module-4 - nptel.vtu.ac.innptel.vtu.ac.in/vtu-nmeict/digicomm/module4.pdf · 36 explain why in...
TRANSCRIPT
Module-4
Session wise Topics
Digital Modulation Techniques (Part - 7)
Digital Modulation Techniques (part - 8)
Digital Modulation Techniques (Part - 9)
Digital Modulation Techniques (Part - 10)
Probability of Error Calculation
Calculation of Probability of Error
Calculation of Probability of Error
Equalizers
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4.1: NPTEL Video Link
Module-4: Video Lecture number 18 to 25 Sl.
No. Module
No. Lecture
No. Topics covered Video Link
1 Mod 04 Lec-18 FSK scheme.Orthogonal FSK Pulse Position Modulation
http://nptel.ac.in/courses/117101051/18
2 Mod 04 Lec-19 Biorthogonal Signals http://nptel.ac.in/courses/117101051/19
3 Mod 04 Lec-20 Memory less modulation scheme http://nptel.ac.in/courses/117101051/20
4 Mod 04 Lec-21 Eye diagram http://nptel.ac.in/courses/117101051/21
5 Mod 04 Lec-22 Probability of Error http://nptel.ac.in/courses/117101051/22
6 Mod 04 Lec-23 Probability of Error http://nptel.ac.in/courses/117101051/23
7 Mod 04 Lec-24 Probability of Error http://nptel.ac.in/courses/117101051/24
8 Mod 04 Lec-25 Equalizers http://nptel.ac.in/courses/117101051/25
NPTEL Web Link: http://nptel.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Digi%20Comm/New_index1.html
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4.2) Questions:
Questions from Video Lectures of NPTEL
Sl no Questions Video
Number
Time in
Minutes
1 Derive the orthonormal vectors for the two vectors f(t) and g(t) given below:
18 4 - 12
2 Define FSK. Write the pass band representation and complex form of
representation using low pass equivalent signal.
18 13
3 What are the possible values of f in FSK? 18 16
4 Find the inner product of two signals xm(t) and xn(t) in FSK. Plot for the
different values of m and n.
18 17
5 Draw the orthogonal FSK constellation for M=3 with three orthonormal basis
functions.
18 27
6 For a two dimensional signal set, write the constellation of FSK. 18 32
7 What are the properties of orthogonal FSK? 18 33
8 Define Pulse Position Modulation. 18 40
9 Explain the PPM technique with waveforms for the time shifting constant, t
= T/4.
18 42
10 Compare the properties of orthogonal FSK and PPM modulation techniques. 18 46
11 Describe the Bi-orthogonal signals for a set of N-orthogonal signals. 19 3
12 Draw the signal space diagrams for N=2 and N=3 signals. 19 6
13 What are the properties of Bi-orthogonal signals? 19 8
14 Explain the principle of demodulation in bi-orthogonal scheme. 19 13-21
15 Describe how the transmitted signal is estimated using the distance metric
from the received signal vector?
19 24
16 How the N-complex signals are transmitted in 2N dimension considering them
as real signals.
19 28
17 Describe the process of demodulation in bi-orthogonal scheme using
correlation receiver.
19 33-39
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18 Describe the matched filter implementation for the demodulation of bi-
orthogonal scheme.
19 42
19 Compare the correlation receiver implementation and matched filter
implementation for Bi-orthogonal schemes.
19 45
20 Derive the matched filter receiver structure in which each signal is matched to
the signal.
19 48
21 Explain the working of receiver using M-matched filter matched directly to
the signal.
20 4
22 With constellation diagram explain the demodulation of PSK signal 20 7
23 With constellation diagram explain the demodulation of 16-QAM signal. 20 11
24 How an FSK signal can be detected using orthogonal signal set. 20 15
25 Explain the detection procedure for Biorthogonal signals 20 17
26 What is equivalence signal set? What is its signification? 20 18
27 With suitable example explain the process of signal translation. 20 20
28 What is the advantage of signal translation? Explain with an example. 20 23
29 Briefly discuss the need of signal rotation in higher modulation scheme. 20 28
30 Explain how a two dimensional FSK signal can be translated and rotated into
one dimension signal set?
20 31
31 Explain how a three dimensional FSK signal can be translated and rotated into
two dimension signal set?
20 32
32 How to choose best transition point in case of signal transition? 20 33
33 What is simplex signal set? Explain with an example. 20 42
34 What are the properties of simplex signal set? Explain with suitable examples. 20 45
35 Explain the effect of channel and receiver on transmitted pulse signal. 21 3
36 Explain why in practice zero ISI is not possible? 21 5
37 Explain the significance of eye diagram to observe ISI 21 10
38 Write the eye diagram for a binary PAM signal and show the optimum
sampling time.
21 12
39 Explain how noise immunity can be calculated in an eye diagram. 21 17
40 Explain how sampling error immunity can be indicated in an eye diagram. 21 19
41 Write the eye diagram for a 4- PAM signal 21 20
42 Explain the working of communication system with channel being continuous
and signal transmitted is discrete.
21 26
43 Briefly discuss the function performed by real time vector discrete-time 21 30
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channel
44 What is discrete memoryless channel? Explain its operation. 21 33
45 For M-ary signal write the channel probability transition diagram. 21 36
46 Explain how discrete memory less channel and real vector discrete time
channel are relevant channel models even for continuous time channels.
21 36
47 What is the function performed by the mapper in communication system?
Explain with an example.
21 38
48 What is the advantage of using gray coding while mapping the signals?
Explain how gray coding can be assigned to:
(i) 8-PSK system (ii) 16-QAM system.
21 41
49 What are the criteria’s we should use for designing a mapper? 21 47
50 Explain the trade-off between bandwidth, average energy, bit rate and
probability of error in communication.
21 53
51 With neat diagram explain the working of Matched filter receiver. 22 07
52 What is the function performed by weighting matrix in Matched filter receiver 22 08
53 For a zero mean additive white Gaussian noise with variance N0/2 find the
power spectral density,
22 11
54 Define co-variance of two noise components.ni and nj and derive an
expression for the same.
22 19
55 For 4-PSK write the received signal vector and comment on the effect of noise
on the received vector.
22 29
56 Explain the decision procedure for 4-PSK received signals. 22 30
57 Derive an expression for probability of error for binary PAM. 22 31
58 Define Q-function and what is its significance in finding the probability of
error in communication?
22 37
59 Prove that the Q-function ( ) < / 22 47
60 Explain the procedure to simulate communication using binary PAM through
AWGN discrete-time channel.
22 48
61 Derive an expression for probability of error for any orthogonal signal set. 23 05
62 Derive an expression for probability of error for noise variation in one
dimension only.
23 07
63 Obtain an expression for probability of error for noise variation in two
dimensions only.
23 13
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64 Derive an expression for probability of error for noise variation in three
dimensions only.
23 16
65 Obtain an expression for probability of error for noise variation in four
dimensions only.
23 19
66 Write the signal space representation of 16-QAM and derive an expression for
probability of error in case of 16-QAM.
23 22
67 Derive an expression for probability of error for orthogonal signals. 23 40
68 Obtain an expression for probability of error for Bi-orthogonal signals. 24 03
69 Explain the detection rule in case of Bi-orthogonal signals. 24 06
70 What is union Bound on the probability of error? Derive an expression for the
same.
24 16
71 Derive an expression for union bound for orthogonal signal set. 24 20
72 Derive an expression for union bound for Biorthogonal signal set. 24 23
73 What is meaning of modulation with memory, explain with suitable example. 24 33
74 What is baseband modulation? 24 33
75 What are RZ and NRZ representation of binary signals? 24 34
76 Represent binary data 10110001 using NRZ line code without memory. 24 35
77 Represent binary data 10110001 using NRZI line code with memory. 24 36
78 What is differential encoding? What is its significance in modulation? 24 38
79 Explain the working of differential PSK [DPSK] and briefly discuss that DPSK is
a modulation with memory type.
24 43
80 With neat receiver block diagram explain the working of DPSK demodulation
scheme
24 47
81 What is an equalizer? What are the functions performed by an equalizer? 25 03
82 Briefly discuss the criterion for no ISI. 25 05
83 What is ISI? Obtain an expression for ISI at the receiver. 25 09
84 Write the equivalent model of the channel. 25 13
85 What is linear equalizer? Explain its operation. 25 15
86 Explain the function of peak distortion criterion equalizer. 25 19
87 What are the disadvantages of peak distortion equalizer? 25 23
88 Explain the working of MSE criterion equalizer. 25 28
89 Explain the operation of decision feedback equalizer. 25 30
90 What is adaptive equalizer? Explain its role in communication. 25 41
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4.3) Quiz Questions
Questions: Fill in the blanks.
Q.
No.
Question Answer
1 All the signals in the orthogonal FSK are __________ to each other. Orthogonal.
2 In orthogonal FSK signal set, the energy of all the signals is _____. same
3 The number of points is ____ to the number of dimension in orthogonal FSK
scheme.
Equal
4 The bandwidth of the FSK signal ______ proportional to the number of
signals in the orthogonal FSK scheme.
Increases.
5 The minimum distance between all pairs of points in FSK is __________. Same.
6 In PPM scheme the pulses are shifted in _________. Time
7 The different pulses used in the PPM scheme are _______ to each other. orthogonal
8 In PPM, Bandwidth increases as the number of points are __________. Increased.
9 FSK and PPM are ______ to each other. Dual
10 Both the orthogonal FSK and PPM schemes have same _____________. Properties
11 In bi-orthogonal scheme as the dimension is increased the bandwidth
requirement __________.
Increases.
12 For PAM we need ______ matched filter for demodulation one
13 There are ______kinds of decision region shapes for 16-QAM reception Three
14 The signal are said to be _________ if the probability of error will not
change either by rotation or translation.
Equivalent
15 During signal transition we choose the signal set which has________
average energy.
Minimum
16 The energy of simplex signal set is __________ original orthogonal signal
set.
Less than
17 The inner product of any pair of simplex signal set is_____ Constant
18 __________ is graphical illustration of ISI. Eye diagram
19 If ISI is present in a channel then we refer it as discrete ________ channel. memory
20 In 16-QAM gray code the difference between adjacent point is ___ bit one
21 The criteria we use for designing a mapper is to give _______ probability of
error
Minimum
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22 If the distance between the points increases then the probability of error
_______
decreases
23 If the receiver design is not optimum then probability of error will ________ Increases
24 If the input noise to matched filter is Gaussian then the output noise is
_________
Gaussian
25 The Q-function in terms of cumulative distribution function is Q(x)=_______ Q(x)=1-Fz(x)
26 In case of modulation with memory the current transmitting signal depends
________ transmitted signal also.
Previous
27 The three basic digital modulation schemes are ________ ________ and
______.
ASK, PSK
and FSK
28 In binary PSK the two signals transmitted are called _________ signals. Antipodal
29 Generally in binary FSK the two signals transmitted are ________ signals. Orthogonal
30 The number basis signals required in QPSK scheme is ________. Two
31 For a specified average transmitted power, the system that gives the lowest
probability of error is ______.
PSK
32 For the same bit error and channel noise, the Pe of QPSK is the same as that
of __________.
Binary PSK
33 Spectral efficiency is the ratio of _______ to ______.
Bit
rate/Bandwidth.
34 To reduce the effect of channel noise at receiver we use________ Equalizer
35 In an ideal Nyquist channel of bandwidth of W we can transmit without ISI
at a maximum rate of _________
2W
36 In an eye pattern the maximum opening of eye in the vertical direction
indicates __________
Noise margin
37 The peak distortion equalizer is also referred as ________ equalizer Zero forcing
38 The compensator for ISI is __________ An Equalizer.
39 In a non-ideal channel of bandwidth, W the signal transmission at a symbol
rate exceeding W results in ______.
ISI
40 Two types of linear equalizers used in practical implementation are ___ and
____ equalizers.
Base band and
Pass band.
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4.4) True or False:
Q: State whether the following statements are True or False?
Answer 1 FSK signal set is orthogonal if f = k/2T, where k is an integer. T
2 Orthogonal FSK is a constant energy modulation scheme. T
3 The number of points is same as the dimension of the signal space in orthogonal FSK. T
4 In orthogonal FSK, the Bandwidth remains constant when the number of points is
increased.
F
5 The energy of the signal can be constant while increasing the number of points in
orthogonal FSK.
T
6 In PPM method the information is present in the position of the pulse. T
7 In pulse position modulation scheme the information is transmitted by transmitted
the base band pulse at different time instants
T
8 PSK and FSK are constant energy schemes T
9 PAM and QAM are constant energy schemes. F
10 FSK and PPM are orthogonal signaling schemes. T
11 All the signals in Bi-orthogonal signals have constant energy. T
12 Distances between the points in constellation of bi-orthogonal signals are not
uniform.
T
13 QAM technique can be considered as combination of PAM and PSK techniques. T
14 FSK is a nonlinear modulation scheme. T
15 The performance of correlation receiver and matched filter are not same. F
16 The performance of matched filter receiver using N-filters and M-filters are not same,
where M is the number of signals transmitted and N is the number of basis functions
used.
F
17 Bi-orthogonal schemes can be used with FSK. T
18 Bi-orthogonal scheme cannot be used with PPM. F
19 The signal constellation points of a bi-orthogonal scheme for M=4 are (1,0), (-1,0),
(0,1) and (0, -1).
T
20 The signal constellation points of a bi-orthogonal scheme for M=4 are (1,0), (-1,0), F
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(1,1) and (1, -1).
21 For QAM demodulator a minimum of two matched filters are used. T
22 For any orthogonal signal set the number of points is same as the dimension of the
signal space,
T
23 For any orthogonal modulation technique the energy of each signal is different. F
24 A good signaling scheme is the one, which gives less probability of error for maximum
energy reception.
F
25 By signal translation we can reduce the average transmission energy of the signal. T
26 By signal translation we can maintain the same probability of error. T
27 By signal rotation the probability of error will change. F
28 One dimensional signal will take less bandwidth compare to two dimensional signals. T
29 We can translate and rotate three dimensional FSK signal into two dimension signal
set
T
30 In signal transition all transition point will have same average energy. F
31 The inner product of simplex signal set is zero. F
32 After signal translation distance between any pair points remains same. T
33 In practice zero ISI is not possible. T
34 It may be expensive to implement pulse p(t) and receiver filter a(t) to avoid ISI
completely.
T
35 In wireless channel the channel behavior is changing. T
36 Detector will pick-up the point nearest to the transmitted vector T
37 In case of real time vector discrete-time channel the input and output signals are not
vectors.
F
38 In a channel if ISI is present then we call it as discrete memoryless channel. F
39 While mapping the error will be maximum with the neighboring point rather than
distant point,
T
40 Gray coding cannot be assigned to 16-QAM F
41 In 16-QAM gray code the difference between vertical adjacent point is not one bit F
42 Gray encoder is the best mapper in communication. T
43 By using grey coding we can achieve the probability of bit errors same as probably of
symbol errors
T
44 For the same data rate to reduce the probability of error we should reduce the F
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distance between the points.
45 Upper bound of the probability of error is useful. T
46 Probability of error depends on how we reject the signal at the receiver. T
47 Matched filter is not an optimum receiver. F
48 In Matched filter output is maximum at t=T. T
49 The co variance of ni and nj T
50 For a Gaussian noise the probability of smaller noise is less compared to larger noise. F
51 Biorthogonal signals are symmetric signals. T
52 In case of modulation with memory the current transmitting signal will not depends
on previous transmitted signal also.
F
53 A differential encoded data represents modulation with memory. T
54 A differential PSK [DPSK] represents modulation with memory T
55 In DPSK, no synchronous carrier is needed at the receiver. T
56 In PSK, no synchronous carrier is needed at the receiver. F
57 In FSK, no synchronous carrier is needed at the receiver. F
58 Probability of error in DPSK is higher than PSK receiver. T
59 Among the basic modulation schemes (ASK, FSK and PSK), the probability of error in
PSK is minimum.
T
60 Probability of error in a non-coherent receiver is lower than the coherent receiver. F
61 FSK signaling scheme it is not compulsory to use orthogonal signals. T
62 Equalizers are used to reduce the effect of ISI. T
63 The disadvantage of peak distortion equalizer is it will amplify noise. T
64 The advantage of peak distortion equalizer is it will eliminate ISI completely T
65 In an optimum equalizer the mean square error is always maximum. F
66 A linear equalizer is not the best compensator for the severe ISI. T
67 Decision feedback equalizer is a nonlinear equalizer. T
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4.5) Frequently Asked Questions [FAQ]:
Questions Video
No
1 What is the advantage of using orthogonal signals in FSK modulation? 18
2 What is the difference between PPM and FSK schemes? 18
3 What is importance of inner product in the representation of modulation
schemes?
18
4 What is the advantage of bi-orthogonal scheme? 19
5 For bi-orthogonal scheme, which receiver (matched filter or correlation) is
better?
19
6 What are Simplex signals? 20
7 What is meant by memory less modulation technique? 20
8 What is modulation technique with memory? 20
9 What is an Eye diagram? 21
10 How noise margin is measured using Eye diagram? 21
11 What is the importance of a mapper? 21
12 What is the importance of Q-function? 22
13 What is the probability of error? 22
14 What is the difference between Probability of error and Bit error rate? 22
15 What is the importance of dimension of the signal set for the computation of
probability of error?
23
16 What is meant by union bound for signal set? 24
17 What is the difference between memory and memory less modulation
schemes?
24
18 What is an equalizer? What is its importance? 25
19 What is the principle of zero forcing equalizer? 25
20 What is the difference between peak distortion criterion and MSE criterion? 25
21 What is the difference between linear and adaptive equalizer? 25
22 What is meant by Spectral Efficiency?
23 Why Eb/No ratio is preferred for SNR in digital communication?
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1.6) Assignment Questions: Sl.
No.
Questions
1
2 Write the signal space diagram of FSK signal set for M=2 and M=3.
3 Show that the inner product of two signals:
xm n -n)].
4 Explain the PPM technique with waveforms for the different time shifting c
Compare them.
5 Derive the pulses for PPM scheme to transmit 8 symbols.
6 Explain the properties of orthogonal FSK and PPM modulation techniques. Compare them.
7 Compare the properties of Bi-orthogonal signals and orthogonal signals.
8 Show that both the correlation receiver and matched filter receivers for the demodulation of
bi-orthogonal signaling scheme produces the same output.
9 Derive an expression for probability of bit error of a coherent binary phase shift keying (PSK)
receiver.
10 Derive an expression for probability of bit error of a coherent binary frequency shift keying
(FSK) receiver considering orthogonal signals.
11
minimum error probability is . . Also determine the probability of error for this choice of
12 What are the properties of simplex signal set? Explain with suitable examples.
13 What is the advantage of using gray coding while mapping the signals? Explain how gray
coding is assigned with examples.
14 With block diagrams, explain the working of QPSK modulator and demodulator.
15 Illustrate the modulation and demodulation process in differential phase shift keying system
considering the binary data 1100101011.
16 Compare the spectral efficiency of the three digital modulation schemes-ASK,PSK and FSK.
17 Binary data having a bit rate of 10kbps is transmitted using binary PAM scheme. Find the
average bit energy and the signal amplitude required to achieve an error probability of 10-5
when the data is transmitted through an AWGN channel with noise power spectral density of
10-8 watts/Hz. Assume Q(4.27) = 10-5.
18 A digital communication system employing frequency shift keying scheme is used for
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transmitting information over an AWGN channel having power spectral density 10-9
Watts/Hz. The bit rate used is 2000 bits/sec. Determine the average bit energy and
probability of error when the signal amplitude at input of the receiver is A=10 milli-volts.
19 A coherent FSK system transmits binary data at the bit rate of 3Mbits/sec. In the absence of
the noise, the amplitude of the received signal is 1microvolt. During the transmission, white
Gaussian noise of zero mean and two sided power spectral density 10-20 watts/Hz is added to
the signal. Find the average probability of bit error.
20 A binary receiver system receives a bit rate of 1 Mbps. The waveform amplitude is 6 mV and
the noise power spectral density is 10-11 W/Hz. Calculate the average bit error probability if
the modulation schemes are (i) ASK,(ii)PSK, and (iii)FSK.
21 A binary DPSK system is to have an average probability of error, Pe < 10-4. If the average
transmitted power is 150 milliwatts, the channel attenuation is 80 dB and the additive zero-
mean white Gaussian noise on the channel is having a two-sided PSD of (10-15) W/Hz, find the
maximum allowable bit rate for transmission.
22 Explain the trade-off between bandwidth, average energy, bit rate and probability of error in
communication.
23 In order to transmit at 4.8 kbps over a channel with 3.2kHz bandwidth, which type of M-level
PSK would be most suitable BPSK, QPSK, or 8-PSK. Justify you answer.
24 Derive an expression for error probability of Quadrature Phase Shift Keying (QPSK) system.
Compare its spectral and power efficiency with that of BPSK system.
25 What is an equalizer? What are the functions performed by an equalizer?
26 Explain the role of the equalizer when the channel impulse response h(t) does not satisfy
Nyquist’s first criterion.
27 Compare the linear and adaptive equalizer.
28 Explain the working of decision feedback equalizer?
29 Explain the peak distortion equalizer? Is it same as the zero-forcing equalizer?
30 Determine the tap weight coefficients of a three-tap-zero forcing equalizer if the ISI spans
three symbols and is characterized by the values x(0)=1, x(-1)=0.3, x(1)=0.2. Also determine
the residual ISI at the output of the equalizer for the optimum tap coefficients.
Page 97 of 103
1.7) Test your skill:
Sl.
No.
Questions
1 Verify that the output of a correlator and a matched filter are maximum at t = T, even
though they may differ at other times.
2 Demodulation of binary antipodal signal can be accomplished by an integrate-and-dump
receiver followed by a detector. Determine the SNR at the output of the integrator
sampled at t = T.
3 In PPM method the information is present in the position of the pulse. Justify this
statement.
4 For the binary stream of data 1100100110 draw the waveforms for:
(i) Polar NRZ. (ii) Unipolar RZ code. (iii) Manchester code
5 Derive an expression for the power spectral density of NRZ polar format for the binary
data. Hence explain the bandwidth of the signal.
6 Compare the features orthogonal, bi-orthogonal and simplex signals.
7 A binary communication system employs the on-off signalling for transmission of the
information. The demodulator cross-correlates the received signal r(t) with s1(t) and
sampled the output of the correlator at t = T.
(i) Determine the optimum detector for an AWGN channel and the optimum threshold
assuming the signals are equally probable.
(ii) Find the probability of error as a function of the SNR.
8 The signals 1(t) = A. cos(2 ) and 2(t) = A. sin(2 ), for (0 < t T), where T is the
symbol duration, are used as basis functions for band pass digital modulation. Show that
1(t) and 2(t) are orthogonal over the interval (0 < t T). Assume = 2/ . 9 A binary PAM communication system is used to transmit data over an AWGN channel. The
Prior probabilities for the bits are P(1) = 1/3 and P(0) = 2/3. Find the average probability
of a bit error.
10 A binary signalling scheme uses the Manchester code to describe the symbols 1 and 0.
Assume that the receiver noise is white, Gaussian and zero mean and power spectral
density No/2. Determine the average probability of error when symbols 1 and 0 occur
with equal probability.
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11 A 1 Mbps BPSK receiver detects waveforms s1(t) 0t or s2(t)= - 0t with a
matched filter. (a) If A=1mV, what will be the average bit error probability? (b) What
should be the average received signal power to maintain an error probability of 2*10-3?
Assume single sided noise power spectral density to be N0=10-11W/Hz(c) Binary antipodal
signals are used in another scheme with amplitude of ±100V to transmit information over
an AWGN channel at a rate of 105bps. The psd N0/2=0.5*10-2w/Hz. Determine the error
probability achieved.
12 A simple binary communication system model, with additive Gaussian noise, is the
following: S is a binary random variable, representing the message bit sent, taking values
1 and +1 with equal probability. Additive noise is represented by a Gaussian random
variable Z of zero mean and variance 2. The received value is a random variable X = S + Z.
Find the probability density function (pdf) of X.
13 Binary PSK (BPSK) is used for data transmission over an AWGN channel with power
spectral density N0/2 = 10 10 W/Hz. The transmitted signal energy is Eb = A2T/2, where T is
the bit duration and A is the signal amplitude. Determine the value of A needed to achieve
an error probability of 10 6, if the data rate is: (i) 10000 bits/sec (ii) 100K bps.
14 A coherent FSK system transmits binary data at the bit rate of 2Mbits/sec. In the absence
of the noise, the amplitude of the received signal is 1microvolt. During the transmission,
white Gaussian noise of zero mean and two sided power spectral density 10-20 watts/Hz is
added to the signal. Find the average probability of bit error.
15 Determine the reduction in the transmission bandwidth and the average signal energy of
64 QAM and 16 QAM for the same probability of error to be obtained for both.
16 In a digital communication system, using coherent BPSK, it is necessary to keep the
degradation due to phase error to about 0.1 or less. How much of phase error can the
system tolerate?
17 Consider voice transmission using BPSK signaling at a transmission rate of 2400 bps and a
bandwidth efficiency of 1 bps/Hz. It is desired to increase the data rate to 9.6kbps. If the
number of points in the signal constellation is increased until the data rate becomes
9.6kbps while the symbol rate remains at 2400 symbols/sec determine the number of
constellation points.
18 Derive an expression for error probability of Quadrature Phase Shift Keying (QPSK) system.
Compare its spectral and power efficiency with that of BPSK system.
19 In a coherent BPSK system, the correlator in the receiver, to which the received PSK signal
Page 99 of 103
carrier phase. Determine the effect of this phase error
system.
20 The signal constellation diagram for an 8-QAM system is shown below.
(i) Suggest a suitable receiver structure.
(ii) Compute the probability of error for the receiver.
21 What is “Eye pattern”? Explain how it is useful in understanding the ISI problem?
22 Describe the role of the equalizer when the channel impulse response h(t) does not satisfy
Nyquist’s first criterion. Explain how the equalizer known as the linear transversal filter
fulfills this role and provide justification for the “tapped delay” structure of such an
equalizer.
23 Compute the tap weight coefficients of a three-tap-zero forcing equalizer if the ISI spans
three symbols and is characterized by the values x(0)=0.9, x(-1)=0.25, x(1)=0.25. Also
determine the residual ISI at the output of the equalizer for the optimum tap coefficients.
24 Mention the different types of memory less and memory modulation schemes.
25 Explain how storing data on a magnetic or optical disk is equivalent to transmitting a signal
over a radio channel.
26 What are the different types of multiple access schemes used in digital Communication?
Compare their characteristics.
Page 100 of 103
4.8) Additional Links: Module-4 General Links
http://www.youtube.com/watch?v=pZbczyghP8Y http://www.youtube.com/watch?v=2yXQ6VrbpKk http://www.youtube.com/watch?v=a-pjhbYkRFM http://demonstrations.wolfram.com/DigitalModulationQuadraturePhaseShiftKeyingQPSKSignalConstel/ http://freevideolectures.com/Course/2311/Digital-Communication
http://freevideolectures.com/Course/2177/Principles-of-Digital-Communication-II
http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-450-principles-of-digital-communications-i-fall-2006/lecture-notes/book_1.pdf
Q Nos
Question Videos Web Link
1 Digital Modulation http://www.youtube.com/watch?v=pZbczyghP8Y http://www.youtube.com/watch?v=2yXQ6VrbpKk
https://www.google.co.in/search?q=Digital+modulation&tbm=isch&tbo=u&source=univ&sa=X&ei=ASQvU-_oKIaNrQfnqYGgBA&ved=0CDIQsAQ&biw=1366&bih=596
http://web.ee.ccu.edu.tw/~wl/wenclass/95/IDCclass/Ch5_Digital.pdf
http://en.wikipedia.org/wiki/Shift_keying#Digital_modulation_methods
2 Shift keying techniques
www.youtube.com/watch?v=5o43sBgDYLA www.youtube.com/watch?v=Ez__KA00hD8 www.youtube.com/watch?v=Cf2hGhs2k-8 www.youtube.com/watch?v=c51oxnOGI5k www.youtube.com/watch?v=
www.ele.uri.edu/Courses/ele436/labs/ASKnFSK.pdf
https://www.fas.org/man/dod-101/navy/docs/es310/.../digicoms.html
http://en.wikipedia.org/wiki/Shift_keying#Digital_modulation_methods
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dE_nLy9abaY
www.youtube.com/watch?v=pNkTWgtUjDU
3 ASK, FSK, BPSK
http://www.youtube.com/watch?v=jTzqXywJVlc http://www.youtube.com/watch?v=oUcNdlKioDg http://www.youtube.com/watch?v=iT1GGT5R-9w
http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCcQFjAA&url=http%3A%2F%2Fwww.ni.com%2Fwhite-paper%2F7824%2Fen%2F&ei=dQwzU9_VHcmBrQevgYGYBg&usg=AFQjCNFtohrulplU8kmR0Q4XxoUBQ74q1Q&sig2=NzIO6ljp8NiPJv0eAob-ow&bvm=bv.63738703,d.bmk
http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0CDkQFjAC&url=http%3A%2F%2Fwww.slideshare.net%2Folamashaqi%2Fdiditalpres-final&ei=dQwzU9_VHcmBrQevgYGYBg&usg=AFQjCNFffZ-7sCA2m5qD736ZQEqgNT0o5A&sig2=KQw_wxGdZG6IWQJ-Kde9WQ&bvm=bv.63738703,d.bmk
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0CEIQFjAD&url=https%3A%2F%2Fwww.labvolt.com%2Fdownloads%2Fcwa8087_30.pdf&ei=dQwzU9_VHcmBrQevgYGYBg&usg=AFQjCNEsfULCQqZ0bnyOgfZMGVRA0n57ew&sig2=cFUHlQQXBovoCHNsYneYEg&bvm=bv.63738703,d.bmk
4 Probability of error www.youtube.com/watch?v=PQ48szd9cw0 www.youtube.com/watch?v=UWZZ5Ig3d8M www.youtube.com/watch?v=Dw3UR4-7qMA
www.ece.utah.edu/~npatwari/ece5520/lectureAll.pdf
www.ece.ualberta.ca/~chintha/resources/papers/2005/1431129.pdf
http://en.wikipedia.org/wiki/Bit_error_rate
5 Eye diagram www.youtube.com/watch?v=oBHytOmmiRU http://demonstrations.wolfram.com/DigitalModulationQuadraturePhase
www.engr.sjsu.edu/rmorelos/ee251f06/eyediagram_notes.pdf
http://en.wikipedia.org/wiki/Eye_diagram
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ShiftKeyingQPSKSignalConstel/
6 Equalizer http://www.youtube.com/watch?v=a-pjhbYkRFM
http://www.freewebs.com/angsuman/chapter5.pdf
http://en.wikipedia.org/wiki/Equalizer
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