When an IoT gateway has 4G connectivity issues — frequent disconnections, packet loss, high latency — the first step is to read the LTE signal metrics exposed by the cellular module. These four metrics — RSSI, RSRP, RSRQ and SINR — measure different aspects of connection quality and together allow you to diagnose the root cause precisely. This guide explains what each one measures, what values are acceptable in the field and what to do when they are out of range.
Where to see the metrics on the Index AMI
In the Android app: Overview → Device Status tab → Signal Strength section. The four values update automatically every 20 seconds. They are also accessible via the management platform if the Index AMI is connected via MQTT or TCP.
The four LTE signal metrics
RSSI — Received Signal Strength Indicator
RSSI is the total received signal power, in dBm. It includes both the useful operator signal and background noise and interference. It is the best-known metric but the least accurate for LTE: two gateways with the same RSSI can have very different connection quality if one is in a noisy zone and the other is not.
| Value | Quality | Field IoT interpretation |
|---|---|---|
≥ −70 dBm | Excellent | Strong signal, no issues expected. Typical indoors near antenna. |
−70 to −85 dBm | Good | Stable connection. Most field installations operate here. |
−85 to −100 dBm | Fair | Functional connection but retransmissions possible. Monitor. |
< −100 dBm | Weak | Disconnections likely. Relocate antenna or use external antenna. |
RSRP — Reference Signal Received Power
RSRP measures exclusively the power of LTE reference signals, ignoring noise and interference. It is the main metric for evaluating 4G coverage — more reliable than RSSI because it is not affected by cell load or adjacent signals.
| Value | Quality | Field IoT interpretation |
|---|---|---|
≥ −80 dBm | Excellent | Optimal coverage. Index AMI can operate at maximum data rate. |
−80 to −100 dBm | Good | Adequate coverage for IoT telemetry. Typical field value. |
−100 to −110 dBm | Fair | LTE module reduces data rate. Higher latencies. |
< −110 dBm | Weak | Frequent handover between cells. May cause reconnections. |
< −120 dBm | Critical | No effective coverage. Index AMI may disconnect from operator. |
RSRQ — Reference Signal Received Quality
RSRQ combines signal power with quality: it is the ratio between RSRP and total received power. A low RSRQ (more negative) indicates heavy interference or a heavily loaded cell, even if RSRP is acceptable. Especially useful in dense urban areas with many neighbouring cells.
| Value | Quality | Field IoT interpretation |
|---|---|---|
≥ −10 dB | Excellent | No significant interference. |
−10 to −15 dB | Good | Moderate interference, tolerable for IoT. |
−15 to −20 dB | Fair | High interference. Throughput degrades. Check antenna position. |
< −20 dB | Weak | Highly interfered zone. Consider directional antenna. |
SINR — Signal-to-Interference-plus-Noise Ratio
SINR is the ratio between useful signal power and the sum of interference plus noise. It is the most direct measure of communication quality. A high SINR means the Index AMI can decode data with high reliability. The Index AMI LTE module calculates SINR as raw/2 − 23.5 dB.
| Value | Quality | Field IoT interpretation |
|---|---|---|
≥ 20 dB | Excellent | Maximum channel capacity. Maximum throughput available. |
13 to 20 dB | Good | High reliability. Suitable for real-time telemetry. |
0 to 13 dB | Acceptable | LTE module uses more conservative modulations. Functional for IoT. |
< 0 dB | Problematic | High error rates. Check for interference sources near the Index AMI. |
Which metric to prioritise for diagnosis?
- Use RSRP as the primary coverage reference — it is the most stable and comparable across operators.
- If RSRP is acceptable but there are connectivity issues, check RSRQ — there may be interference from neighbouring cells.
- If RSRQ is good but there are data errors, check SINR — there may be local radio frequency interference (motors, inverters, VFDs).
- RSSI is only useful as a quick reference — do not use it as the sole diagnostic criterion for LTE.
Practical rule: RSRP ≥ −100 dBm and RSRQ ≥ −15 dB is the minimum acceptable for stable IoT telemetry. If both are in range and there are issues, the root cause is usually configuration (APN, keepalive) or local interference.
Scenario-based diagnosis
Scenario 1: Periodic disconnections every few minutes
The Index AMI connects, sends data and then disconnects. The cycle repeats.
- Check RSRP: if between −100 and −110 dBm, the cell has marginal coverage and the module frequently hands over.
- Check the Keepalive configured on the Index AMI (WireGuard and/or MQTT). If less than 25 s, 4G NAT may close the session before keepalive renews it.
- Verify PersistentKeepalive = 25 s on the WireGuard peer.
- If the problem persists, check if scheduled restart is enabled — the Index AMI may be restarting according to the configured period.
Scenario 2: Good signal but high latencies or packet loss
RSRP and RSSI are acceptable, but pings have high jitter or retransmissions are visible in logs.
- Check RSRQ and SINR — if RSRQ < −15 dB or SINR < 5 dB with acceptable RSRP, there is local interference.
- Identify RF sources near the Index AMI: solar inverters, VFDs, motors, transformers. These generate harmonics in cellular bands.
- Try moving the antenna 30–50 cm perpendicular to the interference source.
- If the Index AMI uses an internal antenna and is inside a metal cabinet, switch to an external antenna with cable.
Scenario 3: No LTE connection (module not registered with operator)
The IP Address field in Overview is empty. The operator does not appear in Cell Details.
- Check the APN in Connectivity Configuration — an incorrect APN prevents data network registration.
- Check RSRP: if below −120 dBm or absent, the module has no coverage. Change location or use a directional outdoor antenna.
- Verify the SIM is activated and has an active data plan. Call the operator if necessary.
- Confirm the LTE band in Cell Details — some operators migrate between bands (B2, B4, B28). If the module doesn't support the operator's band in that area, there will be no coverage.
Signal improvement actions
- External antenna: The most effective change. A 5 dBi external antenna improves RSRP by 10–15 dB on average. Use low-loss cable (LMR-200 type) of maximum 3 metres to avoid losing the gain.
- Antenna position: The antenna should have line of sight to the cell tower. Avoid placing it inside metal cabinets — metal attenuates 15–30 dB. Mount the antenna outside the panel if possible.
- Band selection: If the operator offers multiple bands, band 28 (700 MHz) has greater building penetration and range in open field than high bands (2600 MHz). Check which bands your operator offers in the area.
- Operator change: If RSRP is critically low with your current operator, check coverage from other operators at the same site. A different SIM can have 15–20 dB more signal at the same location.
Expected normal values in the field
For typical IoT telemetry installations, the following ranges are the reference:
- RSRP: −85 to −105 dBm — normal operating range for meters in industrial panels.
- RSRQ: −10 to −16 dB — tolerable even in industrial areas with some interference.
- SINR: 5 to 15 dB — sufficient for efficient LTE modulations.
- Latency (ping): 30 to 150 ms over LTE CAT-1 is normal. Spikes of 300 ms are acceptable on mobile networks.
Next steps
With signal in range, verify the APN is correct and Keepalive is properly configured. If connectivity is stable but the meter doesn't respond, the issue is in the RS485 bus — see the RS485 diagnostics guide.