// reference · rssi / snr thresholds
RSSI & SNR Threshold Reference
Minimum RSSI and SNR required to sustain each MCS — for all four 802.11 generations. The numbers you need when reading a PCAP and asking "should this client be at MCS 7 or MCS 9?"
— Shankar K. · Values are typical chipset thresholds; vendor-specific ±2–3 dB variation expected
// signal quality quick check
SNR
Maximum stable MCS
-95 dBmPoorFairGoodExcellent-40 dBm
// application-level rssi thresholds
| Application | Min RSSI | Min SNR | Why |
|---|---|---|---|
| Basic internet browsing | -80 dBm | 10 dB | MCS 0-2 sufficient. Tolerates retries. Not latency-sensitive. |
| Video streaming (HD) | −75 dBm | 15 dB | Needs sustained ~10 Mbps. MCS 3-4 minimum. Buffer hides short dropouts. |
| Video conferencing (Zoom/Teams) | −70 dBm | 20 dB | Bidirectional, latency-sensitive. Retries cause pixelation and audio cuts. |
| VoIP / voice calls | −67 dBm | 25 dB | Most demanding. Needs MCS 5+ consistently. Any retry causes audible glitch. |
| IoT / sensors | −80 dBm | 10 dB | Low data rate but needs reliable delivery. Power management (TWT) matters more than throughput. |
| High-density enterprise | −65 dBm | 25 dB | Design for MCS 7+ at cell edge. High user count needs consistent airtime per client. |
| Real-time location (RTLS) | −75 dBm | 15 dB | Needs 3+ AP visibility. Accuracy degrades below -75 dBm. RSSI consistency matters more than peak. |
// field notes from 15 years of Wi-Fi qualification
FCS errors at high RSSI
If you see FCS errors with RSSI -55 dBm or better, the problem is NOT signal strength — it's co-channel interference. Another AP on the same channel is corrupting frames. Engineers misdiagnose this as range problems constantly.
The sticky client trap
A client showing -75 dBm connected to AP-1 while AP-2 is at -60 dBm = 15 dB better signal ignored. Check retry rate — if retries are high at -75 dBm, the client is hurting itself and everyone else on that channel.
MCS mismatch in enterprise
A client connected at MCS 0 (-82 dBm floor) in a conference room where the AP is 5 metres away is a driver or AP configuration issue — not RF. In gateway qualification, I see this with specific driver versions that don't renegotiate rate after initial low-SNR association.
Noise floor variation
Noise floor varies by channel. 2.4 GHz channels 1, 6, 11 often have -85 to -90 dBm floor. Noisy 2.4 GHz environments can push noise to -80 dBm — meaning -70 dBm RSSI only gives you 10 dB SNR, not 20. Always check actual noise floor, not assumed.
See RSSI per frame in a real PCAP
WiFi Analyser reads radiotap.dbm_antsignal per frame and correlates RSSI to MCS index automatically.
// share this page
// also on this site
SK
— Shankar K., Wi-Fi engineer, Irving TX
Building WiFi Analyser V2 · CWNA-109 in progress · one post every two weeks
Building WiFi Analyser V2 · CWNA-109 in progress · one post every two weeks
// leave a comment