# Cognitive Radio Questions and Answers – Next Generation Wireless Network – Spectrum Awareness – 1

This set of Cognitive Radio Multiple Choice Questions & Answers (MCQs) focuses on “Next Generation Wireless Network – Spectrum Awareness – 1”.

1. Which among the following is not an objective of cognitive radio?
a) Adapt to the available spectrum
b) Minimize radio presence in the spectrum environment
c) Maximize radio presence for the networks
d) Exploit spectrum holes

Explanation: The objectives of the cognitive radio are to minimize the radio presence in a network while gathering data about the spectrum from the spectrum environment and to adapt to the available spectrum determined from the gathered data. The dynamic characteristics of the cognitive radio rely on its ability to sense the propagation conditions.

2. Which among the following is a definition of spectrum efficiency?
a) Number of bits per Hertz of bandwidth
b) Number of bauds per Hertz of bandwidth
c) Number of Hertz per bit of symbol sequence
d) Number of Hertz per bit of symbol sequence

Explanation: Modulation designers describe spectrum efficiency in terms of the number of bits per Hertz of bandwidth. It is used as a metric for measuring the performance of modulation techniques.

3. Which among the following outcome occur on increasing the energy per bit exponentially as per Shannon limit?
a) Radiated spectral energy increases at the second power of the spectral information density
b) Radiated spectral energy increases at the third power of the spectral information density
c) Spectral information density increases at the third power of the radiated spectral energy
d) Spectral information density increases at the second power of the radiated spectral energy

Explanation: Shannon limit specifies the maximum rate at which communication can be carried out without error in a channel with a given bandwidth. Shannon limit supports a claim that spectrum efficiency of infinite bits per Hertz can be achieved by increasing energy per bit exponentially. This results in the increase of radiated spectral energy at the third power of spectral information density.

4. Which among the following is a traditional method employed for effective use of spectrum?
a) Minimization of nodes per second
b) Maximization of nodes per second
c) Maximization of bits per Hz
d) Minimization of bits per Hz

Explanation: Spectrum efficiency metrics of traditional digital communication is simple as it involves measuring only the number of bits per Hz. When the number of bits per Hz is maximized, a minimal amount of spectrum is occupied. However defining spectrum metrics for cognitive radio is difficult as it includes the area of propagation in addition to the amount of spectrum.

5. Which among the following is an appropriate unit for spectrum usage in cognitive radio?
a) Bits per unit area
b) Noise per unit area
c) Noise temperature per unit area
d) Symbols per unit area

Explanation: Spectrum usage in the cognitive radio includes the area of propagation along with the amount of spectrum used. Hence the number of bits per unit area is an appropriate unit for spectrum usage in cognitive radio. This necessitates the inclusion of propagation in the Shannon limit.
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6. Which among the following is a not consequence of increasing modulation depth?
a) Increase energy need
b) Increase spectral efficiency
c) Reduce effective spectrum usage of other users of the spectrum
d) Reduced noise floor

Explanation: Modulation depth provides the degree of difference between a modulated signal and an unmodulated signal. The increase of modulation depth is a poor solution for effective spectrum usage as it increases the energy needs of the operation. It affects the operation of other spectrum users as it results in the increase of noise floor or it precludes the operation at quickly increasing radii from the transmitter.

7. Which among the following phenomenon considers the operation of other users of the spectrum?
a) Spectrum efficiency
b) Spectrum reuse
c) Channel capacity
d) Signal energy

Explanation: Spectrum reuse is a critical phenomenon that includes the optimal operation of other users of the spectrum through spectrum sharing. It involves reporting the information of spectrum usage to spectrum broker and distributing spectrum usage information to other nodes.

8. Which among the following is a common factor between peer to peer cognitive radio and a digital radio?
a) Automation
b) Inbuilt rules
c) Time cycle
d) Local operation

Explanation: Peer to peer cognitive radio rely on spectrum usage information from local neighbours but is mostly controlled by a set of comprehensive rules which are provided by the manufacturer. This reduces the amount of overhead in communication but leads to reduced efficiency. Decisions are taken by combining local spectrum awareness and inbuilt rules.

9. Which among the following is not a prerequisite for cooperative sensing?
b) Knowledge of spectrum environment
c) Knowledge of limits of transmission parameters
d) Central entity

Explanation: Cooperative spectrum sharing involves sharing spectrum usage and noise information to other nodes of the spectrum. This mode considers the operation of other spectrum users thus raising the overall spectrum efficiency of the network. It requires non-corrupt neighbouring radios, knowledge of spectrum environment, understanding of limits imposed on transmission parameters, and transparent sharing of spectrum information by transmitters.

10. Which among the following institution introduced interference temperature as a metric for interference?
a) Federal Communication Commission
b) American National Standards Institute
c) International Standards Organization
d) British Standards Institute

Explanation: Federal Communication Commission introduced interference temperature as a metric for modeling interference at the primary user produced by the secondary user. It is a measure of RF power generated by undesired transmitters and noise sources that are present in the receiver system per unit of bandwidth.

11. Diffracted propagation undergoes attenuation at the rate of the third power of distance.
a) True
b) False

Explanation: Cognitive radio shifts communication from direct propagation to diffracted propagation. Diffracted propagation undergoes attenuation at the rate of the fourth power of distance. It hinders the ability of the radio to sense, calculate interference, and evaluate the outcome of communication.

12. Which among the following is false about multiple input, multiple output scheme?
a) MIMO generates multiple orthogonalized channel
b) Channel awareness is used to design link
c) Coverts multiple path into multiple channels
d) Eliminates multiple path

Explanation: Multiple input, multiple output is a technique that introduces multiple antennas at the transmitter and the receiver generating several paths for transmission. MIMO introduces channel awareness on an architectural level and is employed in the generation of links and topology. It utilizes multipath and converts multiple paths into multiple channels.

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