Reference
Terms & Acronyms
Glossary
| Term | Acronym | Category | Definition | Links |
|---|---|---|---|---|
| Inertial Measurement Unit | IMU | Motion | A sensor package that typically includes a 3‑axis accelerometer and gyroscope, and often a magnetometer. Used to estimate motion and orientation through sensor fusion. | |
| Micro‑Electro‑Mechanical Systems | MEMS | Hardware | Miniaturized mechanical and electro‑mechanical elements fabricated using microfabrication techniques. Most phone motion and pressure sensors are MEMS. | — |
| Accelerometer | - | Motion | Measures specific force including gravity. Linear acceleration is obtained by removing gravity through filtering or fusing with other sensors. | |
| Gyroscope | - | Motion | Measures angular velocity around device axes. Subject to drift; commonly fused with accelerometer and magnetometer for stable orientation. | — |
| Magnetometer | - | Geomagnetic | Measures the local magnetic field vector. Requires calibration and tilt compensation to compute compass heading. | — |
| Barometer | - | Environment | Measures air pressure. Useful for floor‑level changes and weather trends; often combined with temperature for correction. | — |
| Photoplethysmography | PPG | Vitals | Optical technique to detect blood volume changes. With a phone, camera + LED can be used at the fingertip to estimate heart rate. | — |
| Bluetooth Low Energy | BLE | Radio | Low‑power wireless protocol. Beacons advertise identifiers; RSSI can be used for coarse proximity and room‑level presence. | — |
| Received Signal Strength Indicator | RSSI | Radio | A measure of received signal power. Often used to estimate proximity to BLE beacons; highly noisy and environment‑dependent. | — |
| Global Navigation Satellite System | GNSS | Location | Satellite‑based positioning (GPS, GLONASS, Galileo, BeiDou). Provides absolute position mainly outdoors; often fused with IMU for continuity. | — |
| Sensor Fusion | - | Algorithms | Combining multiple sensor signals (e.g., accel + gyro + magnetometer) to estimate states like orientation; common filters include complementary, Kalman, and Madgwick. | — |
| Calibration | - | Best Practices | Procedures to correct sensor biases and scaling errors. Includes hard/soft‑iron correction for magnetometers and bias estimation for gyroscopes. | — |
| Sampling Rate | - | Signal Processing | Number of samples per second (Hz). Motion sensing commonly uses 50–200 Hz; too low misses dynamics, too high increases noise and power use. | — |
| Filtering | - | Signal Processing | Transforms like low‑pass, high‑pass, and band‑pass to shape signals and reject noise. Essential for PPG HR, step detection, and orientation estimation. | — |