 MORE IN Digital Communication
SPPU Electronics and Telecom Engineering (Semester 5)
Digital Communication
December 2015
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

Solve any one question from Q1 and Q2
1 (a) Explain with the help of block diagram formatting and transmission of baseband signal.
8 M
1 (b) Define mean, correlation, standard deviation of a random process.
6 M
1 (c) Draw the block diagram of DM transmitter and explain its working. Comment on the drawbacks of DM.
6 M

2 (a) Define the terms related to digital communication
i) Messages
ii) Characters
iii) Symbols
6 M
2 (b) Explain digital signal hierarchy using TI carrier system.
6 M
2 (c) The output of an oscillator is described by x(t)=A cos(π Ft+θ) where the amplitude A is constant and F and φ are independent random variables. The probability density function of θ is defined by [ f_\phi( heta) = \left{egin{matrix} \frac {1}{2 \pi}, & 0 \le \theta \le 2\pi \0 & \text{otherwise} \end{matrix} ight. ] Find the power spectral density of x(t) in terms of the probability density function of the frequency F.
8 M

Solve any one question from Q3 and Q4
3 (a) Consider the signal S(t) shown in fig. Determine the impulse response of a filter matched to this signal and sketch it as a function of time, plot the matched filter output as a function of time. 8 M
3 (b) Derive the expression of SNR for optimum filter.
8 M

Write a short note on:
4 (a) (i) MAP
4 M
4 (a) (ii) LRT
4 M
Draw & explain signal space representation of following signal.
4 (b) (i) BPSK
4 M
4 (b) (ii) 8 Array PSK
4 M

Solve any one question from Q5 and Q6
5 (a) Explain block diagrams for generation and reception of M-ary PSK signals. With suitable mathematical expressions, signal space representation Bandwidth and PSD.
10 M
5 (b) Binary data is transmitted using PSK at a rate 3M bps over RF link having bandwidth 10MHz. Find signal power required at receiver input so that error probability is less than or equal to 10-4 Assume noise PSD to be 10-10 watt/Hz. [Q (3.71) = 10-4 ]
8 M

6 (a) Explain with block diagram QPSK receives Write an expression for its error probability
8 M
6 (b) find error probability of coherent FSK when amplitude of I/P at coherent optimal receiver is 10mv and frequency 1MHz, the signal corrupted with white noise of PSD 10-9 W/Hz. the data rate is 100kbps. [erfc (1.01) = 0.1531, erfc (1.11) = 0.1164, erfc (1.22) = 0.0844 & erfc (1.33 = 0.0599)].
10 M

Solve any one question from Q7 and Q8
7 (a) Draw and explain 4bit P.N. sequence generator and find maximum length sequence.
8 M
7 (b) The signal has the following parameter number of bits per MFSK symbol K = 2 number of MFSK tone M = 2k = 4 length of PN sequence per hop K = 3 total No. frequency hops 2k = 8 sketch the o/p transmits freq of fast FH/MFSK signals.
8 M

8 (a) Write a short note on personal communication system (PCS).
8 M
8 (b) Compare DSSS with FHSS system.
8 M

More question papers from Digital Communication