Wireless Communication - Cognitive Radio — Test 1

Correct Answer: B. B. Host to host
Explanation: The four layers of the TCP/IP stack (also called the DoD model) are Application/Process, Host-to-Host, Internet, and Network Access. The Host-to-Host layer is equivalent to the Transport layer of the OSI model.

Correct Answer: D. D. Repair
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.

Correct Answer: D. D. Spectrum sharing
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.

Correct Answer: C. C. Vacate spectrum band
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.

Correct Answer: C. C. Match spectrum bands with user requirements
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.

Correct Answer: B. B. Amount of interference at the primary receiver
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.

Correct Answer: B. B. Path loss is increased
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.

Correct Answer: B. B. Modulation scheme
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.

Correct Answer: A. A. Selection of appropriate protocol
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.

Correct Answer: C. C. The duration over which the xg user can use the licensed spectrum band
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.