Anna University Chennai 2005 B.Tech Electronics and Communications Engineering B.E./:DIGITAL COMMUNICATION - Question Paper

B.E./B.TECH.DEGREE EXAMINATION, NOV / DEC 2005
VI -SEMESTER
DIGITAL COMMUNICATION


TIME : three HRS
MAX MARKS : 100


PART - A (10 X two = 20 MARKS)

1. What do you understand by the term aliasing?

2. A bandpass signal has the spectral range that extends from 20 KHz to 82 KHz. obtain the acceptable range of sampling frequency .

3. What is the purpose of using eye pattern?

4. Why do you need adaptive equalization in a switched telephone network ?

5. Draw an illustrative figure to show the operation of a correlation receiver.

6. Highlight the major difference ranging from a QPSK signal and a MSK signal.

7. discuss the fundamental difference ranging from block codes and convolational codes.

8. How will you describe coding gain with reference to fault control codes?

9. Write down the properies of PN sequences.

10. How do you describe processing gain for a DS-CDMA system?

PART - B (5 X16 =80 MARKS)

11. (i) Derive expression for the quantization noise and signal-to -noise in a PCM system using a uniform quantizer

(ii) A sinusoidal signal is transmitted using PCM. An output SNR of 55.8 dB is needed .Find the number of representation levels needed to achieve this performance.

12 (a) What do you understand by the term inter symbol onterference (ISI) ? explain in detail the Nyquist criterian for minimizing ISI. discuss the difficulties in implementing it in a practical system.
(OR)

(b) (i) explain the merits and demerits of Duobimanary signalling.

(ii) The binary data (011100101) are applied to the input of Duobinary encoder.Construct the Duobinary output and the corresponding receiver output,without a precoder.Suppose due to fault in transmission,the level produced by the 3rd digit is decreased to zero, construct the new receiver output.

13 (a) discuss he BPSK signal transmission and coherent BPSK reception with suitable diagrams.Derive an expression for the probability of symbol fault for the scheme.
(OR)

(b) discuss the basis of operation in a matched fiter receiver with suitable diagrams. Derive the condition for which the output signal -to -noise ratio is maximized

14 (a) A (15 , five ) linear cyclic code has a generator polynomial, g (D) = one + D + D ^2 + D^4 + D^5 + D^8 +D ^10.
Draw the block diagram of an encoder and syndrome calculatorfor this code. obtain the code plynomial in systematic form , for the message polynomial m(D) = one + D^4 + D ^6 + D^8+ D^14, a code polynomial? If not , obtain the syndrome of y(D).

OR

(b) Consider a rate -1/2, a non-sstematic convolutional code with g ^ (1) ={1,0,1} and g ^ (2) = {1,1,1,}.Determine the encoder output corresponding to the data sequence {1 0 one 1 01 }.If the 1st and the 4th bits of the encoded sequence are affected during transmission, demonstrate the fault correcting capability of viterbi algorithm.

15 (a) Derive the probablity fault for a direct sequence spread BPSK system, affected only by an interfering signal , using the signal space approach. Also find the jamming margin. What does it imply?
OR

(b) explain a suitable method for generating PN sequences. discuss with suitale diagrams how the PN sequences is used in a frequency hoppng spread spectrum transmitter and receiver

Earning:   Approval pending.