Problem:
While testing Wireless networks, people can receive different readings in terms of RSSI levels than those from both external and internal adapters.
Solution:
Signal strength measurements differ between Wi-Fi radios because RSSI is not standardized, and each chipset vendor implements its own scale, measurement method, and antenna design. Hardware differences, noise handling, and conversion to dBm all contribute to variations in reported values.
- RSSI is Vendor-Specific
- The IEEE 802.11 standard defines RSSI (Received Signal Strength Indicator) only as a relative measure, not an absolute one.
- Vendors like Intel, Broadcom, or Atheros use different scales (e.g., 0–60, 0–100, 0–255), so the same signal can appear stronger or weaker depending on the chipset.
- Conversion to dBm
- dBm is the standardized way to express signal strength, typically ranging from -30 dBm (excellent) to -90 dBm (poor).
- Radios convert RSSI to dBm differently, which explains why one device might show -65 dBm while another shows -70 dBm for the same access point.
- Antenna Design and Gain
- Antennas provide gain, direction, and polarization. A 5 dBi antenna will report stronger signals than a 2 dBi antenna in the same location.
- Even with identical radios, antenna differences can cause measurable variation.
- Number of Spatial Streams
- More spatial streams usually mean more antennas and each one measures its own RSSI.
- A 3×3 MIMO radio will have three RSSI values internally, often averaged or reported as the “signal strength.”
- Different vendors average, weight, or select the “best chain,” which can make multi-stream devices report stronger or weaker signals compared to single-stream radios.
- Multiple antennas can improve effective signal capture (array gain, diversity gain), so the reported RSSI may be higher or more stable compared to a single-stream device in the same spot.
- With multiple spatial streams, APs and clients can use transmit beamforming.
- This can concentrate energy toward the receiver, improving effective SNR (signal-to-noise ratio) and sometimes boosting reported RSSI.
- This can concentrate energy toward the receiver, improving effective SNR (signal-to-noise ratio) and sometimes boosting reported RSSI.
- More spatial streams usually mean more antennas and each one measures its own RSSI.
- Noise and Interference Handling
- Some radios factor in background noise or interference differently.
- Chipsets with advanced filtering may report lower RSSI in noisy environments compared to simpler radios.
- Measurement Point in the Signal Chain
- Radios can measure signal strength at different stages (intermediate frequency vs. baseband).
- This affects how the signal is sampled and reported, leading to discrepancies between devices.
- Implementation Differences
- Even when using the same chipset, vendors may implement firmware and drivers differently, which impacts how RSSI is calculated and displayed.
Conclusion:
In a nutshell, signal strength readings are relative, not absolute. Differences in chipset design, antenna gain, noise handling, and scaling explain why Wi-Fi radios report different values. We recommend customers use a Wi-Fi radio that is similar to the one used by end user client devices for site surveys, or a professional measurement tool like the AirCheck G3 which allows you to adjust the signal strength measured to match that of client devices.