Various technologies are employed to improve location tracking accuracy in wearables using position/dimension sensors. Combining GPS, IMU, and other sensors effectively is key. Here’s a detailed explanation of each technology and how they are combined:

1. GPS (Global Positioning System):

• Characteristics: GPS calculates the current location by receiving signals from satellites. It offers relatively high accuracy outdoors but suffers from reduced accuracy or signal loss indoors and in areas with dense high-rise buildings. It also has relatively high power consumption.
• Accuracy Enhancement Technologies:
  • A-GPS (Assisted GPS): Uses auxiliary information from cellular base stations or Wi-Fi networks to shorten GPS signal acquisition time and improve initial location fix speed.
  • Dual-Frequency GPS: Employs two or more frequency bands to increase signal accuracy, especially effective in mitigating multipath errors in urban environments.

2. IMU (Inertial Measurement Unit):

• Characteristics: An IMU consists of accelerometers and gyroscopes, measuring the device’s movement and changes in orientation. Unlike GPS, IMUs can track location indoors, but they are prone to accumulating errors over time, known as drift.
• Accuracy Enhancement Technologies:
  • Sensor Fusion: Algorithms like the Kalman filter and complementary filter are used to fuse data from accelerometers and gyroscopes, enabling more accurate motion tracking.
  • Zero Velocity Update (ZUPT): Detects moments when the device’s velocity is zero (e.g., when a foot touches the ground during walking) to correct IMU drift.

3. Other Technologies:

• Wi-Fi Positioning: Estimates location by measuring the strength of surrounding Wi-Fi signals. It can be used indoors to supplement GPS.
• Bluetooth Beacons: Precisely tracks indoor location using strategically placed Bluetooth beacons that transmit signals. Commonly used in shopping malls and museums.
• Barometric Pressure Sensor: Measures changes in atmospheric pressure to estimate altitude changes. Can be used with GPS to improve the accuracy of 3D location information.

4. Combining GPS, IMU, and Other Technologies:

Wearable devices often combine multiple sensors (GPS, IMU, Wi-Fi, barometric pressure sensors, etc.) to maximize location tracking accuracy. This is known as sensor fusion.

• GPS + IMU: When GPS signals are unavailable indoors or weak in certain environments, IMU data is used to estimate location. When GPS signal is regained, it corrects IMU drift, ensuring continuous and accurate tracking both indoors and outdoors.
• GPS + IMU + Barometric Pressure Sensor: Adding altitude information enhances the accuracy of 3D location tracking. For example, it can more accurately track movement during hiking or in high-rise buildings.
• Wi-Fi/Bluetooth + IMU: Indoors, Wi-Fi or Bluetooth beacons can be used instead of GPS to correct IMU drift and provide more precise location tracking.

5. Additional Accuracy Enhancement Techniques:

• Map Matching: Uses map data to correct estimated locations. For example, if a pedestrian is moving along a road, the estimated location can be snapped to the road on the map to improve accuracy.
• Machine Learning: Machine learning models trained on various sensor data and user movement patterns are actively being researched to further enhance location tracking accuracy.

By effectively combining these various technologies, wearable devices are achieving increasingly accurate and reliable location tracking.