Satellite-based positioning - A look at future technologies
What is satellite-based positioning actually about? And what benefits does this offer specifically for logistics?
GPS, the Global Positioning System, is the basis for tracking & tracing vehicles and shipments. New systems like Galileo offer several promising possibilities, but even in the future, satellite-based positioning will not be suitable for all applications in logistics.
Where am I? Transporters of goods have been asking this question for more than 2,000 years. Sailors aboard merchant vessels determined their position using landmarks, lighthouses and reliable nautical charts. That was the only way to find the fastest route and estimate the time they would arrive at their destination. The ability to calculate the optimum route and a highly accurate estimated time of arrival (ETA) is still greatly valuable to logistics companies today. To do so, they need to determine the location of all means of transport and shipments—as continuously and as precisely as possible. But nowadays, logistics looks not to landmarks, but to a wide range of wireless beacons.
The best-known of these is positioning by means of a global navigation satellite system (GNSS). For more than 20 years, most of the receivers in vehicles, tracking devices, or smartphones have been processing signals from about 30 US GPS satellites, which orbit the earth at an altitude of 20,000 kilometers. These receivers also make use of positioning data from Russia’s GLONASS or China’s BeiDou system, but only a handful of receivers already use data from the EU’s Galileo satellites. Setup of the Galileo system began in 2011 and is still incomplete; 26 of the planned 30 satellites are in orbit, with the final steps scheduled to finish by 2021–2022. By then, Galileo will be the most advanced GNSS, offering top reliability and the greatest degree of accuracy. But the US continues to gradually upgrade the first and second generations of its GPS satellites, so that in the medium term, all systems will deliver more or less the same data quality.
First- and second-generation GNSS can achieve positioning accuracy of 10 to 15 meters; more sophisticated satellites like Galileo will be able to improve that to 4 to 8 meters. However, several factors can have a negative impact on this precision; signal reflection, for instance, especially in urban canyons. These reflections distort the satellite signal’s exact time of flight, which is necessary for accurately calculating the position. Tests at DACHSER revealed the weaknesses of using GPS to determine, say, which loading gate a semi-trailer is located at. In this use case, GPS alone was unable to achieve 99.9 percent reliability.
One possibility for using GPS to determine a position with greater accuracy (to within 20 centimeters) and reliability is offered by a differential GPS (DGPS). In this system, the transmitter sends an additional signal that is then processed on the ground. The disadvantage of this wireless service is that it is not available everywhere, usually incurs a charge, and causes greater power consumption in the receiver. For these reasons, DGPS is usually a viable solution only in very specific cases. With its High Accuracy Service (HAS), Galileo plans to offer an additional signal directly from orbit to achieve precision to within 20 centimeters. In contrast to the original plans, this service is intended to be free of charge for users. Still, this does not solve the reflection problem, and the HAS will most likely not be able to offer centimeter-level precisions for real-time applications, since processing the additional signal can take up to 30 minutes. At any rate, there have been no practical tests of the HAS because it is not yet available.
Over the next few years, satellite positioning will deliver more precise position data, but for technical reasons, there will still be inaccuracies and restrictions. Inside buildings or in structures such as sea containers, GPS and similar systems will be unable to supply truly precise data even in the future, due to the strong signal shielding. However, logistics players can make use of alternative or complementary “beacons” for positioning, especially cellular base stations, WiFi routers, BLE beacons, RTLS, SLAM, or optical systems—every technology has its own pros and cons. That’s why in the future, there won’t be “one” localization technology for logistics companies. Instead, they will seek out the right mix of technologies for each use case, always searching for the best way to answer the question: “Where am I?”