Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Summer 6th Sem 2161001 Digital Communication Previous Question Paper

Enrolment No.___________

**GUJARAT TECHNOLOGICAL UNIVERSITY**

**BE - SEMESTER? VI EXAMINATION ? SUMMER 2020**

**Subject Code: 2161001**

**Date:26/10/2020**

**Subject Name: DIGITAL COMMUNICATION**

**Time: 10:30 AM TO 01:00 PM**

**Total Marks: 70**

**Instructions:**

**1. Attempt all questions.**

**2. Make suitable assumptions wherever necessary.**

**3. Figures to the right indicate full marks.**

**MARKS**

**Q.1 (a)**What are the Nyquist criteria for the sampling of signal in communication?

**03**

Which kind of effect is observed if Nyquist criteria doesn't follow?

Explain with example.

**(b)**State the difference between PCM, DPCM and Delta modulation.

**04**

**(c)**Explain the T1 digital carrier System with frame structure, important

**07**

parameters and synchronization mechanism.

**Q.2 (a)**Modul

List ati

out on (D

the M)

im

portance characteristic of line codes and compare the On-

**03**

Off, Polar and Bipolar codes in terms of their Power Spectral Density

(PSD).

**(b)**Discuss the Trade-off between transmission rate and transmission power

**04**

for M-ary signal.

**(c)**State the importance of Regenerative repeater in digital communication

**07**

and discuss briefly about the significance of individual components of

Regenerative repeater.

**OR**

**(c)**What is the pulse shaping? Shed the light on Nyquist first and second

**07**

criteria for pulse shaping.

**Q.3 (a)**Establish the relationship between PDF and CDF and enlist the properties

**03**

of CDF.

**(b)**What is marginal probability? Explain with mathematical background

**04**

**(c)**Explain central limit theorem in a brief and draw the Probability

**07**

distribution function (PDF) and CDF for the Random Variable (R.V.).

obtain as a sum of large number of R.V.

**OR**

**Q.3 (a)**What is conditional probability? State the equation of conditional

**03**

probability for two variable case.

**(b)**A binary source generates digits 1 and 0 randomly with probabilities

**04**

*P*(1) = 0.8 and

*P*(0) = 0.2.

(a) What is the probability that two 1's and three 0's will occur in a five-

digit sequence?

(b) What is the probability that at least three 1's will occur in a five-digit

sequence?

**(c)**How many types of correlation does exists between two sets of R.V. ?

**07**

Explain with diagram and mathematical background.

**Q.4 (a)**Derive the equation for Shannon capacity and describe the tradeoff between

**03**

signal to noise ratio and bandwidth.

**(b)**What is entropy of message? In which case, Entropy will be maximum

**04**

explain with the mathematical background.

1

**(c)**A source emits seven messages with probability 1/2, 1/4, 1/8, 1/16, 1/32, 1/64

**07**

and 1/64 respectively. Find the entropy of the source. Obtain the compact binary

code and find the average length of the code word. Determine the efficiency and

redundancy of the code.

**OR**

**Q.4 (a)**State the difference between ASK, FSK and PSK in terms of their

**03**

important parameters.

**(b)**Explain the concept of GMSK with their transmitter and receiver block

**04**

diagram.

**(c)**What is QAM, ?. Draw Constellation diagram of 16- QAM. Discuss their

**07**

merits and demerits. Draw and explain the transmitter and receiver

structure of QAM.

**Q.5 (a)**Construct a (7,4) systematic cyclic code for data vector d= 10101 for the

**03**

Generator matrix g(x) = x3 + x2 +1.

**(b)**Derive the Hamming bound condition for error correcting codes.

**04**

**(c)**For a (6,3), Linear block code the parity check digits c4, c5 and c6 are as

**07**

follows:

c4= d1+d2+d3,c5= d1+d2, c6= d1 +d3. (+ sign is consider as X-OR Operation)

Draw the line block encoder, Generate the Matrix G and find the code

vector for following data vector : 001, 111, 010, 101. Comment on

maximum error correcting capacity of the code.

**OR**

**Q.5 (a)**What is the trade-off between code efficiency and reliability? Explain with

**03**

example.

**(b)**Explain Burst error detecting and correcting codes.

**04**

**(c)**What is convolution code? How it is differ than linear block code ? Draw

**07**

the encoder if out put V1 = S1 + S2 +S3 and V2 = S1 +S3, where S1, S2 and

S3 are the number of shift register, Entering data is fetching S1 first. What

is the output of convolution encoder if applied input is 10110. Draw the

state diagram for this encoder. (+ sign is consider as X-OR Operation)

.

.

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This post was last modified on 04 March 2021