RSSI

RSSI indicates the strength of the signal arriving at a receiver. IEEE 802.11 originally defined it as a vendor-specific, unitless index, but today most devices report it directly in dBm (decibels relative to one milliwatt). Values are negative and grow stronger towards zero. A −50 dBm signal is 100 times stronger than a −70 dBm signal.

Common Wi-Fi reference values are −30 to −50 dBm excellent and −50 to −67 dBm good, with −67 dBm a typical minimum target for voice and video calls. Around −70 dBm is enough for basic browsing but speeds drop, and at −80 dBm and below connections become unstable. On PTP and PTMP links, −45 to −65 dBm is generally targeted for high-order modulation.

RSSI alone does not describe link quality. What really matters is SNR, the ratio of signal to the ambient noise floor, or SINR, which also accounts for interference. A −65 dBm signal over a −95 dBm noise floor gives 30 dB SNR, enough for high modulation rates. The same signal may be inadequate where interference lifts the noise floor to −75 dBm. Because vendors calculate RSSI differently, be careful when comparing values across brands.

During planning, expected RSSI is derived from transmit power, antenna gains, cable losses and free-space path loss. If the value measured after installation is well below the calculation, check for misalignment, Fresnel zone obstruction, cable or connector faults, or wrong polarisation. Cellular systems such as LTE and 5G use RSRP and RSRQ for a similar purpose.