Explore core concepts of cognitive radio and spectrum sensing with scenario-based questions designed to reinforce understanding of radio environments, signal detection, and interference management. This quiz targets principles and technical aspects critical for dynamic spectrum access and communication efficiency.
Which key function allows cognitive radio systems to dynamically access unused spectrum bands while minimizing interference to licensed users?
Explanation: Spectrum sensing is essential for cognitive radios to detect available spectrum and avoid interfering with licensed users. Frequency multiplexing is a method for transmitting multiple signals but does not enable dynamic access. Power amplification refers to boosting signal strength, unrelated to spectrum awareness. Channel coding is focused on error correction, not spectrum detection.
If a cognitive radio uses energy detection to sense the presence of primary users, what is a significant limitation of this method in practical environments?
Explanation: Energy detection measures the signal power but cannot identify the type of signal, making it susceptible to false alarms in the presence of noise. Requiring a pilot signal is more relevant to matched filter detection, not energy detection. The method functions at various frequencies, not just extremely high ones. Stating it always detects accurately is incorrect due to its lack of robustness in noisy environments.
A cognitive radio is operating in a band where a primary licensed user becomes active. What action should the cognitive radio take to avoid harmful interference?
Explanation: Vacating the channel is the standard way for cognitive radios to minimize interference with primary users as soon as their activity is detected. Increasing transmission power would worsen interference. Ignoring the licensed user is not permitted and may cause service disruption. Cognitive radios have no authority to request licensed users to change frequencies.
In spectrum sensing, what can cause a cognitive radio to wrongly detect a channel as occupied when it is actually free, a scenario known as a 'false alarm'?
Explanation: High levels of receiver noise can cause the sensing algorithm to interpret noise as a signal, leading to false alarms. Perfect channel estimation helps reduce errors rather than cause them. Constant power transmission refers to how the radio transmits, not how it senses. If spectrum monitoring were inactive, the radio would not make any detections at all.
A cognitive radio senses several empty frequency bands in an urban area. Which strategy allows it to select the best available channel for communication?
Explanation: Spectrum decision involves evaluating and selecting the most appropriate channel based on sensing results and communication needs. Spectral subspace analysis is a mathematical technique not commonly used directly for channel selection. Spectrogram inversion is not a standard procedure in cognitive radio. Spatial diversity enhances reliability over multiple antennas, not channel choice.