Spectrum Sensing MCQs : This section focuses on the "Spectrum Sensing" in Cognitive Radio. These Multiple Choice Questions (MCQs) should be practiced to improve the Cognitive Radio skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.
Spectrum sensing is a critical issue of cognitive radio technology.
C. Can be true or false
D. Can not say
Explanation: True, Spectrum sensing is a critical issue of cognitive radio technology because of the shadowing, fading, and time-varying natures of wireless channels.
_____________ is the process of periodically monitoring a specific frequency band, aiming to identify presence or absence of primary users.
A. Spectrum Management
B. Spectrum Mobility
C. Spectrum sensing
D. Spectrum Sharing
Explanation: Spectrum sensing is the process of periodically monitoring a specific frequency band, aiming to identify presence or absence of primary users.
What is the purpose of in-band sensing?
A. Spectrum handoff
B. Sharing spectrum information
C. Sharing spectrum resources
D. Interference avoidance
Explanation: Spectrum sensing identifies unused spectrum holes that are available for transmission for cognitive radio users. During transmission, the cognitive radio users continue to monitor the spectrum band. They also sense other users of the primary network in order to avoid interference.
Spectrum sensing carried out during transmission is called ______________
A. full-band sensing
B. in-band sensing
C. out-band sensing
D. half-band sensing
Explanation: Spectrum sensing carried out during transmission is called in-band sensing.
Which among the following is not a transmission detection technique?
A. Matched filter detection
B. Energy detection
C. Cyclostationary detection
D. Interference based detection
Explanation: Transmission detection is based on the identification of weak signals sent by the primary transmitter obtained by the local observations of the xG users. Transmitter detection is also known as non-cooperative method. Interference based detection and cooperation detection are other spectrum sensing techniques.
Which among the following is not an operational unit in energy detection?
A. Squaring unit
D. Threshold device
Explanation: Energy detection consists of three operational units namely squaring device, integrator, and threshold device. The received signal energy is measured by squaring and integrating the received signal over an interval T. The output of the integrator is then evaluated by the threshold device to determine the existence of the primary user in the licensed spectrum.
Which among the following is achieved by coupling a modulated signal with a sine wave carrier?
Explanation: Modulated signals are coupled with sine wave carriers, hopping sequences, or cyclic prefixes to attain periodicity. The signals are regarded as cyclostationary due to periodic mean and autocorrelation.
What is the purpose of out-of-band sensing?
A. Fast switching
B. Fast routing
C. Fast discovery
D. Fast handoff
Explanation: Out-of-band sensing computes the time duration required by a cognitive radio user to detect a completely available spectrum band for transmission. Sensing order and stopping rule are factors that overlook out-of-band sensing.
Which among the following is not a disadvantage of cooperation detection?
A. Overhead traffic
B. Receiver uncertainty
C. Additional storage
D. Shadowing uncertainty
Explanation: The main drawback of cooperation detection is the increased strain on networks with limited resources as the number of operations and overhead traffic is increased. When the xG user communication range does not include the transmitter, interference is unavoidable as receiver information is unavailable. Receiver uncertainty is not solved by cooperation detection.
Cooperative spectrum sensing (CSS) is used to overcome the channel effects and exploit location diversity to detect even a weak primary signal.
C. Can be true or false
D. Can not say
Explanation: True, Cooperative spectrum sensing (CSS) is used to overcome the channel effects and exploit location diversity to detect even a weak primary signal.