Download AKTU B-Tech 6th Sem 2016-2017 NEC602 Digital Communication Question Paper

Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 6th Semester (Sixth Semester) 2016-2017 NEC602 Digital Communication Question Paper

PrintedPages :2 Roll No.| l l l l I l l l l l NEC602
B. TECH.
THEORY EXAMINATION (SEM?VI) 2016-17
DIGITAL COMMUNICATION
Time : 3 Hours Max. Marks : 100
Note : Be precise in your answer. In case Ofnumerical problem assume data wherever not provided.
SECTION ? A
1. Attempt all parts of the following questions: 10 x 2 = 20
(a) In an experiment a trial consists of four successive with draw of playing cards from a
pack of 52 cards. If we define RV X as number of king appearing in a trial. Find Fx(x)
(b) Calculate the autocorrelation for White noise.
(c) What is the condition to justify the orthogonality of two signals?
((1) What is essential bandwidth for polar N RZ line codes?
(e) Explain the difference between slow hopping and fast hopping.
(1') Compare the spectrum occupancy of PSK and FSK schemes.
(g) Explain the Bay?s rule of probability.
(h) Explain the advantages of Manchester coding.
(i) Draw the Manchester representation for the sequence 1010101001111
(j) Discuss BPSK modulator.
SECTION ? B
2. Attempt any five parts of the following questions: 5 x 10 = 50
(3) Find the PSD Sy(f) for a polar random signal use a basic pulse as shown in fig. below.
The digits are 1 and 0 equally likely and digits are transmitted every Tb seconds. Each
digit is in dependent of the remaining digits.
1
?Tb/ 4 0 Tb/4 1 |:?>
(b) Explain the working of frequency hopping spread spectrum system. Discuss its
applications in detail. A slow FH/MFSK system has following parameters:
(i) The number of bits per MFSK symbol = 4
(ii) The number of MFSK symbols per hop = 5
(iii) Calculate the processing gain of the system in decibels.
(c) What is the probability of error in presence of white noise for BPSK system? We are
required to transmit 2.08 x 106 binary digits per second with Pb S 10?7. The channel
noise PSD is Sn(f) = 10?8. Determine the transmission bandwidth and signal power
required in binary.
(d) A binary communication channel, the receiver detects the pulse with an error
probability Pe. What is the probability that out Of 100 received digits, no more than
four digits are in error.
(e) A source emits one of the four messages randomly every microsecond. The
probabilities of these messages are 0.4, 0.3, 0.2 and 0.2. Messages are generated
independently.

(i) What is the source entropy?
(ii) Obtain a compact binary code determine the average length, efficiency and
redundancy of codeword.
(f) Explain the convolution codes, their advantage and disadvantage.
(g) Explain the Chebyshev?s Inequality.
(h) What is a PN sequence? Draw the PN sequence generator and define its autocorrelation
function. A PN Sequence is generated using linear feedback shift register with number
of stages equal to 10. The chip rate is 107 per second. Find the following:
(i) PN sequence length (ii) chip Duration (iii) period Of PN sequence
SECTION ? C
Attempt any two parts of the following questions: 2 x 15 = 30
3. Explain the principle of OFDM.
4. (i) Write a short note on Matched Filter.
(ii) Find the probability of error for a matched filter? Explain how a matched filter
works as correlator receiver.
5. Write short notes on :
(i) Central limit theorem (ii) Error Correcting codes