DATA COMMUNICATIONS (Electronics and Computer Engineering) Time: 3 hours Max. Marks: 80 Answer any Five questions All questions carry equal marks --1. For the QPSK modulator in the figure determine the I and Q bits for an input of a= + sinwctcoswct. Explain the functioning of this QPSK modulator.
+90o
Q
I
RBD
+vlogic1/2
a
Q-Product Detector
a coswct
LPF
uW
Q Channel Where a= (- sinwct+ coswct); RBD=Reactive Binary Data
Derive the output voltage relationship of an FSK modulator. Explain coherent demodulator and tribit.
3. a) b) c)
What are the characteristics of a serial interface? Define Baud rate What are the applications of USART?
4. a) b)
Explain the various parts of a terminal Explain how to construct the Hamming code for the bit sequence 10011101.
5. a) b) c)
What are the basic features of IBM’s bisync protocol? Explain bisync frame format with neat diagram Explain how bisync protocol is used for point-to-point communication.
6.
What is codes and combo chips? Explain the major function of combo chips and draw the block diagram of combo chip.
7.
Explain in detail statistical TDM. Compare it with synchronous TDM.
8.
Illustrate the point-to-point block transfer sequences in basic mode half duplex protocol. ###
Aj
nt
2. a) b)
Set No. Code No. 221901 II-B.Tech. II-Semester Examinations April/May, 2003
2
Time: 3 hours
.in
DATA COMMUNICATIONS (Electronics and Computer Engineering) Max. Marks: 80 Answer any Five questions All questions carry equal marks ---
1. For the QPSK modulator shown in the figure change the +900 phase shift network to -900 and construct the truth table, phasor diagram and constellation diagram. Explain its functioning.
fb /2
I channel
I-Balanced Modulator sinwct
logic 1=+1v
Input Buffer
1
logic 0=-1v Reference
0
Carier
900 phase shift
Oscillator
Bit Clock
+2
fb /2
sinwct logic 1=+1v
Q-Balanced fb /2 Modulator
logic 0=-1v
Linear Summer
BPF
QPSK output
+,-coswct
uW
Q channel
+,- sinwct
or ld
fb
Describe the bandwidth relationship of an FSK modulation scheme. Explain frequency deviation and modulation index for FSK modulation.
3.
Explain 2 wire and 4 wire operations of transmission mode in data communication with examples.
4.
Write short notes on the following a) CRT terminals b) PC terminals
5. a) b)
Discuss the merits and demerits of synchronous protocol. Explain the different fields of bisync frame. Mention the number of bits required for each field.
Aj
nt
2. a) b)
6.
Explain in detail line encoding with block diagram.
7.
Explain muldem, digital cross connect. Tabulate the digital signal, bit rate, channel capacities and service offered to various line types.
8.
Explain fully the full duplex point to point protocols. ###
Set No. Code No. 221901 II-B.Tech. II-Semester Examinations April/May, 2003
.in
DATA COMMUNICATIONS (Electronics and Computer Engineering) Max. Marks: 80 Answer any Five questions All questions carry equal marks ---
Time: 3 hours
For the QPSK modulator shown in the figure change the reference Oscillator to coswct and construct the truth table, phasor diagram and constellation diagram. Explain its functioning. I channel
fb
fb /2
logic 1=+1v
Input Buffer
1
logic 0=-1v Reference
0
Carier Oscillator
Bit Clock
+2
fb /2
sinwct logic 1=+1v logic 0=-1v
I-Balanced Modulator sinwct 900 phase shift
Q-Balanced Modulator
+,- sinwct
Linear Summer
BPF
QPSK output
+,-coswct
uW
Q channel fb /2
or ld
1.
3
Describe the difference between FSK and MSK modulation schemes.
3. a) b) c)
What is the use of transmission mode? Write the use of an acoustic coupler? What is the need for synchronization in data communication? Explain
4.
Explain the operation of different codes used in data communication.
5. a) b)
Explain briefly the different synchronous protocols in brief for data communication. Which mechanism bisync protocol uses for the flow control? Explain with an example.
Aj
nt
2.
6.
Describe the super frame format with block diagram. Why it is needed?
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