Modern Digital Communication Techniques Question Paper 2014 for BPUT M.Tech In Electronics and Telecommunication branch is given below. This question paper was asked in the BPUT M. Tech 1st semester Exam of Electronics and Telecommunication Engineering Branch . This question paper was common for the below given branch also (Communication Engineering, Communication System, Electronics & Communication Engineering, Electronics & Tele Communication Engineering). Prepare this previous year M.Tech question to score good marks.

**Modern Digital Communication Techniques Question Paper 2014**

**1st Semester Regular/ Back Papers 2014**

**Branch : Communication Engineering, Communication System, Electronics & Communication Engineering, Electronics & Tele Communication Engineering**

**Time : 3 Hours**

**Max. Marks : 70 Marks**

**Q1. Answer the following questions:**

a) Write the probability Mass Function (PMF) for the Bernoulli Random Variable.

b) Write any two properties of gamma function.

c) Write the equation for the mean and the variance of Nakagami Random variable.

d) Write any two difference between multi channel and multi carrier system.

e) Sate the central limit theorem.

f) Define white process and write any two properties of this process..

g) Define binary antipodal signaling.

h) Draw the signal space diagrams for BPSK, QPSK and 8 PSK?

i) Why FSK signaling belongs to the class of nonlinear modulation schemes?

j) Write the need for symbol synchronization in digital communication.

**Q2.**

a) The PDF of a random variable X is p(x). A random variable Y is defined as Y = aX=b where a <0. Determine the PDF of Y interm of the PDF of X.

b) Assume that random process X (t) and Y(t) are individually and jointly stationary.

i. Determine the autocorrelation function of Z(t) = X(t) + Y(t)

ii. Determine the autocorrelation function of Z(t) when X(t) and Y(t) are uncorrelated.

iii. Determine the autocorrelation function of Z(t) when X(t) and Y(t) are uncorrelated and havce zero means.

**Q3.** What is Orthogonal Frequency Division Multiplexing (OFDM). Describe the modulation and demodulation techniques of OFDM system.

**Q4.**

a) Explain the power spectral density for linearly modulated signals.

b) A speech signal is sampled as a rate of 8 kHz, and then encoded using 8 bits per sample. The resulting binary data are then transmitted through an A WGN baseband channel via M-level PAM. Determine the bandwidth required for transmission when M=4 and M=8.

**Q5.**

a) Calculate the error probability for PSK signaling.

b) Determine the ML phase estimate for offset QPSK.

**Q6.**

a) Calculate the capacity of a non ideal filter channel.

b) Explain briefly about Direct Sequence Spread Spectrum (DSSS) signals.

**Q7.**

a) Explain carrier recovery and symbol synchronization for Mary PSK signal demodulation with proper block diagram.

b) Explain 4 QAPSK with constellation diagram. Differentiate QAPSK and PSK.

**Q8. Write short notes (Any Two)**

a) The Ricean Random Variable

b) The Karhunen-Loeve Expansion

c) Binary PSK receiver

d) Phase-Locked Loop