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Code No: 07A5EC09 Set No. 4<br />
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD<br />
III B.Tech. I Sem., II Mid-Term Examinations, November – 2010<br />
DIGITAL COMMUNICATIONS<br />
Objective Exam<br />
Name: ______________________________ Hall Ticket No.<br />
Answer All Questions. All Questions Carry Equal Marks.Time: 20 Min. Marks: 20.<br />
I Choose the correct alternative:<br />
1) For the data word 1110 in a (7, 4) non-systematic cyclic code with the generator<br />
polynomial 1+x+x 3 , the code polynomial is [ ]<br />
a) 1+x+x 3 +x 5 b) 1+x 2 +x 3 +x 5 c) 1+x 2 +x 3 +x 4 d) 1+x 4 +x 5<br />
2) A source X with entropy 2 bits/message is connected to the receiver Y through a noise free<br />
channel. The conditional probability of the source is H(X/Y) and the joint entropy of<br />
the source and the receiver H(X, Y). Then [ ]<br />
a) H(X,Y)= 2 bits/message b) H(X/Y)= 2 bits/message<br />
c) H(X, Y)= 0 bits/message d) H(X/Y)= 1 bit/message<br />
3) Which of the following is a p(Y/X) matrix for a binary Erasure channel [ ]<br />
a) 11ppqq−⎡⎤⎢⎥−⎣⎦ b) c) d) None<br />
4) The channel matrix of a noiseless channel [ ]<br />
a)consists of a single nonzero number in each column.<br />
b) consists of a single nonzero number in each row.<br />
c) is an Identity Matrix. d) is a square matrix.<br />
5) Information content of a message [ ]<br />
a) increase with its certainty of occurrence. b) independent of the certainty of<br />
occurrence.<br />
c) increases with its uncertainty of occurrence. d) is the logarithm of its uncertainty of<br />
occurrence.<br />
6) The channel capacity of a BSC with the transition probability ½ is [ ]<br />
a) 0 bits b) 1 bit c) 2 bits d) infinity<br />
7) For the data word 1110 in a (7, 4) non-systematic cyclic code with the generator<br />
polynomial 1+x 2 +x 3 , the code polynomial is [ ]<br />
a) 1+x+x 3 +x 5 b) 1+x 2 +x 3 +x 5 c) 1+x 2 +x 3 +x 4 d) 1+x+x 5<br />
8) A source transmitting ‘m’ number of messages is connected to a noise free channel. The<br />
capacity of the channel is [ ]<br />
a) m bits/symbol b) m 2 bits/symbol c) logm bits/symbol d) 2m bits/symbol<br />
9) Which of the following is a p(Y/X) matrix for a binary symmetric channel [ ]<br />
a) b) c) d) None<br />
Cont…..2