Indoor Bluetooth presence systems often fail for a very simple reason. Someone takes an RSSI number, treats it like a tape measure, and then builds room logic on top of that mistake. That is where trouble starts.

RSSI is useful. We use it all the time in Bluetooth presence work. But RSSI is not distance in the literal, dependable, wall-proof sense many teams want it to be. It is a radio-strength hint, shaped by packet timing, antenna behavior, body blocking, reflections, channel conditions, and plain old indoor messiness. Bluetooth itself still broadcasts legacy advertising on up to three primary advertising channels, and those events are intentionally perturbed in time to reduce collisions. That helps the protocol, but it also means the receiver is not observing one clean, stable signal from one clean direction. ⁽¹⁾⁽²⁾

For Lansitec deployments, this matters a lot because B-Mobile and B-Fixed are powerful systems precisely when they are used for what RSSI does well: presence, proximity, room-level inference, and rough positioning. Lansitec’s own guidance is refreshingly honest here. In B-Mobile, a gateway can often hear a beacon in the next room, but the signal is usually much weaker, and the RSSI gap between the “correct room” and the adjacent room can be up to 20 dBm. The same guidance also says single-point positioning is suitable for room-level and rough tracking, not exact indoor coordinates.

What RSSI Means in BLE Indoor Positioning

RSSI tells you how much signal power arrived at the receiver for a given packet. It does pas tell you, by itself, the real physical path the signal took, whether the packet was partially body-shadowed, whether it arrived after bouncing off metal shelving, or whether the sample came from channel 37, 38, or 39 under slightly different RF conditions. Texas Instruments notes that, in BLE, only the RSSI of the last received packet is reported, with no averaging across channels, and that correlating RSSI directly to distance is not easy because antenna design and polarization affect it heavily. TI also cites expected RSSI accuracy around ±4 dBm in the referenced implementation. ⁽²⁾

That ±4 dBm point may sound small. Indoors, it isn’t.

When Lansitec says an adjacent-room difference can be up to 20 dBm, that sounds comfortable. But “up to” is doing a lot of work there. In clean cases, yes, the right room should look clearly stronger. In borderline cases, especially with open doors, glass, corridors, thin partitions, forklifts, people, and metal cabinets, that margin shrinks fast.

So the right mental model is this: RSSI is evidence of nearness, not proof of exact distance.

Common RSSI Mistakes in Indoor Positioning Systems

We’ve seen three recurring mistakes.

First, teams use a single threshold like “stronger than -70 dBm means inside the room.” Clean on paper. Fragile in a real building.

Second, they ignore timing. In B-Fixed, Lansitec states the tracker’s Réception Bluetooth window is three seconds, and the beacon transmission interval should not be longer than one second, with 800 ms, 500 ms, or less recommended. It even notes that, with a 100 ms interval, the tracker can receive multiple samples in a 3-second window, drop the highest and lowest RSSI, and average the rest. That is not a cosmetic detail. It is exactly how you make RSSI less noisy.

Third, they expect one radio technology to do two jobs. Presence detection is one job. Fine-grained positioning is another. Silicon Labs’ current Bluetooth Channel Sounding guidance is blunt on this point: existing Bluetooth location solutions often rely on RSSI and/or AoA/AoD, but Channel Sounding uses time- and phase-based methods and is expected to be significantly more accurate than RSSI-based measurements. ⁽³⁾

In other words, don’t ask coarse RSSI presence logic to behave like precision ranging.

How to Use RSSI Correctly in BLE Presence Detection

This is where Lansitec’s portfolio is actually quite well segmented.

Dans B-Mobile, fixed Passerelles Bluetooth listen for mobile balises on people or assets. Lansitec recommends an 800 ms advertising interval for fast-walking people, notes indoor transmission distance is typically around 10 to 30 meters, and explicitly warns that next-room reception is common but weaker. Presence detection here is best understood as: the person is near this gateway or in this zone, not the person is exactly 4.2 meters from the east wall.

Dans B-Fixé, the architecture flips. Fixed balises are installed in known places and mobile traqueurs listen for them. Here again, Lansitec describes single-point presence detection as rough tracking and gives the familiar log-distance formula for RSSI-based estimation. Useful? Yes. Absolute truth? No. The same document also explains why shorter advertising intervals improve stability: more packets arrive inside the receive window, so the system can reject outliers and average the rest.

That means a good Lansitec deployment should interpret RSSI in layers:

1. Detection layer: did the device appear at all?
2. Comparison layer: which gateway or beacon saw the strongest and most consistent signal over a short time window?
3. Decision layer: is the evidence strong enough to call room presence, or only corridor/zone proximity?

That third step is where many systems cheat… and where users lose trust.

Best Practices for Using RSSI in Indoor Tracking

Here is the practical rule we’d use in a Lansitec presence deployment: Never decide room presence from one packet. Decide it from a short window of packets plus a margin against the runner-up receiver.

For example:

• Require repeated detections inside a rolling 3- to 10-second window.
• Compare the top receiver to the second-best receiver.
• Use hysteresis so devices do not “ping-pong” between adjacent rooms.
• Treat weak, inconsistent, or near-tied readings as “near boundary,” not “in room 204.”

That logic matches the spirit of Lansitec’s own deployment guidance. B-Mobile says one gateway can work for a relatively small room, but corridor and lobby placement is more economical when the real question is whether someone left the room, not precisely where they are inside it. It also says putting a gateway in every room improves accuracy. That’s exactly right. More certainty usually comes from geometry and placement, not from squeezing one more decimal place out of RSSI.

Why Beacon Placement Matters More Than RSSI Thresholds

If your building has many small rooms and you truly need room confirmation, a gateway-per-room design is often the clean answer. If your goal is to know whether someone has left a room or entered a corridor, fewer passerelles in corridors and lobbies may be enough, and cheaper. Lansitec says as much in its B-Mobile deployment Q&A.

For industrial areas, workshops, or hazardous spaces, Lansitec guidance recommends denser deployment, often around every ten meters, depending on site conditions. Again, that is a geometry decision, more than a software trick.

This is also why product choice matters:

• Passerelle Bluetooth intérieure makes sense where powered indoor coverage is available and room or zone visibility is the goal.
• Passerelle Bluetooth compacte fits temporary or pop-up presence work, but you still need to respect indoor radio ambiguity.
• Passerelle Bluetooth macro is better when you need long-life indoor deployment without mains power.
• Passerelle de proximité macro et Passerelle de proximité SocketSync are especially interesting because they make the right philosophical move: they use RSSI thresholds as configurable proximity triggers, not as claims of exact distance. Lansitec lists a default alarm threshold of -65 dBm, adjustable by the user. That is exactly how RSSI should be used in safety and access workflows: as a trigger signal, not a ruler.

How to Interpret BLE Presence Data Correctly

A mature system does not always say “inside room A.”

Sometimes it should say:

• “detected near room A”
• “likely in room A”
• “between corridor gateway and room gateway”
• “presence confirmed, exact room uncertain”

That may sound less bold, but it is much more credible. And credibility is what keeps operations teams from turning alerts off after two frustrating weeks.

When RSSI Works and When You Need More Accurate Positioning

RSSI is enough when your question is:

• Is the person or asset near this checkpoint?
• Did it enter or leave this zone?
• Which room-level receiver is most consistently strongest?
• Has it stayed near a restricted doorway long enough to trigger a workflow?

RSSI is not enough when your question is:

• How many meters away is it, exactly?
• Which side of the wall is it on, every time?
• Which shelf, bay, or exact workstation is it closest to?
• Can I unlock a door or raise a safety alarm based on a single distance estimate?

The Bluetooth SIG’s current positioning guidance reflects this nicely. It says Bluetooth Channel Sounding can be combined with RSSI, with RSSI handling presence, proximity, and coarse ranging at longer distances and Channel Sounding increasing accuracy as devices get closer. ⁽⁴⁾

That is a smart architecture, and honestly, it matches what experienced deployers have learned the hard way.

How to Improve BLE Indoor Positioning Accuracy

If you are building on Lansitec B-Mobile or B-Fixed, treat RSSI as a decision input, not a distance output.

Use it to rank receivers. Use it to infer room presence when the margin is clear. Use windows, averaging, and hysteresis. Use denser placement when the operational question is stricter. Use configurable proximity passerelles when the outcome is an alert, not a map coordinate. And when the job truly needs sub-meter or decimeter confidence, stop forcing RSSI to do precision work and move to Lansitec AoA or UWB. Lansitec’s own positioning portfolio exists for exactly that reason.

RSSI is not distance. But interpreted properly, it is still incredibly valuable.

Références et lectures complémentaires :

1. Bluetooth SIG: The Bluetooth Low Energy Primer
2. Texas Instruments: RTLS Toolbox – BLE5-Stack User’s Guide
3. Silicon Labs: Bluetooth LE Channel Sounding Fundamentals
4. Bluetooth SIG: Bluetooth Channel Sounding