# Digital Communications Questions and Answers – Waveform Coding

This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Waveform Coding”.

1. Channel coding relates to area such as
a) Waveform coding
b) Structured sequence
c) Waveform coding & Structured sequence
d) None of the mentioned

Explanation: Channel coding can be partitioned into two area of studies, one is waveform coding or signal design and the other is a structured sequence or structured redundancy.

2. Examples of structured sequences are
a) Block codes
b) Convolutional codes
c) Turbo codes
d) All of the mentioned

Explanation: Some examples of structured sequence or structured redundancy codes are block codes, convolutional codes and turbo codes.

3. Antipodal signals are
a) Mirror images
b) 1800 apart
c) One is negative of the other
d) All of the mentioned

Explanation: Antipodal signals are mirror images, one is negative of the other and they are 1800 apart.

4. Orthogonal vectors are
a) Perpendicular to each other
b) Their dot product must be zero
c) One signal cannot interfere with the other
d) All of the mentioned

Explanation: Orthogonal signals are perpendicular to each other, the inner or dot product between those two signals must equal zero, one vector has zero projection over the other because they do not share same signal space.

5. In orthogonal signalling as k increase there is
a) Improved error performance
c) Improved bandwidth
d) None of the mentioned

Explanation: In orthogonal signalling as k increases there is improved error performance or a reduction in required Eb/N0 at the expense of bandwidth.
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6. In non orthogonal signalling as k increases there is
b) Improved bandwidth efficiency
c) Increase in required Eb/N0
d) All of the mentioned

Explanation: Non orthogonal signalling manifests improved bandwidth efficiency at the expense of degraded error performance and increases in required Eb/N0.

7. In orthogonal signal, all cross correlation coefficients are
a) One
b) Zero
c) Negative
d) None of the mentioned

Explanation: In orthogonal set all cross correlation coefficients can be made zero.

8. The smaller the cross correlation, the ______ is the distance between the signal vectors.
a) More
b) Less
c) Double
d) Half

Explanation: The cross correlation is the measure of distance between two vectors. The smaller the cross correlation value the greater the distance between the two vectors.

9. Hadamard matrix is given as
a)

```H2 =  H1 H1
H1 H1```

b)

```H2 =  H1 H1
H1'H1```

c)

```H2 =  H1 H1
H1 H1'```

d)

```H2 =  H1'H1
H1 H1```
Explanation: We can construct a code-word set Hk of dimension 2k*2k called a Hadamard matrix.

10. Biorthogonal set consists of
a) Orthogonal signals
b) Antipodal signals
c) Combination of orthogonal and antipodal
d) None of the mentioned

Explanation: The biorthogonal set consists of a combination of both orthogonal and antipodal signals.

11. Which codes perform better?
a) Orthogonal
b) Biorthogonal
c) Orthogonal & Biorthogonal
d) None of the mentioned

Explanation: Since the antipodal vector has a better distance property than the orthogonal signals, biorthogonal codes perform better than the orthogonal codes.

12. Biorthogonal codes needs ________ bandwidth as orthogonal codes.
a) Equal
b) Double
c) Half
d) Triple

Explanation: Biorthogonal codes perform better than the orthogonal codes and it needs only half the bandwidth as orthogonal codes.

13. Transorthogonal code is obtained by
a) Deleting last digit of each orthogonal codeword
b) Deleting first digit of each orthogonal codeword
c) Doubling each digit of orthogonal codeword
d) Taking negative of each digit of orthogonal codeword

Explanation: A code generated from an orthogonal set by deleting the first digit of each codeword is called as transorthogonal code or simplex code.

14. Which code requires minimum Eb/N0?
a) Orthogonal
b) Biorthogonal
c) Simplex
d) All of the mentioned

Explanation: A simplex code represents the minimum energy equivalent and it requires minimum Eb/N0 for a specified symbol error rate.

Sanfoundry Global Education & Learning Series – Digital Communications.

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