THENI KAMMAVAR SANGAM COLLEGE OF TECHNOLOGY

KODUVILARPATTI, THENI – 625 534

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
INTERNAL ASSESSMENT II
Branch/Year/Sem : CSE/II/III Date :18.09.2019
Subject Code/Name : EC8395/ Communication Engineering
Time : 1.30 Hrs Max. Marks : 50
Answer All Questions
PART – A (10×2=20) BT CO
Level
1. Given the input binary sequence 1100100010, sketch the waveforms of the in-phase and quadrature 3 2
components of a modulated wave obtained by using QPSK.

2. Write the difference between BPSK and DPSK. 4 3

BPSK
Directly phase modulates the Indirectly phase modulates the
carrier carrier
Coherent method needs carrier Non- Coherent method not
at receiver required carrier at receiver
BW=2fb BW=fb
Error is less Error is high than BPSK
:

3. What is binary phase shift keying? 1 2

Binary Phase Shift Keying (BPSK) is a two phase modulation scheme, where the 0's and 1's in
a binary message are represented by two different phase states in the carrier signal: for binary 1 and
for binary 0.It can be noted that the carrier phases are apart and it has constant envelope.
4. What is ISI? And write the condition for zero ISI. 1 2
Inter symbol interference (ISI) occurs when a pulse spreads out in such a way that it interferes with
adjacent at the sample instant.
P(i-k)Tb = { 1 for i=k
0 for i≠k
5. What is ideal nyquist channel? 1 2
The ideal nyquist channel uses sinc pulse for transmission
P(t) = sin(2πB0t)/ 2πB0; P(t) = { ½ B0 -B0<f< B0
0 elsewhere
6. Draw 8-QAM Modulator phasor diagram. 4 3

7. List the effects of M in M’ary digital modulation techniques 1 2

In M-ary modulation, we can preserve bandwidth if we keep the symbol rate the same and increase the
number of bits per symbol.
8. What are eye patterns? 1 2
In telecommunication, an eye pattern, also known as an eye diagram, is an oscilloscope display in which
a digital signal from a receiver is repetitively sampled and applied to the vertical input, while the data rate
 is used to trigger the horizontal sweep. It is so called because, for several types of coding, the pattern
looks like a series of eyes between a pair of rails. It is a tool for the evaluation of the combined effects of
channel noise and inter symbol interference on the performance of a baseband pulse-transmission system.
9. Why do we need equalization in base band pulse transmission? 4 2
Equalization or equalization is the process of adjusting the balance between frequency components
within an electronic signal. The most well known use of equalization is in sound recording and
reproduction but there are many other applications in electronics and telecommunications. The circuit or
equipment used to achieve equalization is called an equalizer. These devices strengthen or weaken the
energy of specific frequency bands or "frequency ranges".
10. Define PSK and draw the PSK waveform for the data 101010. 1 2
Phase-shift keying (PSK) is another form of angle-modulated, constant-amplitude digital modulation.

PART – B (2X10= 30)

11. (a) Draw the block diagram of 8-QAM transmitter and explain its working. (10) 2 2

Explanation for each block

(OR)
(b) Explain adaptive equalization for data transmission. (10) 2 2

Explanation for each block

12. (a) Explain about DPSK and write how it eliminates the drawback of BPSK? (10) 2 3
DPSK Transmitter

Explanation for each block

(OR)
(b) Explain the generation and detection of QPSK in detail. (10) 2 2
 QPSK Detection:

Explanation for each block

PART – C (1×10= 10)
13. (a) Explain how eye pattern is used to study the performance of a data transmission system. (10) 4 2
(OR)
(b) Write short notes on Duo-binary encoding and cosine filters. (10) 2 3
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BT Level: 1- Remembering, 2- Understanding, 3- Applying, 4- Analyzing

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