Why RSSI Is Not Enough for LTE Troubleshooting

When an IoT device has connection problems, the first value most people check is RSSI.
Unfortunately, RSSI is the least useful measurement for LTE networks and often leads to wrong conclusions.

Many installations are declared “network problems” or “modem problems” even though the real issue is signal quality, not signal strength.

This article explains what actually matters.

What RSSI Really Means

RSSI (Received Signal Strength Indicator) measures total radio energy at the antenna.

Important detail:

RSSI does not measure the quality of the LTE signal.
It measures everything the antenna receives.

This includes:

• the LTE cell you want
• neighboring cells
• reflections from buildings
• electrical noise
• interference from other radios

So RSSI answers only one question:

“How much radio energy exists at this location?”

It does NOT answer:

“Can the modem reliably communicate with the network?”

This is why devices often show a “good signal” but still disconnect.

The Measurements That Actually Matter

For LTE IoT (LTE‑M, NB‑IoT, Cat‑1, Cat‑4), three different values determine connectivity reliability:

1) RSRP — Signal Strength of the Serving Cell

RSRP (Reference Signal Received Power) measures the strength of the specific LTE cell your modem is connected to.

Typical ranges:

• >-90 dBm → very good
• -90 to -105 dBm → usable
• -105 to -115 dBm → unstable
• <-115 dBm → likely disconnects

This is the real “coverage” indicator.

2) RSRQ — Signal Quality (VERY IMPORTANT)

RSRQ (Reference Signal Received Quality) is the most overlooked LTE metric.

RSRQ shows how clean the radio channel is.

Typical ranges:

• -3 to -9 → excellent
• -9 to -12 → acceptable
• -12 to -15 → unstable
• <-15 → frequent drops

Here is the surprising truth:

Most IoT failures are caused by bad RSRQ, not weak RSRP.

This commonly happens in:

• basements
• metal cabinets
• near large machines
• inside electrical installations

3) SINR — Noise and Interference

SINR (Signal‑to‑Interference‑and‑Noise Ratio) tells how well the modem can distinguish the LTE signal from noise.

Typical interpretation:

• >20 dB → excellent
• 13–20 dB → good
• 0–13 dB → unstable data
• <0 dB → connection drops

A modem can have strong RSRP but still fail if SINR is poor.

Why RSSI Misleads Installers

Inside buildings, especially near metal surfaces, radio waves reflect.
The antenna receives multiple delayed copies of the same signal.

Result:

RSSI looks strong
but the modem cannot decode the data.

This is extremely common for smart meters, trackers, and industrial sensors.

A classic situation:

• RSSI: good
• RSRP: acceptable
• RSRQ: very bad
• Device disconnects after idle

This is not a carrier issue and not a modem firmware issue.
It is an RF environment problem.

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