edVirtus Reference

What Is Received Signal Strength Indicator?

How Does RSSI Estimate the Strength of a Received Wireless Signal?

The Received Signal Strength Indicator (RSSI) is a measurement used by many wireless communication systems to estimate the power of a received radio signal. RSSI provides an indication of how strongly a receiver is detecting a transmitted signal and is widely used in technologies such as Wi-Fi, Bluetooth, Zigbee, LoRa, and cellular communications to assist with network management and link assessment.

The basic principle is straightforward. As a radio signal arrives at a receiver, the receiver measures its strength before or during signal processing. The resulting RSSI value is reported either as a numerical index or, more commonly, as an approximate signal level expressed in decibel-milliwatts (dBm). Because radio signals arriving at a receiver are usually very weak, RSSI values are almost always negative. For example, an RSSI of approximately –30 dBm represents an exceptionally strong signal, –60 dBm indicates a good connection, while values below about –90 dBm generally indicate a weak or unreliable link.

A useful analogy is listening to someone speaking across a room. The louder the voice, the easier it is to hear. However, loudness alone does not guarantee that every word can be understood if there is considerable background noise or several people speaking simultaneously. Likewise, RSSI indicates signal strength but does not account for all factors affecting communication quality.

RSSI is widely used by wireless devices when selecting an access point, roaming between networks, adjusting transmission power, estimating distance, and displaying signal-strength bars to users. Network administrators also use RSSI measurements during wireless site surveys to optimise access point placement and identify areas with inadequate coverage.

One limitation of RSSI is that it is not standardised across all wireless technologies or manufacturers. Different devices may calculate RSSI using different scales or internal algorithms, making direct comparison difficult. Furthermore, RSSI measures only the received signal power and provides no direct indication of interference, background noise, packet errors, or available throughput.

It is important to distinguish RSSI from the Signal-to-Noise Ratio (SNR). RSSI indicates how strong the received signal is, whereas SNR compares the received signal power with the background noise level and is often a better predictor of communication performance. Likewise, RSSI differs from the Received Signal Reference Power (RSRP) used in LTE and 5G cellular systems, which provides a more precisely defined measurement for cellular network planning and optimisation.

Today, RSSI remains one of the most widely reported measurements in wireless communication systems because it is simple to obtain and useful for assessing radio coverage. Although it should not be interpreted as a complete measure of link quality, RSSI continues to play an important role in wireless network operation, device roaming, and troubleshooting across a broad range of modern communication technologies.