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Difficulty: HardWireless Network Deployment and Standards

During a wireless network site audit of an enterprise facility, a network technician discovers that four access points (APs) installed sequentially along a long corridor are operating on 2.4 GHz channels 1, 4, 8, and 11, respectively. Client devices connected near the middle of the corridor experience high frame retransmission rates and degraded throughput despite indicating strong signal strength. Which modification to the wireless spectrum configuration will best eliminate adjacent channel interference while preserving continuous coverage?

  1. Reassign the access points sequentially to channels 1, 6, 11, and 1, while adjusting transmit power to control co-channel interference between the non-adjacent channel 1 cells.Answer
  2. B
    Reassign the access points to channels 1, 4, 7, and 10 to establish uniform three-channel numerical spacing across the available 2.4 GHz frequency range.
  3. C
    Enable 40 MHz channel bonding across all four access points to force dynamic frequency selection and override spectral overlap.
  4. D
    Increase the transmit power on the access points configured for channels 4 and 8 to override background radio frequency noise generated by channels 1 and 11.

Answer

Reassign the access points sequentially to channels 1, 6, 11, and 1, while adjusting transmit power to control co-channel interference between the non-adjacent channel 1 cells.
The 2.4 GHz Wi-Fi spectrum only contains three non-overlapping 20 MHz channels: 1, 6, and 11. Configuring access points on overlapping channels like 4 and 8 results in adjacent channel interference (ACI), which cannot be effectively negotiated by CSMA/CA mechanism and leads to frame corruption and retransmissions. Reallocating the access points to channels 1, 6, 11, and repeating channel 1 at the far end with tuned transmit power eliminates ACI and minimizes co-channel interference.

Step-by-Step Solution

1
Analyze the 2.4 GHz channel plan and identify the cause of degradation.
Channels 1, 4, 8, and 11 overlap. Each 20 MHz channel occupies a 22 MHz spectral mask spanning 5 channel numbers. Channels 4 and 8 overlap with channels 1, 6, and 11.
Adjacent channel interference (ACI) prevents Wi-Fi devices from performing standard CSMA/CA contention detection, leading to packet collisions and high retransmissions.
2
Determine the standard non-overlapping channel scheme for 2.4 GHz deployments.
The only non-overlapping 20 MHz channel combination in North America/regulatory domains is channels 1, 6, and 11.
These channels have at least 25 MHz separation between center frequencies, preventing spectral overlap.
3
Formulate the remediation plan for a four-AP corridor deployment.
Assign channels 1, 6, 11, and reuse channel 1 on the furthest AP (1, 6, 11, 1). Lower transmit power on the channel 1 APs to limit cell overlap.
Reusing channel 1 with proper power calibration creates manageable co-channel interference (CCI) rather than destructive adjacent channel interference (ACI).

Key Concept

2.4 GHz Non-Overlapping Channel Assignment and ACI vs CCI Mitigation
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Topics

Wireless Network Deployment and Standards

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