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Difficulty: Very hardTroubleshooting Wireless Connectivity and Signal Issues

A network architect is diagnosing severe performance degradation, high frame retransmission rates, and intermittent disconnections in a newly renovated logistics warehouse. An RF spectrum analyzer and site survey reveal two primary findings: (1) several 2.4 GHz access points (APs) are statically assigned to channels 1, 3, 7, and 11, and (2) high-power directional antennas mounted near metal support beams are creating significant delay spread at ground level. Which of the following statements accurately identify an underlying RF issue or a correct remediation step for this scenario? (Select TWO.)

  1. The APs operating on channels 3 and 7 induce adjacent-channel interference (ACI), which should be mitigated by reconfiguring all 2.4 GHz radios to use only non-overlapping channels 1, 6, and 11.Answer
  2. The signal reflections off metallic beams cause multipath distortion, which can be mitigated by adjusting AP placement, selecting appropriate antenna patterns, or enabling antenna diversity.Answer
  3. C
    Channel bonding adjacent 2.4 GHz channels 1 and 3 will eliminate frame retransmissions by doubling the channel bandwidth to 40 MHz40\text{ MHz}.
  4. D
    The observed packet loss and latency are indicative of a native VLAN mismatch on the trunk links connecting the APs to the switch infrastructure.

Answer

The correct statements identify that assigning channels 3 and 7 causes adjacent-channel interference (which requires reassigning radios to non-overlapping channels 1, 6, and 11) and that reflection off metal beams causes multipath distortion (which requires adjusting placement, antenna patterns, or utilizing antenna diversity).
The option addressing channel configuration is correct because using channels 3 and 7 in 2.4 GHz Wi-Fi introduces adjacent-channel interference; using only non-overlapping channels 1, 6, and 11 resolves this. The option addressing metal reflection is correct because metal structures create multipath signals and delay spread, which are mitigated by adjusting AP antenna positioning, diversity, or radiation patterns.

Step-by-Step Solution

1
Analyze the 2.4 GHz channel assignment findings.
Channels 1, 3, 7, and 11 overlap in frequency space. Channels 3 and 7 overlap partially with channels 1, 6, and 11, creating destructive adjacent-channel interference (ACI).
In the 2.4 GHz ISM band, each 20 MHz channel spaced 5 MHz apart overlaps with adjacent channels unless restricted to channels 1, 6, and 11 in North America/standard deployments.
2
Analyze the RF propagation issue near metallic beams.
Metallic surfaces reflect RF signals, causing multiple out-of-phase copies of the signal to reach the receiver at varying time intervals (delay spread), leading to multipath distortion.
High delay spread degrades signal quality (SNR) and causes symbols to overlap, resulting in corrupt frames and retransmissions.
3
Evaluate mitigation techniques for both findings.
Reassigning APs to non-overlapping channels 1, 6, and 11 resolves ACI. Adjusting AP placement, utilizing MIMO/antenna diversity, or optimizing directional coverage resolves multipath distortion.
These physical-layer RF remedies directly resolve the root causes revealed by the spectrum analyzer and site survey.

Key Concept

Wireless RF Interference and Multipath Propagation Troubleshooting
Estimated Time:2m 0s
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Topics

Troubleshooting Wireless Connectivity and Signal Issues

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