CWDP Channel Planning and RF Design 2 — Questions and Answers
Question 1: What channel width is recommended for high-density enterprise WLAN deployments to maximize the number of available non-overlapping channels in the 5 GHz band?
- 80 MHz
- 40 MHz
- 20 MHz (Correct answer)
- 160 MHz
Correct answer: 20 MHz
20 MHz channels maximize the number of non-overlapping channels available, which is critical in high-density environments to reduce co-channel interference.
Question 2: When using 40 MHz channel bonding in the 5 GHz band, what is the effect on the number of available non-overlapping channels compared to 20 MHz channels?
- It doubles the number of available channels
- It has no impact on channel count
- It roughly halves the number of available channels (Correct answer)
- It increases channels by one-third
Correct answer: It roughly halves the number of available channels
Bonding two 20 MHz channels into a 40 MHz channel consumes twice the spectrum, cutting the number of non-overlapping channel pairs to roughly half the 20 MHz count.
Question 3: What is the purpose of DFS (Dynamic Frequency Selection) in the 5 GHz band?
- To boost throughput for latency-sensitive applications like VoIP
- To detect radar systems and move 802.11 devices off channels that interfere with them (Correct answer)
- To automatically switch devices between 2.4 GHz and 5 GHz bands
- To enable simultaneous dual-band operation on a single radio
Correct answer: To detect radar systems and move 802.11 devices off channels that interfere with them
DFS is a regulatory requirement that forces 802.11 devices to detect radar signals on certain 5 GHz channels and vacate those channels to avoid interfering with radar systems.
Question 4: Which hexagonal cell channel reuse pattern is standard for 2.4 GHz WLAN deployments?
- Channels 1, 4, and 8 in a triangular pattern
- Channels 1, 6, and 11 in a honeycomb pattern (Correct answer)
- Channels 1, 5, and 9 in a linear pattern
- Channels 1, 7, and 13 in a grid pattern
Correct answer: Channels 1, 6, and 11 in a honeycomb pattern
A hexagonal cell pattern using channels 1, 6, and 11 — the only three non-overlapping 2.4 GHz channels in the US — is the standard approach for minimizing co-channel and adjacent-channel interference.
Question 5: In RF design, what is the 'cell edge' and why does it matter?
- The physical wall boundary of the building envelope
- The outer boundary of an AP's coverage area where signal strength approaches the minimum usable threshold (Correct answer)
- The geometric center of an AP's radiation pattern
- The area of peak signal strength directly below the AP
Correct answer: The outer boundary of an AP's coverage area where signal strength approaches the minimum usable threshold
The cell edge is where RF signal strength drops to the minimum acceptable level; designing consistent cell edges ensures overlap between APs and reliable roaming.
Question 6: What is the recommended minimum RSSI at the cell edge for enterprise voice (VoWLAN) applications according to CWDP design guidelines?
- -50 dBm
- -67 dBm (Correct answer)
- -80 dBm
- -90 dBm
Correct answer: -67 dBm
-67 dBm is the widely accepted minimum RSSI threshold at the cell edge for voice-grade WLAN, ensuring sufficient signal quality for low-latency, low-jitter voice traffic.
Question 7: Which channel planning approach is preferred in high-density venues such as conference centers or stadiums?
- 2.4 GHz-only deployment for maximum range
- All APs set to the same channel for seamless roaming
- 5 GHz-only deployment with 20 MHz channels to maximize non-overlapping channel count (Correct answer)
- Mixed 2.4/5 GHz with 80 MHz channel bonding throughout
Correct answer: 5 GHz-only deployment with 20 MHz channels to maximize non-overlapping channel count
5 GHz-only with 20 MHz channels provides the most non-overlapping channels and avoids the congested 2.4 GHz band, which is essential when many APs and clients coexist in a small area.
CWDP Channel Planning and RF Design 2
What channel width is recommended for high-density enterprise WLAN deployments to maximize the number of available non-overlapping channels in the 5 GHz band?