Septentrio RAIM+ Explained: GNSS Integrity Monitoring
RAIM+ is Septentrio’s receiver autonomous integrity monitoring: a fault-detection layer that runs inside the receiver, tests every measurement for internal consistency, and drops bad ones before they reach the position solution. Where AIM+ suppresses interference, RAIM+ protects the fix from corrupted measurements — high-altitude multipath, ionospheric disturbance, or a single satellite carrying a bias. The outcome is RTK you can still trust when conditions degrade.
Need a receiver with integrity monitoring built in? Tell us your environment and we will recommend the right configuration — Request a quote, or browse rugged receiver boxes and OEM boards.
What RAIM+ Actually Does
RAIM+ spans every level of receiver fault detection: measurement generation, quality control and the navigation algorithms themselves. When an erroneous measurement appears — typically caused by high-altitude multipath or an active ionosphere — it is removed from the solution as soon as it is detected.
This is not a cosmetic filter. A single biased carrier-phase measurement can drag a fixed RTK solution away from the truth while the receiver still reports “fixed”. RAIM+ exists to make that failure mode visible and correctable inside the receiver rather than downstream in your application.
Why a Statistical Approach Beats a Fixed Threshold
Integrity monitoring works by carefully evaluating the statistical character of all observations and error sources. Those characteristics are not constant — they adapt to the dynamics and the environment: vehicle speed, multipath density, atmospheric conditions and signal strength all shift the statistics.
The receiver therefore runs several statistical tests that cross-check the internal consistency of the measurement set. A fixed signal-to-noise threshold cannot do this; it flags a weak but healthy satellite while accepting a strong one carrying a coherent bias. Consistency testing catches the bias instead.
Detection, Alarm, Repair
- Detect — a statistical test fails, so the receiver raises an alarm rather than silently degrading.
- Repair — the receiver attempts to repair the solution by excluding the offending measurement.
- Fall back — if that is not possible, it switches to another positioning mode instead of reporting a false fix.
The decision algorithms behind those steps are coordinated through extensive testing and user experience across many environments, so that the receiver is neither over-sensitive nor complacent. Test strictness can be tuned further with the SetRAIMlevels command to match a specific application’s needs.
Worked Example: A Bias Injected into One Satellite
Consider a static field test with relatively heavy multipath, tracking the RTK fixed height deviation. At epoch 494000 a time-linear bias was deliberately added to the GPS PRN 19 L1 phase measurement.
- RAIM+ disabled — the injected bias produces significant distortion in the height solution; the receiver reports a fixed solution that has moved.
- RAIM+ enabled — the height deviation stays inside the nominal error band, and the effect of the bias is not visible in the output at all.
That is the practical difference integrity monitoring makes: the same corrupted input, a materially different output.
RAIM+ and AIM+ Are Not the Same Job
| RAIM+ | AIM+ | |
|---|---|---|
| Protects against | Corrupted or inconsistent measurements | Radio interference, jamming, spoofing |
| Operates at | Measurement consistency and solution integrity | RF front end (notch filters and wideband mitigation) |
| Typical trigger | Heavy multipath, canopy, ionospheric activity | In-band jammers, nearby transmitters, spoofers |
| Control | SetRAIMlevels strictness | Notch filter and WBI configuration |
Most demanding deployments want both: AIM+ to keep the signal environment usable, RAIM+ to keep the resulting solution honest.
Why It Matters When You Specify a Receiver
Centimetre-level accuracy is only valuable if the fix is genuine. In machine control, port automation, robotics and mapping, an unflagged bad fix is more expensive than a visible loss of lock — it silently corrupts the record, the guidance or the as-built. Integrity monitoring is the part of the specification that protects the rest of it.
If you are comparing receivers, ask what happens at the measurement level when the environment turns hostile — not just what accuracy figure appears on the datasheet.
FAQ
What does RAIM+ stand for?
Receiver Autonomous Integrity Monitoring. The “+” denotes Septentrio’s implementation, which adds multi-level fault detection across measurement generation, quality control and the navigation algorithms.
Does RAIM+ replace AIM+ anti-jamming?
No. AIM+ mitigates radio-frequency interference and spoofing at the front end; RAIM+ evaluates measurement consistency and solution integrity. They address different failure modes and are complementary.
Can I tune how strict RAIM+ is?
Yes — the SetRAIMlevels command adjusts test strictness so integrity monitoring can be matched to the application’s tolerance for false alarms versus missed faults.
What happens when RAIM+ detects a bad measurement?
The receiver raises an alarm, removes the offending measurement from the solution, and if the solution cannot be repaired it switches to another positioning mode rather than reporting a misleading fix.
Where does RAIM+ matter most?
Environments with heavy multipath or active ionospheric conditions, and any application where an unflagged bad fix carries real cost — machine control, robotics, port automation and survey.
Still comparing options? Send us your operating environment and accuracy requirement — request a quote or contact our team, and we will point you at the right receiver configuration.
