RSRP, RSRQ, SINR: Understanding and Monitoring the 4G Signal Quality of Your IoT Devices

· 11 min read
11 min read
Eziwan Team
Eziwan Team
IoT Infrastructure

Your IoT gateway shows "connected" on 4G, but your data comes in intermittently, your VPN disconnects every hour, and your field alerts arrive 30 minutes late. The network “works”—but it’s not working properly. The key is understanding LTE signal quality metrics and knowing when to trigger an alert.

The 4 Key Metrics of the LTE Signal​

1. RSRP — Reference Signal Received Power​

RSRP measures the received power of a reference signal on a specific LTE subcarrier. It is the most commonly used measure of signal strength.

Unit: dBm (decibels-milliwatts)
Typical range: -44 dBm (excellent) to -140 dBm (no signal)

RSRPQualityField Impact
> -80 dBmExcellentNo foreseeable issues
-80 to -90 dBmGoodStable connection, optimal data rate
-90 to -100 dBmFairReduced data rate, possible reconnections
-100 to -110 dBmPoorInstability, significant delays
< -110 dBmCriticalFrequent disconnections, data loss

Watch out for this pitfall: an RSRP of -85 dBm doesn't always mean you have a good connection. In a densely populated area with many users on the same antenna, the signal may be strong but the quality may be poor—that's where RSRQ comes in.

2. RSRQ — Reference Signal Received Quality​

The RSRQ measures the signal's signal-to-interference ratio. It takes into account not only the RSRP but also background noise and interference from neighboring cells.

Formula: RSRQ = (N × RSRP) / RSSI
where N = number of subcarriers, RSSI = total received power

Unit: dB (decibels)
Typical range: -3 dB (excellent) to -19.5 dB (critical)

RSRQQualityRecommendation
> -9 dBExcellent—
-9 to -12 dBGoodMonitor
-12 to -15 dBFairAlert, check antenna
< -15 dBPoorAction required

Real-world example: an industrial site in a suburban area with RSRP = -82 dBm (good) and RSRQ = -16 dB (critical). This site uses an antenna that becomes overloaded during peak hours—its VPNs disconnect between 12:00 PM and 2:00 PM every day. The solution: switch to the secondary carrier (SIM2) during these time periods.

3. SINR — Signal-to-Interference-plus-Noise Ratio​

The SINR measures the signal-to-interference-plus-noise ratio. It is the most accurate indicator of demodulation quality.

Unit: dB
Typical range: > 20 dB (excellent) to < -6 dB (out of service)

SINRModulation SchemeTheoretical Data Rate
> 20 dB64-QAMMaximum (Cat. 4: 150 Mbps DL)
10–20 dB16-QAM60–100 Mbps DL
0–10 dBQPSK10–30 Mbps DL
< 0 dBBPSK< 5 Mbps, unstable

For IoT applications (telemetry, SCADA monitoring, lightweight VPN), a data rate of 1–5 Mbps is sufficient. The critical SINR is around -3 dB—below that, expect frequent retransmissions, which increase latency.

4. RSSI — Received Signal Strength Indicator​

RSSI is the total received power across the entire channel, including all subcarriers. It includes noise and interference. It is less accurate than RSRP for assessing quality, but useful for initial screening.

Unit: dBm
Typical range: -50 dBm to -120 dBm

Common Pitfalls in Industrial Environments​

The Faraday Cage Trap​

Metal electrical cabinets, steel-frame buildings, and shielded rooms create Faraday cage effects. An RSRP of -105 dBm measured from inside a cabinet can become -75 dBm with an external antenna located 2 meters away.

Rule of thumb: In an industrial environment, always use an external magnetic or stand-mounted antenna located outside the cabinet.

The Gradual Deterioration of the Antenna Cable​

A 3-meter RG-174 coaxial cable (the thin cable often included with modems) attenuates the signal by 3 to 5 dBm at 800 MHz. In LTE B20 (800 MHz, used for extended rural coverage), this represents a difference between -100 and -105 dBm—a drop of one quality category.

Recommendation: Use LMR-200 or H155 cable for lengths greater than 2 m. For lengths greater than 5 m, use LMR-400.

Industrial Interference​

Variable-speed drives, arc welding, electric motors, and battery chargers generate RF harmonics in the LTE bands. If your RSRQ or SINR consistently deteriorates during production, this is likely due to local interference.

Diagnosis: Compare the SINR during off-peak hours (night) versus peak hours. If the difference exceeds 10 dB, identify the source of the interference.

Configuring Alerts in Eziwan​

alertes_signal:
  rsrp:
    warning: -100  # dBm — surveiller
    critical: -107  # dBm — basculer SIM
  rsrq:
    warning: -13   # dB — surveiller
    critical: -16   # dB — basculer SIM
  sinr:
    warning: 3     # dB — surveiller
    critical: -1   # dB — basculer SIM

Intelligent Failover Policy​

The Eziwan platform continuously monitors the metrics for both SIM cards. A switchover is triggered if two of the three criteria are in the critical zone at the same time:

Si (RSRP_SIM1 < -107) ET (RSRQ_SIM1 < -16)
   → Basculer vers SIM2
   → Notify the maintenance team
   → Log the event with metrics
   → Switch back to SIM1 if RSRP_SIM1 is greater than -100 for 5 minutes

The "for 5 minutes" criterion prevents the signal from oscillating (ping-ponging) between the two SIM cards when the signal is weak.

Signal Monitoring Dashboard​

On the Eziwan platform, each Gateway has a historical graph of its metrics:

  • RSRP over 24 hours / 7 days / 30 days
  • RSRQ over the same time periods
  • Number of SIM handoffs
  • Signal/VPN latency correlation

This data makes it possible to identify:

  • Gradual deterioration (antenna disconnecting, aging cable)
  • Recurring issues (peak hours, production)
  • One-time incidents (carrier outage, network maintenance)

Best Practices for Industrial IoT Deployments​

1. Always measure before installing​

Before permanently installing your Gateway, measure the signal strength from several locations. In a dense industrial environment, the signal strength can vary from -85 to -95 dBm over a distance of 50 cm.

2. Document the nominal signal​

During installation, record the baseline metrics in Eziwan:

  • Nominal RSRP for SIM1 / SIM2
  • Nominal RSRQ
  • Baseline VPN latency

These values will serve as a baseline for detecting future deterioration.

3. Test failover under real-world conditions​

Simulate a SIM1 outage and verify:

  • Actual failover time (target: < 8 seconds)
  • Continuity of VPN sessions
  • Receipt of failover alerts
  • Automatic return to SIM1

4. Check the coverage of both carriers​

Don't just pick two carriers at random. Use carrier coverage maps and, most importantly, conduct a field test with both SIM cards at the location. Different carriers can have widely varying performance depending on the frequency band and the density of local cell towers.

Case Study: Troubleshooting a Problematic Site​

Situation: Pumping station in a rural area; telemetry data is missing for 3 to 4 hours per day.

Measurements taken:

SIM1 (Orange) — RSRP: -104 dBm, RSRQ: -14 dB, SINR: 2 dB
SIM2 (SFR)    — RSRP: -88 dBm,  RSRQ: -10 dB, SINR: 12 dB
Active failover: 0 times in 30 days

Diagnosis: SIM1 is configured as the primary SIM with failover thresholds that are too lenient (-110 dBm). The site is operating at the signal limit on SIM1, even though SIM2 would be significantly better.

Solution:

  1. Reverse the priority order (SIM2 as primary)
  2. Lower the RSRP failover threshold to -98 dBm
  3. Move the external antenna 40 cm (resulting in a change from -104 to -96 dBm on SIM1)

Result: 0 missing data points over the next 30 days.

Choosing the Right LTE Band for Your Industrial Deployments​

LTE uses different frequency bands, each with its own characteristics. In France, the main bands are:

LTE BandFrequencyCarrierStrengthsLimitations
Band 20 (B20)800 MHzOrange, SFR, BouyguesMaximum rural coverage, excellent building penetrationLimited data rate (max 20 MHz bandwidth)
Band 28 (B28)700 MHzBouygues (deployment)Similar to B20, good coverageLess widely available
Band 3 (B3)1800 MHzAllGood balance of speed and coverageAverage building penetration
Band 1 (B1)2100 MHzOrange, SFRHigh speeds in dense areasLow penetration, limited range
Band 7 (B7)2600 MHzOrange, SFR, BouyguesVery high data speeds (4G+)Very short range, no building penetration

For industrial IoT: Band 20 (800 MHz) is the standard in industrial environments. Its long-range propagation and penetration through metal buildings (attenuation ~5 dB vs. ~15 dB for Band 7) make it the best choice for electrical cabinets and rural sites.

Forcing the LTE band on the Eziwan Gateway:

AT+QCFG="band",F,80000,0      # Force Band 20 uniquement
AT+QCFG="band",F,840000,0    # Force Band 20 + Band 3
AT+QCFG="band",F,0,0          # Auto (toutes bandes)

Forcing Band 20 at a rural site where the RSRP for Band 20 is -95 dBm but the RSRP for Band 3 is -102 dBm can eliminate instability caused by automatic band hopping.

LTE Antenna Selection Guide for Industry​

The antenna is often the overlooked component of an industrial LTE installation. A poor choice or improper cabling can result in a loss of 10 to 20 dBm in gain—the difference between a stable connection and one at the edge of coverage.

Types of Antennas and Use Cases​

TypeGainMountingRecommended Use
Magnetic omnidirectional2–5 dBiCabinet roofStandard sites, good signal, quick installation
Omnidirectional with stand5–7 dBiMast or wall mountSites with average signal, direct line of sight desired
Directional panel (patch)9–14 dBiPointed toward BTS antennaRural sites at the edge of coverage, known direction
Yagi14–20 dBiMast, precise orientationVery remote sites, long-distance connection >5 km
Indoor (on enclosure)0–2 dBiIntegratedOutside metal cabinet, excellent signal

Coaxial Cables: Attenuation as a Function of Length​

The cable between the antenna and the gateway introduces a loss in dBm that adds to the attenuation caused by the medium. Choose based on the required cable length:

Cable TypeAttenuation at 800 MHzRecommended Maximum Length
RG-174 (standard thin cable)1.8 dB/m<1 m (extension cable only)
RG-580.7 dB/m<3 m
LMR-200 / H1550.35 dB/m<8 m
LMR-400 / H5000.15 dB/m<20 m

Rule of thumb: For every meter of RG-174, you lose 1.8 dBm. A 5-meter length of RG-174 cable results in a loss of 9 dBm—which can cause the RSRP to drop from -95 to -104 dBm, a decrease of two quality categories.

Monitoring signal metrics is not a luxury—it is the foundation of a reliable industrial IoT infrastructure. The Eziwan platform continuously collects this data and makes it available for proactive rather than reactive analysis.

FAQ​

What is the difference between RSRP and RSSI? Which one should you monitor first? RSSI (Received Signal Strength Indicator) is the total received power, including all interference—less accurate. RSRP (Reference Signal Received Power) measures only LTE reference signals, filtering out interference—more representative of the actual quality of the LTE signal. In industrial environments with numerous sources of RF interference, RSRP is by far the best indicator. Monitor RSRP first, then RSRQ for channel quality.

My gateway shows an RSRP of -85 dBm—is that sufficient for industrial monitoring? Yes. -85 dBm is an excellent LTE signal. Here is a practical reference scale: > -90 dBm = excellent (no issues), -90 to -100 dBm = acceptable (minor risks), -100 to -107 dBm = degraded (consider an external antenna), < -107 dBm = critical (action required). For an industrial monitoring site using VPN and MQTT, an RSRP > -100 dBm is generally sufficient.

Is the gateway's internal antenna sufficient, or is an external antenna always required? The internal antenna is sufficient if the gateway is housed in a non-metallic enclosure with a clear line of sight. In a metal electrical cabinet (Faraday cage), an external antenna is virtually mandatory—the enclosure attenuates the signal by 10 to 20 dB. Invest in a magnetic or screw-on external antenna for all cabinet deployments.

Further Reading​

Need a signal audit for your existing IoT sites? Contact our technical team.

Additional Resources​