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Difficulty: HardTroubleshooting Wireless Connectivity and Signal Issues

A network technician is troubleshooting a point-to-point wireless bridge spanning 250 meters between two corporate buildings. Signal strength readings indicate a strong Received Signal Strength Indicator (RSSI) of -51 dBm, but the link suffers from high packet corruption, fluctuating bit rates, and intermittent dropouts whenever large cargo trucks cross the intervening parking lot. Which of the following is the most likely cause of this wireless performance issue?

  1. Multipath fading caused by RF reflections off moving vehicles arriving out of phase at the receiving antenna.Answer
  2. B
    Adjacent-channel overlap from neighboring indoor 2.4 GHz access points operating on channels 1, 2, and 3.
  3. C
    A failure of the wireless bridge interfaces to renew their assigned APIPA addresses under heavy load.
  4. D
    A Ethernet speed and duplex mismatch on the cable connecting the switch to the PoE injector.

Answer

Multipath fading caused by RF reflections off moving vehicles arriving out of phase at the receiving antenna is the primary cause of the signal degradation.
Multipath propagation occurs when RF signals take multiple paths from transmitter to receiver due to reflection off metallic surfaces like trucks. When these reflected signals arrive slightly out of phase with the direct signal, they cause destructive interference (multipath fading) and inter-symbol corruption even when overall RSSI appears high.

Step-by-Step Solution

1
Analyze diagnostic indicators
Strong RSSI (-51 dBm) confirms adequate transmission power and basic line of sight, but high frame corruption indicates physical layer RF distortion.
High signal power paired with low throughput or packet loss points toward signal quality issues (SNR/Interference) rather than attenuation.
2
Evaluate environmental variables
Intermittent corruption specifically coincides with large metal vehicles entering the path between buildings.
Metallic surfaces serve as prominent reflectors for radio waves, splitting the transmitted signal into multiple paths.
3
Identify the RF phenomenon
Reflected signals arrive at the receiving antenna milliseconds after the direct line-of-sight signal, creating phase interference.
When reflected signals arrive out of phase with the main signal, vector addition causes signal cancellation and inter-symbol interference (multipath fading).

Key Concept

Multipath Fading and RF Reflection in Point-to-Point Wireless Links
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Topics

Troubleshooting Wireless Connectivity and Signal Issues

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