.Pe= 1/4exp(-Eb/2No)
d. Pe= 1/2exp(Eb/2No)
ANS:b
4. A signal constellation refers to set of ______________point
a. Carrier
b. intermediate
c. Message
d.received
ANS:c
5. In what degree the decision boundary in signal space diagram for coherent BPSK?
ANS:c
Unit v
a.135
b. 225
c. 45
d. 315
1. Error control for data integrity may be exercised by means of
a) Forward error correction
b) error detection
c) Error correction
d) reverse error correction
ANS: a) Forward error correction
2.The dimensionless ratio r = k/n is called the
a) bit
b)code
c)system
rate.
d) error
ANS: b) code
3.The encoder for a convolutional code operates on the incoming message sequence, using a
a)hamming window
b)blackman window
c) hanning window
d)sliding window
ANS: d) sliding window
4. Abbreviate FEC
a) forward error correction
b)front error correction
c)first error correction
d)final error correction
ANS: a)forward error correction
5.In coding and modulation block diagram noise is given to which channel?
a) encoder
b) source
c)waveform channel
ANS: c) waveform channel
1.------------- has a discrete memory less channel.
a)cyclic codes
b)channel codes
c)convolutional codes
ans:b
2.The rate of channel coding ranges from ----------a)R=C
d) user
b)R≤C
c)R≥C
ans:b
3.In channel coding --------- probability is within the tolerate limits
a)state
b)error
c)cycle
ans:b
4.----------- statement says if R>C, every message will be error
a)positive
b)negative
c)neutral
ans:b
5.what is the channel capacity in the channel coding theorem?
a)minimum
b)maximum
c)constant
ans:b
1.LBC means
a) Linear bit code b) Linear block code c)Linear block check d)Linear binary code
Answer: Linear block code
2. The generator matrix G is used in the encoding operation at
a) Receiver b) Transmitter c) Encoder d) Decoder
Answer: transmitter
3. The syndrome depends only
a) Transmitted code word b) Error pattern c) Receive code word d) Parity pattern
Answer: Error pattern
4. Minimum distance of the LBC is defined as
a) Smallest distance b) Longest distance c) Medium distance
Answer: Smallest
5. Error detection
a)dmin≤s+1 b)dmin≥s+1 c)dmax≥s+1
ans:b
•
The combination of the modulator the waveform channel and the detector acts as
_______________
•
Discrete memoryless channel
•
Memoryless channel
•
Discrete channel
•
None of the above
Ans: a) discrete memoryless channel
•
Demodulate output is indicated by the symbol _______
•
I
•
J
•
K
•
L
Ans: b) j
•
Abbreviate BSC
•
Binary symmetric channel
•
Bit symmetric channel
•
Binary schematic channel
•
Binary symmetric code
Ans: a) Binary symmetric channel
•
Channel coding theorem is ______ in nature
•
Constructive
•
Non-constructive
•
Consecutive
•
Non-consecutive
Ans: b) Non-constructive
•
Channel coding theorem only asserts the existence of _____
•
Good codes
•
Moderate codes
•
Parity bits
•
Code word
Ans: a) good codes
1)
IN VITERBI DECODING HOW MANY ERROR SHOULD WANT TO BE OCCURRED
•
1
•
5
•
4
•
2
ANS : 1
•
THE VITERBI ALGORITM IS A _____________DECODE
•
MAXIMUM –LIKEHOOD
•
MINIMUM –LIKEHOOD
•
NONE OF THESE
ANS:1
3) THE VITERBI ALGORITHM WAS EQUIVALENT TO TECHNIQUE KNOWN
HAS_______________
•
PROGRAM
•
DYNAMIC
•
DYNAMIC PROGRM
•
ALL THE ABOVE
ANS: C
5) THE PATHS THAT ARE RETAINED BY THE ALGORITHM ARE______
1.
SURVIVORS
2.
LENGTH
3.
HEIGHT
4.
NONE OF THE ABOVE
ANS:1
4) IN ________YEAR VITERBI PROPOSED A DECODING ALGORITHM FOR
CONVOLUCTION CODES
•
1947
•
1996
•
1945
•
1967
ANS:4
1. . For hamming distance dmin and number of errors D, the condition for receiving invalid
codeword is
a) D <= dmin + 1
b) D <= dmin-1
c) D <= 1- dmin
d) D <= dmin
ANSWER: b) D <= dmin-1
2. Q2. For hamming distance dmin and t errors in the received word, the condition to be able to
correct the errors is
a) 2t + 1 <= dmin
b) 2t + 2 <= dmin
c) Both a) and b)
d) 2t + 1<= 2dmin
ANSWER: c) Both a) and b)
3.consider X=1010101 Y=1101111
Find the hamming distance
a)5
b)1
c)2
d)4
ANSWER:d) 4
4.what is the hamming weight?
For X= 1011101
a)4
b)5
c)1
d)7
Answer:(b)5
5.find the dmin of the code vectors
X1=1010101
X2=110001
X3=111011
a)1
b)2
c)6
d)3
ans:d)3