Exam Details
Subject | digital communications | |
Paper | ||
Exam / Course | b.tech | |
Department | ||
Organization | Institute Of Aeronautical Engineering | |
Position | ||
Exam Date | January, 2019 | |
City, State | telangana, hyderabad |
Question Paper
Hall Ticket No Question Paper Code: AEC009
INSTITUTE OF AERONAUTICAL ENGINEERING
(Autonomous)
Four Year B.Tech V Semester End Examinations (Supplementary) January, 2019
Regulation: IARE R16
DIGITAL COMMUNICATIONS
Time: 3 Hours Max Marks: 70
Answer ONE Question from each Unit
All Questions Carry Equal Marks
All parts of the question must be answered in one place only
UNIT I
1. State and prove sampling theorem and explain various types of sampling techniques.
Determine the processing gain of a DPCM system with a first order predictor, if the message
signal has a normalized auto-correlation function of 0.8 for a lag of one period, assuming that
the predictor is designed to minimize the mean square value of the prediction error.
2. Explain PCM modulation and demodulation system with neat sketches. Describe the quantization
noise in PCM.
Find the maximum amplitude of a 1 KHz sinusoidal signal input to a delta modulator that will
prevent slope overload, when the sampling rate is 10,000 samples/sec and the step size is
0.1
UNIT II
3. Explain binary PSK and QPSK with corresponding equations and constellation diagrams.
For the signals, the given bit rate is 10Kbps. Estimate the bandwidth for Amplitude Shift Keying
and Frequency Shift Keying signals.
4. Explain the Non-coherent detection of FSK modulation scheme.
The bit stream 11011100101 is to be transmitted using DPSK. Determine the encoded sequence
and the transmitted phase sequence.
UNIT III
5. Describe the scrambling coding scheme HDB3 and Sketch the signal corresponding to the bit
sequence "01100000000100001100" using rectangular pulses.
Define roll off factor and describe the Nyquist bandwidth requirement of raised cosine filter for
distortion less transmission.
6. What is pulse shaping? Why it is useful in baseband transmission? Explain in detail.
Draw and explain the block diagram of modified duo-binary signaling scheme consider the binary
sequence bk= "01001101" applied to the input of a precoded modified duo-binary sequence.
Determine the sequence ak at the pre-coder output.
Page 1 of 2
UNIT IV
7. Calculate the Conditional entropy, mutual information and channel capacity using channel matrix
for a noise free channel.
Illustrate the principle of Frequency hopped spread spectrum. What is the minimum number
of bits in a PN sequence if we use FHSS with a channel bandwidth of B KHz and Bss=100
KHz?
8. Describe Code Division Multiple Access(CDMA) in detail.
Apply Shannon fano coding for the 5 messages with probabilities 0.4, 0.15, 0.15, 0.15, 0.15 and
find the coding efficiency.
UNIT V
9. Define the following terms
Code word
Block length
Code rate
Channel data rate
Code vector
Hamming distance
Minimum distance
Determine the generator polynomial for A cyclic code and find the code vector for
the following data vector 1010, 1111 and 1000.
10. Explain how generator and parity matrices are obtained for cyclic codes with an example.
Decode the given sequence 11 01 01 10 01 of a convolutional code with a code rate of and
constraint length using viterbi decoding algorithm.
Page 2 of 2
INSTITUTE OF AERONAUTICAL ENGINEERING
(Autonomous)
Four Year B.Tech V Semester End Examinations (Supplementary) January, 2019
Regulation: IARE R16
DIGITAL COMMUNICATIONS
Time: 3 Hours Max Marks: 70
Answer ONE Question from each Unit
All Questions Carry Equal Marks
All parts of the question must be answered in one place only
UNIT I
1. State and prove sampling theorem and explain various types of sampling techniques.
Determine the processing gain of a DPCM system with a first order predictor, if the message
signal has a normalized auto-correlation function of 0.8 for a lag of one period, assuming that
the predictor is designed to minimize the mean square value of the prediction error.
2. Explain PCM modulation and demodulation system with neat sketches. Describe the quantization
noise in PCM.
Find the maximum amplitude of a 1 KHz sinusoidal signal input to a delta modulator that will
prevent slope overload, when the sampling rate is 10,000 samples/sec and the step size is
0.1
UNIT II
3. Explain binary PSK and QPSK with corresponding equations and constellation diagrams.
For the signals, the given bit rate is 10Kbps. Estimate the bandwidth for Amplitude Shift Keying
and Frequency Shift Keying signals.
4. Explain the Non-coherent detection of FSK modulation scheme.
The bit stream 11011100101 is to be transmitted using DPSK. Determine the encoded sequence
and the transmitted phase sequence.
UNIT III
5. Describe the scrambling coding scheme HDB3 and Sketch the signal corresponding to the bit
sequence "01100000000100001100" using rectangular pulses.
Define roll off factor and describe the Nyquist bandwidth requirement of raised cosine filter for
distortion less transmission.
6. What is pulse shaping? Why it is useful in baseband transmission? Explain in detail.
Draw and explain the block diagram of modified duo-binary signaling scheme consider the binary
sequence bk= "01001101" applied to the input of a precoded modified duo-binary sequence.
Determine the sequence ak at the pre-coder output.
Page 1 of 2
UNIT IV
7. Calculate the Conditional entropy, mutual information and channel capacity using channel matrix
for a noise free channel.
Illustrate the principle of Frequency hopped spread spectrum. What is the minimum number
of bits in a PN sequence if we use FHSS with a channel bandwidth of B KHz and Bss=100
KHz?
8. Describe Code Division Multiple Access(CDMA) in detail.
Apply Shannon fano coding for the 5 messages with probabilities 0.4, 0.15, 0.15, 0.15, 0.15 and
find the coding efficiency.
UNIT V
9. Define the following terms
Code word
Block length
Code rate
Channel data rate
Code vector
Hamming distance
Minimum distance
Determine the generator polynomial for A cyclic code and find the code vector for
the following data vector 1010, 1111 and 1000.
10. Explain how generator and parity matrices are obtained for cyclic codes with an example.
Decode the given sequence 11 01 01 10 01 of a convolutional code with a code rate of and
constraint length using viterbi decoding algorithm.
Page 2 of 2
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