The Global Positioning System (GPS) accurately calculates a receiver's location on Earth by receiving signals from multiple satellites. Positioning modules, such as the ATGM336H, use a serial port (UART) at a specific baud rate (e.g., 9600) to send positioning information to the main control chip. The transmitted data conforms to the NMEA-0183 standard. Taking the $GNRMC statement as an example, it includes UTC time, positioning status (A valid/V invalid), latitude and direction, longitude and direction, etc. The received raw latitude and longitude data is in degree-minute format and needs to be converted before it can be used for map applications.
Positioning startup is categorized into cold start, warm start, and hot start depending on the conditions. A cold start refers to the process of starting GPS in an unfamiliar environment until the coordinates are calculated, such as when using it for the first time or when ephemeris information is lost; the initial positioning time is approximately 1-2 minutes. A hot start refers to starting the device in a location where it was last turned off without much movement and less than 2 hours after the last positioning; in open sky conditions, positioning can be as short as 2 seconds. Warm start refers to a start that occurs more than two hours after the last positioning, with positioning time falling between cold start and warm start.
Positioning accuracy is affected by various factors. Under open sky conditions, typical horizontal positioning accuracy can reach 3-10 meters. Velocity measurement accuracy is better than 0.1 m/s. Sensitivity determines positioning capability in weak signal environments; for example, acquisition sensitivity can reach -148 dBm, and tracking sensitivity can reach -166 dBm.
Modern positioning technologies often employ multi-mode fusion positioning to improve performance. Multi-mode fusion positioning refers to achieving higher positioning accuracy through multi-mode algorithm fusion calculations using multiple positioning data. For example, it may simultaneously or selectively support multiple Global Navigation Satellite Systems (GNSS) such as GPS, BeiDou (BDS), GLONASS, and Galileo. Furthermore, it is supplemented by cellular network (LBS) and Wi-Fi-assisted positioning. When GPS signal is poor, the system can automatically switch to Cell or Wi-Fi networks for positioning, improving positioning speed, accuracy, and reliability in complex environments.