RSSI (Received Signal Strength Indicator)

Received Signal Strength Indicator (RSSI) is the power a receiver reports for a radio packet, almost always in dBm. More negative means weaker. A BLE beacon at a few meters on a hall floor often lands around -70 dBm. The same packet at the far end of an aisle can sit near -90 dBm. The number is not a distance. It is a sample the location engine turns into proximity or, with several beacons, a position.

Passive RTLS on an Android tablet lives on those samples. Fixed beacons advertise. The tablet scans. Each callback carries an identifier and an RSSI. The engine needs a stream of those pairs, not one lucky hit, because RSSI jitters with body shadowing, mast steel, and 2.4 GHz Wi-Fi. Starve the scan and you still see unique beacons. You just update them too slowly for a moving truck.

Two tablets in the same room can report almost the same last RSSI and still disagree on how often they hear each beacon. That split, and how to bench it, is in Lenovo TB305XU limits iBeacon scan versus Teclast T50 Mini.

Key Components

dBm reading: Instantaneous received power for one advertising packet. Typical BLE floor values sit between about -40 dBm (close) and -100 dBm (edge of hearability).

Sample rate: How many RSSI values arrive per beacon per second. This is bounded by the BLE advertising interval and by how much scan time the OEM firmware still grants the app.

Filter and average: Location engines smooth RSSI because a single packet can jump several dB. Smoothing needs several packets inside a short window. One sample per second is not the same input as two and a half.

Last RSSI vs capture ratio: A live last-RSSI field can look healthy while the tablet is dropping most advertisements. Score packets versus the advertising interval, not the last dBm line.

Applications in Manufacturing and Logistics

On a forklift tablet, RSSI from a grid of ceiling or column beacons is how zone-level indoor position is computed. The pin on the twin is only as honest as the sample stream. Logistics uses that pin for which hall the truck is in, empty travel, and spaghetti. Safety uses it for no-go entry. People tracking uses the same radio on a phone in a pocket.

RSSI is also the cheap proximity check: a strong reading means the tablet is near that beacon, a weak one means it is not. That is enough for many aisle and zone jobs. It is not a centimeter ranging method. When the job needs a tight cell, the radio choice is a different decision, covered in starting with the decision, not the radio.

Benefits and Challenges

RSSI needs no extra ranging hardware on a consumer Android tablet. That is why plants start BLE RTLS on phones and tablets they already buy. The challenge is that RSSI is noisy and that the tablet must actually deliver the packets. Firmware that throttles BLE scan for battery or memory cuts the sample rate while the UI still says Scanning.

Steel aisles, body blocking, and shared 2.4 GHz spectrum already eat RSSI quality. A throttled scanner adds a second loss that looks like a coverage hole. Bench the device before you blame the beacon grid.

Related Terms

RSSI is the strength sample on BLE and similar radios. How often the beacon emits is the advertising interval. The delay from air to app callback is a form of latency. Positioning that uses these samples is an indoor positioning system / RTLS layer. Metal bounce that confuses strength is multipath.

Frequently Asked Questions

Is RSSI the same as distance? No. Path loss, antenna orientation, and blockers change dBm without a clean meter scale. Engines infer proximity from many samples, not from one reading.

Why can last RSSI look fine while tracking is late? Last RSSI is one packet. Tracking needs a stream. A tablet can hear a beacon at -70 dBm and still deliver only a third of the advertisements the beacon is sending.

What RSSI is too weak to use? There is no universal cutoff. On a hall floor, packets near -95 to -100 dBm are often at the edge. Use them as presence, not as a precise range, and confirm with a scan bench in that pocket.

Does UWB use RSSI the same way? UWB positioning is usually time of flight, not strength. RSSI may still be logged. It is not the primary range.