1. Which method should be implemented for reducing bandwidth?
a) Multilevel codes
b) Multilevel signalling
c) PAM
d) PDM
Explanation: The transmission bandwidth required for binary digital waveforms is large. To reduce the bandwidth, multilevel signalling method can be used
2. In M-ary PPM waveform, modulation is effected by
a) Delaying
b) Advancing
c) Delaying & Advancing
d) None of the mentioned
Explanation:In M-ary PPM waveform, modulation is effected by delaying or advancing pulse occurrence by an amount that corresponds to information symbol
3. For both PPM and PDM _______ is kept constant.
a) Amplitude
b) Time period
c) Frequency
d) Number of levels
Explanation:In PPM waveform delaying or advancing of pulse is done. In PDM the pulse width is varied. Thus in both the cases amplitude is maintained constant
4. The method in which small amount of controlled ISI is introduced into the data stream rather than trying to eliminate it completely is called as
a) Correlative coding
b) Duobinary signalling
c) Partial response signalling
d) All of the mentioned
Explanation: The interference at the detector can be cancelled out using these methods in which some controlled amount of ISI is introduced into the data stream
5. From digital filter we will get the output pulse as the _______ of the current and the previous pulse.
a) Summation
b) Difference
c) Product
d) Ratio
Explanation: The digital filter incorporates one digit delay and thus it adds the incoming pulse with the value of the previous pulse
6. In duobinary signalling method, for M-ary transmission, the number of output obtained is
a) 2M
b) 2M+1
c) 2M-1
d) M2
Explanation:In duobinary coding, the number of output obtained for M-ary transmission is 2M-1
7. The method using which the error propagation in dubinary signalling can be avoided is
a) Filtering
b) Precoding
c) Postcoding
d) None of the mentioned
Explanation: In duobinary signalling method if one error occurs it repeats everywhere through out the next steps. To avoid this precoding method can be used
8. In precoding technique, the binary sequence is _____ with the previous precoded bit.
a) And-ed
b) Or-ed
c) EXOR-ed
d) Added
Explanation: To avoid error propogation precoding method is used. In this each bit is encoded individually without having any effect due to its prior bit or decisions
9. The duobinary filter, He (f) is called as
a) Sine filter
b) Cosine filter
c) Raised cosine filter
d) None of the mentioned
Explanation: The transfer function is 2T cos(πfT) which is called as cosine filter
10. The method which has greater bandwidth efficiency is called as
a) Duobinary signalling
b) Polybinary signalling
c) Correlative coding
d) All of the mentioned
Explanation: If more than three levels are introduced in duobinary signalling technique the bandwidth efficiency increases This method is called as polybinary signalling