Sample Paper of Digital Communication

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 B.Tech Sample Paper

Digital Communication

Time:3 hours                                                                                                      Maximum Marks:100

    Note: Attempt any five questions.Each question carry 20 marks.

Q 1. Explain the following terms with the help of suitable examples:

(i) Sampling Process

(ii) Aperture Effect

(iii) Noise in PCM

(iv) Delta sigma Modulation

Ans: (i) A continuous time signal may be completely represented in its samples and recovered back if the sampling frequency is less or equal to 2f.

(ii) The high frequency roll off acts like a low pass filter and thus attenuates the upper portion of the message signal spectrum.

(iii) The performance of it is influenced by channel noise and quantizing noise.

(iv) It means that when the signal is transmitted in delta modulation, the signal gets distorted with the noise.

Q 2. What do you mean by correlative level coding? Discuss the duo-binary signaling, its modified form and generalized form of correlative level coding.

Ans: If  inter symbol inference in a controlled manner is added to the transmitted signal, then it is possible to achieve a signaling rate equal to the Nyquist rate of 2W symbol per second.

Q 3. Explain BPSK. Calculate the error probability for BPSK.

Ans: BPSK stands for binary phase shift keying.the input binary sequence of 0 and 1 are converted into non return to zero bit. the modulated is obtained from the product modulator.

Q 4. What is quantization noise? Give difference between uniform and non-uniform type of quantization noise.

Ans: It is the process of transforming the sample amplitude of a message signal at a time into a discrete amplitude taken from a finite set of possible amplitude.

Q 5. (a) Explain the receiver of QPSK.                                                                      (10 Marks)

(b) Explain Delta Modulation.                                                                                      (10 Marks)

Ans: (a) In QPSK, the phase of the carrier takes on one of four equally spaced values. It has a two dimensional signal constellation.

(b) A delta modulation scheme the uses integration at its input is called delta sigma modulation. The message signal is defined in its continuous form.

Q 6. Discuss the following in brief:

(a) Code Division Multiplexing.                                                                                    (10 Marks)

(b) Time Division Multiplexing.                                                                                    (10 Marks)

Ans: (a) In code division multiplexing the  different codes are being given to each user to transmit the data.

(b) In time division multiplexing the user are given different time slots in which they will have to transmit their data.

Q 7. Briefly explain Tapped Delay Line Equalization and Adaptive Equalization.

Ans: In this the symbol rate of the tapped delay line is an image of multiple hop rate. This will have output wave to a mixer that consist of a multiplier followed by a band pass filter.

Q 8.(a)  What do you mean by Inter Symbol Interference?                                      (10 Marks)

       (b) Explain properties of matched filter with explanation energy to noise spectral density ratio (10 Marks)

Ans: (a) symbol inference means that the signals get mixed with the noise in the air and will cause problems.

(b) This has the following properties:

1.high speed

2.High quality

3.reliability

4.high performance

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