What is RSSI?

Detailed explanation

RSSI represents the total power received by the device across the entire measurement bandwidth. Unlike RSRP which isolates the reference signal, RSSI includes every power source within the channel: the serving cell signal, neighbouring cell interference, thermal noise and any other in-band emissions. This makes RSSI a broadband indicator of the overall radio environment.

In legacy 2G and 3G networks, RSSI was the primary signal strength indicator. In 4G LTE and 5G NR, RSRP has taken over as the preferred coverage metric because it provides a bandwidth-independent measurement of the reference signal. However, RSSI remains essential as it feeds into the RSRQ formula: RSRQ = N x RSRP / RSSI.

The RSSI value depends on the channel bandwidth: wider bandwidth means more noise and interference collected, resulting in higher RSSI values. For this reason, comparing RSSI values between different bandwidths is not meaningful without normalization. A 20 MHz channel will show roughly 3 dB higher RSSI than a 10 MHz channel in similar conditions.

In the field, a high RSSI combined with low RSRP indicates a high-interference environment where most of the received power comes from unwanted sources. This scenario results in poor RSRQ and reduced throughput. Conversely, when RSSI is close to the expected RSRP contribution, the environment is clean with minimal interference.