**Anna University**

**Department of Computer Science Engineering**

**Third Semester**

**CS2204 - Analog and Digital Communication**

**Question Bank [2014-15] [MOST IMPORTANT]**

**UN****I****T 1 F****UNDA****MENTALS OF ****A****NAL****O****G ****C****O****MMUNICATION**

TEXT BOOK: Wayne Tomasi, “Electronic Communication Systems – Fundamental through advanced”, 5/e, Pearson Education. (for UNIT I to IV).

**P****A****RT – B**

1. Define modulation index for FM and PM and obtain the relation between modulation index

and modulating signal for FM and PM. (8)

2. Compare the advantages and disadvantages of angle modulation with amplitude modulation.(8)

3. Explain the principle of Amplitude Modulation and derive an expression for AM-DSBFC signal. Draw the AM waveform and frequency spectrum and explain the voltage distribution and power distribution in AM. (16)

4. Discuss about the sets of side frequencies produced when a carrier is Frequency Modulated by a single frequency sinusoid and Derive an expression for the average power of angle modulated wave. (16)

5. Explain any one method each for generating and receiving Amplitude Modulated and Angle

Modulated Signal. (16)

**P****ROBLEMS:**

1. To a conventional AM modulator, one input is a 500 KHz carrier with amplitude of 20 V

(peak). The other input is a 10KHz modulating signal that is of sufficient amplitude to cause a change in the output wave of ±7.5V (peak). Determine

(i) Upper and lower side frequencies.

(ii) Modulation coefficient and percent modulation.

(iii) Peak amplitude of the modulated carrier and the upper and lower side frequency voltages. (iv) Maximum and minimum amplitudes of the envelope.

(v) The expression for the modulated wave. (vi) Draw the output spectrum.

(vii) Sketch the output envelope. (16)

2. For an FM modulator with deviation sensitivity K1= 4 KHz/V and a modulating signal vm(t) = 10Sin(2π2000 t) , détermine,

(i) The peak frequency deviation

(ii) The carrier swing

(iii) and the modulation index.

(iv) What is the peak frequency deviation produced if the modulating signal were to double in amplitude. (8)

3. For an FM modulator with a modulation index m=1, a modulating signal

vm(t) = VmSin(2π1000 t) and an unmodulated carrier vc(t) = 10Sin(2π500Kt), determine,

(i) | The number of sets of significant side frequencies, | |

(ii) | Their amplitudes. | |

(iii) | Draw the frequency spectrum showing their relative amplitudes. | (6) |

6. The output of an AM transmitter is given by Vm(t) = 500(1 + 0.4 sin3140t)sin(6.28x107t).

Calculate the (1) Carrier frequency

(2) Modulating frequency

(3) Modulation index

(4) Carrier power if load is 600 Ω.

(5) Total power.

**UN****I****T 2 – D****IGITAL ****C****O****M****MUNICATION**

1. With neat block diagrams, explain Binary FSK modulator and demodulator system and discuss the bandwidth requirements. (16)

2. Explain the generation and detection of BPSK system with the help of block diagrams. Also obtain the minimum double sided Nyquist bandwidth. (16)

3. Discuss in detail the operation of QPSK modulator and demodulator with its truth table, phase diagram and constellation diagram.(16)

4. Define QAM. Illustrate the concept of 8-QAM transmitter with the truth table and explain the 8- QAM receiver. (8)

5. What is carrier recovery? Discuss how carrier recovery is achieved by Squaring loop and Costas loop circuits in detail.(16)

**P****ROBLEMS:**

1. For a BPSK modulator with a carrier frequency of 70 MHz and an input bit rate of 10 Mbps,

determine

(i) Maximum and minimum upper and lower side frequencies

(ii) Sketch the output spectrum

(iii)Minimum Nyquist bandwidth and baud rate. (16)

2. For a QPSK modulator with an input data rate equal to 12 Mbps and a carrier frequency of 100

MHz, determine the following

(i) Minimum double sided Nyquist bandwidth

(ii) Baud rate

(iii)Sketch the output spectrum (8)

3. For the DPSK modulator determine the output phase sequence for the following input bit sequence: 11001100101010. Assume that the reference bit is equal to 1. (8)

4. Determine the bandwidth and baud for an FSK signal with a mark frequency of 32KHz, a space frequency of 24KHz and a bit rate of 4Kbps. (4)

5. Define bandwidth efficiency. For an 8-PSK system, operating with information bit rate of 24 kbps, determine (i) Baud (ii) Minimum bandwidth (iii) Bandwidth efficiency. (4)

6. For a QPSK modulator with an input data rate equal to 10 Mbps and a carrier frequency of 75

MHz, determine the minimum double sided Nyquist bandwidth.(4)

7. Determine the (1) peak frequency deviation and (2) minimum bandwidth, for a binary FSK

signal with mark frequency of 45 KHz and an input bit rate of 3 Kbps. (4)

**UN****I****T 3 – D****IGITAL ****T****RAN****SMISSION**

1. With neat block diagram explain Pulse Code Modulation (PCM) system and explain the

advantages and disadvantages of digital transmission. (16)

2. Draw and explain the Sample and Hold circuit and Compare natural sampling and flat top sampling. (16).

3. Explain Delta modulation PCM Transmitter and Receiver. Describe slope overload distortion and granular noise. What are the ways to reduce this noise? (16)

4. Explain Differential Pulse Code Modulation (DPCM) system with block diagram. (16)

5. What is ISI? What are the causes of ISI? (8)

**P****ROBLEMS:**

1. A 12 bit linear PCM code is digitally compressed into 8 bits. The resolution is 0.03V.

Determine the following for an analog input voltage of 1.465V. (8) (i) 12 bit linear PCM code.

(ii) Eight bit compressed code. (iii) Decoded 12 bit code.

(iv) Decoded voltage

(v) Percentage error.

2. For minimum line speed with an 8 bit PCM for speech signal ranging upto 1 volt, (i) Calculate the resolution and quantization error.

(ii) Calculate the coding efficiency for a resolution of 0.01 volt with the 8 bit PCM. (4)

3. For a compressor with µ = 255, determine

(i) The voltage gain for the following relative values of Vin, Vmax, 0.75Vmax, 0.5Vmax,

0.25Vmax.

(ii) The compressed output voltage for a maximum input voltage of 4 V.

(iii) Input and output dynamic ranges.

(iv) Compression. (10)

ALL THE SOLVED PROBLEMS IN THE TEXT BOOK – Wayne Tomasi. CHAPTER-10

**UN****I****T 4 – D****AT****A ****C****O****M****MUNICATIONS**

[Wayne Tomasi. CHAPTER- 21, 22]

1. Write about the various Error Detection techniques and Error Correction techniques. (16)

2. Describe the physical, electrical and functional characteristics of RS 232 interface (16)

3. Explain data communication modem with a block diagram and write short notes on

Asynchronous modems and Synchronous modems. (16)

4. Write short notes about the history of data communications and about the standards and organizations for data communication. (16)

**UN****I****T 5 – S****P****REA****D ****S****PECTRUM AND ****M****ULT****I****P****L****E ****A****CCE****SS ****T****EC****H****N****I****Q****UE****S**

TEXT BOOK: Simon Haykin, “Communication Systems”, 4th Edition, John Wiley & Sons., 2001.

1. Define Pseudo noise sequence? How PN sequence is generated using LFSR? Explain with an example. Write about the properties of the PN sequence. (16)

2. Describe direct sequence spread spectrum (DS-SS) with coherent BPSK. (16)

3. Describe Slow and Fast Frequency Hopping spread spectrum (FH-SS). (16)

4. With typical examples for each explain TDMA and CDMA. [(ie) Explain GSM and IS -95 wireless communication systems] and Compare the merits and demerits of TDMA and FDMA multiple access schemes. (16)

5. Explain the working of Multi pulse excited Predictive Coding and Code excited Predictive coding with suitable diagrams. (16)