Digital Communications Multiple Choice Questions on “Trellis coded modulation”.
1. Adding improvement to the signal subset choice by starting with the densest possible lattice for the space is called as
A. Optimum signal constellation boundaries
B. Higher density lattice structures
C. Trellis coded modulation
D. None of the mentioned
Answer: B
Clarification: Higher density lattice structures are formed by adding improvement to the signal subset choice by starting with the densest possible lattice for the space.
2. Choosing a closely packed signal subset from any regular lattice or array of candidate points is called as
A. Optimum signal constellation boundaries
B. Higher density lattice structures
C. Trellis coded modulation
D. None of the mentioned
Answer: A
Clarification: Optimum signal constellation boundaries are obtained by choosing closely packed signal subset from any regular lattice or array of candidate points.
3. Trellis coded modulation uses
A. Non binary method
B. Uses redundant bits
C. No expansion of bandwidth
D. All of the mentioned
Answer: D
Clarification: Trellis coded modulation is a achieves error performance improvements without expansion of bandwidth. It uses redundant non binary modulation in combination with finite state machines.
4. In finite state machines, output is predicted using
A. Past output
B. Present input
C. Past output & Present input
D. None of the mentioned
Answer: C
Clarification: In finite state machines, the set of possible future outputs are predicted using present input and past output.
5. In TCM the signals are decoded using
A. Soft decision decoders
B. Hard decision decoders
C. Soft & Hard decision decoders
D. None of the mentioned
Answer: A
Clarification: In trellis coded modulation the noisy received signals are decoded using soft decision decoders.
6. Trellis coded modulation scheme
A. Has memory
B. Is memory-less
C. Needs more bandwidth
D. None of the mentioned
Answer: A
Clarification: Trellis coded modulation scheme has memory ( a finite state machine) such as the convolutional code.
7. In TCM channel capacity can be increased.
A. True
B. False
Answer: A
Clarification: In trellis coded modulation increase in channel capacity is achieved by signal set expansion.
8. Transmission bandwidth depends on
A. Rate of signalling
B. Density of signal points
C. Reduced distance
D. None of the mentioned
Answer: A
Clarification: Transmission bandwidth of non orthogonal signalling depends on rate of signalling and not on density of signal points in the constellation.
9. Which determines the error performance in TCM?
A. Reduced distance
B. Free distance
C. Bandwidth
D. None of the mentioned
Answer: B
Clarification: Free distance which is the minimum distance between members of set of allowed code sequences determines the error performance.
10. The TCM decoder uses
A. Minimum likelihood detector
B. Maximum likelihood detector
C. Does not use redundant bits
D. None of the mentioned
Answer: B
Clarification: The task of convolutional decoder is to estimate the path that the message had traversed through the encoding trellis using maximum likelihood detector.