GPS and GNSS Modules
Unlock global positioning capabilities for your mobile robots. GPS and GNSS modules provide essential coordinate data, enabling seamless outdoor navigation and large-scale fleet tracking beyond the confines of indoor infrastructure.
Core Concepts
GNSS vs. GPS
While GPS is the US-owned system, GNSS (Global Navigation Satellite System) encompasses all satellite constellations including Galileo (EU), GLONASS (Russia), and BeiDou (China) for superior coverage.
RTK Accuracy
Real-Time Kinematic (RTK) positioning uses a fixed base station and a rover module to correct signal errors, improving positioning accuracy from meters down to centimeters for precision tasks.
Triangulation
Receivers calculate position by measuring the time-of-flight of signals from at least four satellites. This trilateration determines 3D position (latitude, longitude, altitude) and precise time.
NMEA Protocols
The National Marine Electronics Association (NMEA) standard is the universal data format for GPS modules. Robots parse NMEA strings (like $GPGGA) to extract location data.
Dead Reckoning
When satellite signals are blocked (tunnels, indoor transition), modules use Untethered Dead Reckoning (UDR) by combining IMU data to estimate position until the signal is restored.
Update Rate
For fast-moving AGVs, the update rate (measured in Hz) is critical. Standard modules update at 1Hz, while robotics-grade GNSS modules often operate at 10Hz to 20Hz for smoother control loops.
How It Works
Global Navigation Satellite Systems (GNSS) function by a network of satellites broadcasting precise time signals. A receiver on the AGV picks up these signals and calculates the distance to each satellite based on the time delay (Time of Flight). By intersecting these distances from at least four satellites, the receiver determines its exact position on Earth.
In robotics, standard GPS accuracy (2-5 meters) is often insufficient for navigation paths. Therefore, modern systems employ Sensor Fusion . The GNSS data provides absolute global position (preventing drift), while local sensors like Odometry and IMUs provide immediate relative movement data.
Advanced implementations use Dual-Band receivers (L1/L5 frequencies) to mitigate multipath interference in urban environments, ensuring the robot maintains a lock even near tall buildings or under tree cover where single-band signals might bounce or degrade.
Real-World Applications
Agriculture Automation
Autonomous tractors and harvesters rely on RTK-GNSS to follow crop lines with sub-inch accuracy, minimizing overlap, reducing fuel consumption, and maximizing crop yield without human intervention.
Last-Mile Delivery Robots
Sidewalk delivery rovers use GNSS for general waypoint navigation between pickup and drop-off points, switching to cameras and LiDAR for local obstacle avoidance on pavements.
Mining & Construction
In open-pit mines, autonomous haul trucks utilize robust GNSS systems to navigate vast, changing terrains where there are no road markings or physical infrastructure to follow.
Inter-Logistics Transport
AGVs operating in large industrial campuses use GNSS to transition between buildings (outdoor mode) and SLAM/Line following (indoor mode) for seamless material transfer.
Frequently Asked Questions
What is the difference between Single-Band and Dual-Band GNSS?
Single-band receivers track satellites on one frequency (usually L1), making them susceptible to interference and signal reflection in cities. Dual-band receivers (L1 + L5) track two frequencies, allowing them to correct for ionospheric errors and reject multipath signals, significantly improving accuracy in difficult environments.
Can GNSS modules work indoors?
Generally, no. Satellite signals are too weak to penetrate concrete and steel roofs effectively. For indoor navigation, robots must switch to LiDAR, visual SLAM, or magnetic tape, although some "high sensitivity" modules can get a rough fix near windows.
What is the "Urban Canyon" effect?
This occurs in cities with tall buildings where the sky view is limited. Satellite signals bounce off buildings before reaching the receiver (multipath error), causing the robot to think it is in a different location. Dual-band GNSS and heavy IMU fusion help mitigate this.
How much power does a GNSS module consume?
Standard GNSS modules are quite efficient, typically consuming between 30mA to 100mA at 3.3V. However, active antennas and RTK processing can increase power draw, though it remains a negligible part of an AGV's total power budget compared to motors.
Why do I need an active antenna?
Passive antennas rely solely on the signal strength from space, which is very weak. Active antennas include a Low Noise Amplifier (LNA) powered by the module to boost the signal before it travels down the cable, which is essential for maintaining signal integrity on robots.
What is Time-To-First-Fix (TTFF)?
TTFF measures how long it takes for a module to determine its position after power-up. A "Cold Start" (no previous data) can take 30+ seconds, while a "Hot Start" (saved almanac data) takes only 1-2 seconds. Battery backup is crucial for fast hot starts.
Is RTK expensive to implement?
Historically yes, but costs have dropped dramatically. You now need an RTK-capable rover module and access to correction data (via NTRIP over 4G or a local LoRa base station). The hardware is now affordable for mid-range commercial robots.
What is Dilution of Precision (DOP)?
DOP is a numeric value representing the geometry of the satellites. If all visible satellites are clumped in one part of the sky, DOP is high (bad accuracy). If they are spread out, DOP is low (good accuracy). Robots should filter data based on DOP thresholds.
How do I interface a GNSS module with a microcontroller?
Most modules use UART (Serial) communication. You connect TX/RX pins and parse the ASCII NMEA data stream. High-end modules might offer USB, I2C, or CAN bus interfaces for faster data rates or easier integration with industrial PCs.
Can magnetic fields affect GPS?
Magnetic fields do not affect the GPS radio signals themselves, but they disrupt the electronic compass (magnetometer) often built into GNSS modules to determine heading. Keep modules away from high-current motors and power lines.
What happens if the GPS signal is jammed?
Jamming causes a loss of position fix. Robust autonomous systems use "Fail-Safe" modes. If GNSS variance spikes or satellites drop to zero, the robot should switch to visual odometry, stop safely, or rely on IMU dead-reckoning for a short period.
What is the standard baud rate for GPS modules?
The default is typically 9600 bps. However, for 10Hz update rates required by robotics, this is too slow. It is standard practice to configure the module to 38400 bps or 115200 bps during the initialization sequence.