The global navigation satellite system (GNSS) has been used to achieve precise positioning of everything from robot lawnmowers to heavy equipment and ride-sharing vehicles but the technology, in spite of offering ubiquitous coverage, suffers from coverage interruptions. Inherent errors due to small inaccuracies in Satellite Clocks and Orbits as well as Ionospheric and tropospheric disturbances can delay the signals. RTK (Real Time Kinematics) correction data from networks of static base stations can correct for these errors and bring the positioning accuracy down to centimetre levels to achieve precise positioning needed for all manner of applications.
Mark Winton, GNSS Product Manager, Quectel Wireless Solutions further explores.
There can be situations where GNSS signals are attenuated by heavy vegetation or obstructed completely inside tunnels or partially by tall buildings in dense urban canyons. This leads to the GNSS receiver receiving the signal via a longer path reflected from a building or experiences cancelation of the signal due to multipath where the signal is received from two or more paths leading to inaccuracy.
These negative effects and obstructions combine to make uninterrupted accurate positioning from GNSS in all scenarios unrealistic.
Many applications are dependent on GNSS being reliable in all situations. A ride sharing vehicle such as an e-scooter, for example, might rely on GNSS to ensure it cannot enter a geofenced area such as a highway or a pedestrian walkway and is not left parked in an inconvenient location. Being unable to provide a precise location hinders this essential performance characteristic and could lead to hefty fines from the city management. Similarly, if a customer is unable to locate the scooter, they can’t start their ride leading to a potential loss of revenue.
Robot lawnmowers are another example which rely on GNSS to set out the area to be mowed, thereby removing the need for guide wires to be installed in gardens. If the system doesn’t know the precise position of the lawnmower, the device cannot ensure it cuts only the grass efficiently in the area specified. Users will not be happy if their mowers that don’t have precise positioning capabilities cut across their prized flowerbeds.
Techniques to preserve precision There are many such examples and use cases including land surveying, construction, agriculture, robotics, and some logistics services that need highly precise positioning that is accurate down to just a few centimetres as well as resilient positioning capability even when experiencing challenging signal environments. Adding Inertial Measurement Unit (IMU) to GNSS receivers allows for dead reckoning to be added to the solution. While the RTK provides higher accuracy in favourable signal environments, the Dead Reckoning (DR) provides increased resiliency in difficult or non existent signal environments.
DR is a process for calculating the position of a moving object by using its previously known position and then estimating the next position based on the object’s speed, direction of travel, and the elapsed time from the last position. When allied to the global positioning system (GPS); DR provides a powerful means to maintain location fixes even when the satellite network is temporarily obscured.
Eliminate the guesswork
RTK correction provides a highly accurate solution that removes the errors out of positioning to provide very accurate measurements. The technology utilises a nearby reference station with known coordinates or a network of reference stations, also known as NetworkRTKs (NTRK) to provide position correction data in real-time via a cellular, broadcast radio or satellite carrier. GNSS computes its position by calculating the distance between a satellite navigation receiver and a satellite from the time it takes for a signal to travel from the satellite to the receiver. RTK improves this measurement by removing the errors in the measurement.
The basic principle behind RTK is that it utilises the carrier-phase differential techniques to compensate for common errors from satellite and atmospheric conditions. This approach significantly improves the GNSS accuracy to the centimetre or decimetre level in open or semi open environments. These compensations can then be accessed by the mobile receiver – such as a delivery robot or autonomous vehicle – which can use these corrections to calculate its own precise position relative to the fixed stations.
This level of location accuracy is an essential foundation for many IoT applications, but RTK correction is complex to enable and requires partnerships with multiple base station owners so data to enable precise positioning calculations can be accessed. The calculations themselves are further complicated by the need to consider services and components from multiple vendors. To mitigate the complexity, IoT organisations are increasingly turning to RTK correction service providers who can handle the calculations and relationships on their behalf, delivering highly accurate device position data.
Make accuracy easy
The process of ensuring centimetre-precise positioning is greatly simplified when delivered by a single vendor that can provide the specialised RTK capable antenna, RTK and DR capable GNSS modules, cellular connectivity and a Global RTK correction service. This approach ensures the complexity can be abstracted away from the IoT organisation while ensuring its’ users benefit from accurate real-time positioning, regardless of the GNSS conditions.
Quectel’s RTK Correction Services, for example, rely on partnerships with multiple best-in class, modern base station owners across five continents to ensure accurate positioning for customers in industries as diverse as precision agriculture and mining to micromobility and telematics. Combined with the 360-degree design review and antenna tuning services Quectel can ensure the path to precision is a smooth one.
By adopting multi-band GNSS, RTK and DR technologies, businesses can achieve unprecedented levels of accuracy and reliability for device positioning. The process has been radically simplified by the emergence of global service providers that offer RTK correction. This has removed the barrier of needing to perform complex calculations and establish partnerships with base station owners worldwide and RTK correction is increasingly widely available.
As the IoT market continues to grow, accurate positioning is playing a pivotal role in unlocking its full potential. Global RTK correction services, allied to DR, are essential capabilities for the rapidly growing marketplace of applications that rely on accurate and robust location to keep users safe, to facilitate easy device discovery and ensure access to precise positioning is democratised.
This article originally appeared in the October 24 magazine issue of IoT Insider.
