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

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

1. Which among the following is not considered for associating a cognitive radio user to an unused spectrum band?
a) Time-varying radio environment
b) Bandwidth
c) QoS requirement
d) Application policies
View Answer

Answer: d
Explanation: The various characteristics of the unused spectrum bands determined during spectrum sensing depend on the time-varying radio environment, operating frequency, bandwidth, and quality of service requirements of the cognitive radio user. Spectrum management is required to correctly associate a user to a compatible spectrum band among all available spectrum bands in xG networks.

2. What among the following is not a function of spectrum management?
a) Sensing
b) Decision
c) Mobility
d) Repair
View Answer

Answer: d
Explanation: The major functions of spectrum management are spectrum sensing, spectrum analysis, and spectrum decision-making. Spectrum sharing and spectrum mobility are also included in the management framework. Every function operates over all layers of the OSI model except sensing which is implemented only in the physical layer.

3. Which among the following functions prevent collision?
a) Spectrum analysis
b) Spectrum decision
c) Spectrum mobility
d) Spectrum sharing
View Answer

Answer: d
Explanation: In the unlicensed portion of the spectrum, cognitive radio users have equal access to the spectrum and attempt to access the spectrum simultaneously. Spectrum sharing coordinates the network access such that collision is avoided in overlapping portions of the spectrum.

4. What is the function of spectrum mobility?
a) Detect spectrum holes
b) Gather information about available spectrum bands
c) Vacate spectrum band
d) Monitor spectrum band
View Answer

Answer: c
Explanation: The cognitive radio users only have temporary access to the unused spectrum in the licensed band. If the primary user demands access, the spectrum mobility function of the spectrum management framework intervenes and transfers the cognitive radio user to another vacant position.

5. What is the function of the spectrum analysis unit?
a) Detect spectrum holes
b) Prevent collision between multiple users
c) Match spectrum bands with user requirements
d) Listen for the arrival of the primary user
View Answer

Answer: c
Explanation: Spectrum analysis defines the characteristics of the spectrum bands and verifies whether the characteristics meet the user requirements. Interference level, channel error rate, link-layer delay, holding time, and path loss are few of defining parameters of a spectrum band.
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6. Which parameter can be used to compute the permissible power of xG users?
a) Distance between the primary transmitter and xG user
b) Amount of interference at the primary receiver
c) Amount of interference at xG user
d) Distance between the primary receiver and xG user
View Answer

Answer: b
Explanation: Channel capacity can be estimated by determining the permissible power of an xG user. The permissible power is computed by determining the amount of interference at the primary receiver. The amount of interference sometimes depends on the number of users in the spectrum.

7. Which among the following statements is false about the outcome of increasing transmission power?
a) Transmission range at higher frequencies is maintained
b) Path loss is increased
c) Interference is increased
d) Transmission range at lower frequencies is maintained
View Answer

Answer: b
Explanation: Path loss is proportional to the operating frequency. Hence, transmission range gradually reduces with an increase in frequency when the transmission power is not modified. If transmission power is increased, the path loss is decreased with an increase in the amount of interference.

8. Which among the following factors affect the error rate?
a) Encoding techniques
b) Modulation scheme
c) Channel capacity
d) Access techniques
View Answer

Answer: b
Explanation: Wireless link errors are parameters of importance in characterizing the spectrum band. The modulation scheme and the amount of interference in the spectrum band influence the error rate. Wrongful sensing decisions are also a contributing factor to the high error rate.

9. What is the primary cause of the link-layer delay?
a) Selection of appropriate protocol
b) Selection of routing path
c) Packet generation
d) Frame generation
View Answer

Answer: a
Explanation: Each spectrum band is assigned a different protocol with respect to the interference level, path loss, and wireless link errors of the band. The link-layer packet transmission delay differs with different protocols.

10. What is holding time?
a) The duration required to identify a spectrum hole
b) The duration available after the arrival of the primary user to vacate the spectrum band
c) The duration over which the xG user can use the licensed spectrum band
d) The duration over which the xG user can use the unlicensed spectrum band
View Answer

Answer: c
Explanation: Holding time refers to the period over which the xG user can occupy the licensed spectrum band before the arrival of the primary user. High holding time ensures high quality. Statistical handoff patterns are used to construct xG networks with longer holding time.

11. Which among the following is a challenge for spectrum management?
a) Asynchronous sensing
b) Multiple spectrum band operation
c) Availability of non-contiguous spectrum bands
d) Reconfiguration
View Answer

Answer: d
Explanation: Transmission parameters of a radio should be reconfigurable for effective operation in certain spectrum bands. For example, if the signal to noise cannot be modified, then the bit error rate can be altered to maintain the channel capacity by employing adaptive modulation techniques.

12. Which among the following terms should replace the labels ‘A’ and ‘B’ in the diagram?
Find the link-layer delay from the given diagram
a) A – Link layer delay, B – Scheduling Information
b) A – Link layer establishment, B – Spectrum broker
c) A – Scheduling information, B – Link layer delay
d) A – Spectrum broker, B – Link layer establishment
View Answer

Answer: a
Explanation: Link-layer delay is one of the defining parameters of quality of service. Various link layer protocols suitable for different path loss, wireless link error, and interference are available. Link layer packet transmission delay changes with respect to the selected protocol. Scheduling information ensure fair sharing of spectrum resources in the unlicensed spectrum band.

Sanfoundry Global Education & Learning Series – Cognitive Radio.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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