AGNI COLLEGE OF TECHNOLOGYTHALAMBUR, CHENNAI.INTERNAL EXAM II- set 1

SUB NAME: DIGITAL COMMUNICATION TIME: 8.40 -10.10 am SUB CODE:EC2301 DEPT: ECE YEAR/SEC: III ECE ADATE: 10.9.14 Part A (Answer all questions) 1. Define quantization noise power.2. Define Hamming distance and calculate its value for two code words 11100 and 11011.3. State any 2 desirable qualities of line codes.4. Differentiate principles of temporal and model based encoding.5. What is Quadrature mirror filter?Part B6.(a) Describe DPCM technique with a neat block diagram. Also derive the slope overload factor for DPCM. How is the SNR improved in DPCM over the PCM? (8+4+4)Or(b) (i) What is Delta Modulation? (2) (ii) Draw the block diagram of DM transmitter and receiver. (6) (iii) Derive the predicted value mq(k) of the input signal m(k). (4) (iv) Draw the graph for the Delta modulated signal. (4)

7. (a) (i) Explain Pulse code modulation with neat block diagram. (8) (ii) Derive the expression for calculation of word size of PCM. (4) (iii) Also explain the bandwidth of a PCM signal.(4)Or(b) Explain Linear Predictive coding with neat diagram. Also derive the equations for finding the filter coefficients and Gain G. (16)8. (a) Determine the generator polynomial g(x) for a (7,4) cyclic code and find code vectors for the following data vectors 1010, 1111 and 1000. (8)Or (b) Explain Sub Band coding of speech signals. State its advantages. (8)

AGNI COLLEGE OF TECHNOLOGYTHALAMBUR, CHENNAI.INTERNAL EXAM II- set 2

SUB NAME: DIGITAL COMMUNICATION TIME: 8.40 -10.10 am SUB CODE:EC2301 DEPT: ECE YEAR/SEC: III ECE ADATE: 10.9.14 Part A (Answer all questions)1. Mention the properties of cyclic code.2. Define minimum distance and minimum weight of linear block codes.3. Define a systematic linear block code.4. What is the advantage of convolutional codes over linear block codes?5. What is meant by code rate? Calculate the code rate of a (6,3) block code for linear block codes.

Part B

6. (a) (i) Compare the various speech encoding methods in terms of transmission rate and number of coder bits.(8) (ii) Construct a single error correcting (7,4) linear block code and the corresponding decoding table.(8)Or(b) Derive the expression for the PSD of unipolar NRZ line code and discuss its characteristics.(16)

7. (a) Explain how encoding is done by convolutional codes with a suitable example. Draw its tree diagram, trellis diagram. (16)Or (b) Explain Linear Predictive coding with neat diagram. Also derive the equations for finding the filter coefficients and Gain G.(16)

8. (a) Briefly describe the concept of error free communication. (8)

Or

(b) Explain Sub Band coding of speech signals. State its advantages. (8)

Name of the staff: S.ChandravadhanaSignature of the staff:Signature of the HOD:Number of copies: 65

7. Mention the properties of cyclic code.8. Define minimum distance and minimum weight of linear block codes.9. Define a systematic linear block code.10. What is the advantage of convolutional codes over linear block codes?11. What is meant by code rate? Calculate the code rate of a (6,3) block code for linear block codes.