CWS RF Behavior & Signal Propagation 2 — Questions and Answers
Question 1: Which phenomenon causes a wireless signal to bend around corners or obstacles?
- Reflection
- Refraction
- Diffraction (Correct answer)
- Scattering
Correct answer: Diffraction
Diffraction allows RF signals to bend around the edges of obstacles, enabling coverage in areas not in direct line of sight.
Question 2: What is the Fresnel zone primarily used to evaluate in wireless deployments?
- Antenna gain
- Path clearance for line-of-sight links (Correct answer)
- Channel width selection
- Transmit power levels
Correct answer: Path clearance for line-of-sight links
Fresnel zones define elliptical regions around a line-of-sight path where obstructions can cause signal degradation due to phase cancellation.
Question 3: Multipath propagation in an indoor environment most commonly results in which condition?
- Increased transmit power
- Signal fading and intersymbol interference (Correct answer)
- Higher antenna gain
- Reduced frequency reuse
Correct answer: Signal fading and intersymbol interference
Multipath causes copies of the signal to arrive at different times, leading to fading and intersymbol interference that degrades throughput.
Question 4: In free-space path loss calculations, doubling the distance between transmitter and receiver increases path loss by approximately how many dB?
- 3 dB
- 6 dB (Correct answer)
- 10 dB
- 20 dB
Correct answer: 6 dB
Free-space path loss follows an inverse-square law, so doubling distance quadruples path loss, which is a 6 dB increase.
Question 5: Which 802.11 technique was specifically designed to mitigate multipath-induced intersymbol interference?
- DSSS
- FHSS
- OFDM guard interval (cyclic prefix) (Correct answer)
- MIMO beamforming
Correct answer: OFDM guard interval (cyclic prefix)
The OFDM cyclic prefix (guard interval) absorbs multipath delay spread, preventing symbols from overlapping at the receiver.
Question 6: When an RF signal passes from a less dense medium into a denser medium at an angle, it changes direction. This behavior is called:
- Reflection
- Scattering
- Diffraction
- Refraction (Correct answer)
Correct answer: Refraction
Refraction is the bending of an RF wave as it passes between media with different propagation velocities, such as air and glass.
Question 7: A 5 GHz signal experiences greater free-space path loss than a 2.4 GHz signal at the same distance primarily because:
- 5 GHz uses wider channels
- Higher frequency signals have shorter wavelengths and higher path loss per unit distance (Correct answer)
- 5 GHz antennas have lower gain
- Regulatory power limits are lower at 5 GHz
Correct answer: Higher frequency signals have shorter wavelengths and higher path loss per unit distance
Free-space path loss increases with frequency; 5 GHz signals have shorter wavelengths, resulting in higher path loss compared to 2.4 GHz at equal distances.
CWS RF Behavior & Signal Propagation 2
Which phenomenon causes a wireless signal to bend around corners or obstacles?