CWT Wireless Standards & Radio Frequency Fundamentals 3 — Questions and Answers
Question 1: What is the maximum number of spatial streams supported by 802.11ac Wave 2?
- 2
- 4
- 8 (Correct answer)
- 16
Correct answer: 8
802.11ac Wave 2 supports up to 8 spatial streams using MU-MIMO, allowing simultaneous transmission to multiple clients.
Question 2: In the 5 GHz band, what does the acronym DFS stand for?
- Dynamic Frequency Shifting
- Dynamic Frequency Selection (Correct answer)
- Distributed Frequency Synchronization
- Direct Frequency Scanning
Correct answer: Dynamic Frequency Selection
Dynamic Frequency Selection (DFS) is a mechanism that requires Wi-Fi devices to detect radar signals and switch channels to avoid interference with radar systems.
Question 3: Which RF phenomenon occurs when a signal travels two different paths and the delayed copy destructively interferes with the primary signal?
- Refraction
- Scattering
- Multipath fading (Correct answer)
- Diffraction
Correct answer: Multipath fading
Multipath fading occurs when reflected or scattered copies of a signal arrive at the receiver out of phase, causing destructive interference and signal degradation.
Question 4: What is the guard interval in OFDM, and why is it used?
- A frequency gap between subcarriers to prevent overlap
- A time gap between symbols to prevent intersymbol interference from multipath (Correct answer)
- A power reduction period between transmissions
- A cyclic prefix that enables synchronization only
Correct answer: A time gap between symbols to prevent intersymbol interference from multipath
The guard interval is a brief silent period inserted between OFDM symbols to allow multipath echoes to die out before the next symbol is received, preventing ISI.
Question 5: Which regulatory body allocates RF spectrum and sets EIRP limits for unlicensed devices in the United States?
- IEEE
- Wi-Fi Alliance
- FCC (Correct answer)
- IETF
Correct answer: FCC
The Federal Communications Commission (FCC) regulates RF spectrum allocation and establishes maximum EIRP limits for unlicensed devices in the US under Part 15 rules.
Question 6: What Wi-Fi generation corresponds to the IEEE 802.11ac standard?
- Wi-Fi 4
- Wi-Fi 5 (Correct answer)
- Wi-Fi 6
- Wi-Fi 6E
Correct answer: Wi-Fi 5
The Wi-Fi Alliance designated 802.11ac as Wi-Fi 5, which operates in the 5 GHz band and supports MU-MIMO and up to 160 MHz channels.
Question 7: What is the purpose of Transmit Power Control (TPC) in wireless networks?
- To boost transmit power to overcome interference
- To dynamically reduce transmit power to minimize interference with adjacent systems (Correct answer)
- To synchronize power levels across all clients
- To enable fast roaming by lowering power thresholds
Correct answer: To dynamically reduce transmit power to minimize interference with adjacent systems
TPC allows devices to reduce their transmit power when maximum power is not needed, reducing co-channel interference and meeting regulatory requirements on DFS channels.
CWT Wireless Standards & Radio Frequency Fundamentals 3
What is the maximum number of spatial streams supported by 802.11ac Wave 2?