Mobile operators are entering the high precision positioning game with Vodafone among the leaders. The operator is partnering with Samcordia, a specialist German company in the field that has just enhanced its own satellite-rooted navigation system.
Accurate positioning down to the decimeter (dm) level, or even to a few centimeters, is vital for a number of prospective 5G applications, including autonomous driving, precision farming, unattended automated vehicle (UAV) operation, and remote drone flying. Accuracy of current navigation systems based on LTE, or for that matter GPS, typically down to a few meters, is inadequate for use cases where errors greater than 1dm can be fatal.
Drones can be flown remotely through use of onboard cameras and sensors, either in autonomous operation or by human pilots viewing images. However the latter only works at relatively short range when latency is reasonably low, while the former is too computationally intensive for many drones.
Furthermore, there are drone applications where precise positioning at a more global level is required. This includes autonomous flying where the path is set by the remote satellite tracking system, or operations where precise altitudes need to be maintained, as well as return-to-home navigation, where a drone returns automatically to its take-off location when summoned. Such applications cannot be served solely by on-board tracking, however accurate.
Then in the case of precision farming, drones may need to be directed accurately to positions in a field for monitoring or sample collection, while in the case of self-driving such remote tracking could help keep in lane in the absence of discernible road markings. There are many other examples that have generated growing interest from providers of mobile technology, as well as operators. Apart from precision, a key requirement is robustness in the field so that accuracy is not lost when a device is unable to pick up a mobile signal, through being out of range or blocked by obstacles such as hills. Equally, there may be cases where accuracy needs to be retained as far as possible in the absence of satellite access.
Another requirement is reasonably rapid convergence, that being the timing process of locking into satellite signals. Because of their distance, there is a variable time lag between transmission and receipt of signals, with receiving devices having to synchronize with these before accurate tracking can proceed. This can be done by the device generating an internal pseudo random number and waiting for that to be exactly in sync with a similar sequence sent by the satellite. The device then knows exactly how long a satellite signal of its position has taken to arrive and can adjust accordingly.
Real Time Kinematics (RTK) has been widely employed to improve positional accuracy of GNSS (Global Navigation Satellite System) tracking, to get down to dms or even cms from a few meters. GNSS here is the generic term for satellite navigation systems in general, although it is sometimes misleadingly confused with the US GPS (Global Positioning System) associated with many of the worldwide tracking and mapping applications in transportation and recreation. GNSS embraces GPS but also the EU’s Galileo, China’s Beidou, Russia’s GLONASS, and some other smaller regional systems.
RTK works by comparing the phases of a given signal received directly from the satellite and re-broadcast from a fixed base station. This allows the location accuracy to be enhanced through comparison with that station whose location is known with high precision. In this way, a drone say can determine its position down to a cm or two, and relative to a nearby drone even more accurately, to mms. RTK then can be used for impressive demonstrations of synchronized drone flying, along the lines of fly pasts at airshows or major public events.
But there is a caveat. RTK requires a connection to a base station, which cannot be guaranteed at all times. Sapcorda came up with a GNSS augmentation service designed to fill in those gaps and achieve more ubiquitous high precision tracking in safety critical applications. Launched December 2020 in the US and Europe, this uses frequencies in the L-band designated for satellite and mobile positioning. All of the GNSS systems transmit their signals in the L-band at different frequencies, which were chosen because they have reasonable penetration through water and light vegetation so that data can usually be received accurately through clouds, rain and light foliage.
Precise Point Positioning (PPP) was then developed to augment RTK by requiring just a single GNSS satellite clock coupled with orbit corrections generated from a network of global reference stations. Crucially, the receiver does not need a direct connection to any of these ground stations. Instead, when corrections have been calculated, they are delivered to the device via satellite, or possibly over some other Internet correction.
Again, this brings accuracy down to the dm level, or potentially somewhat better. One disadvantage however is that PPP takes some time to converge. Sapcorda has reduced that through a hybrid PPP-RTK system that works with two geostationary satellites. In normal operation when mobile Internet connectivity is available, it operates more like a traditional RTK system. But it then swaps to the second satellite feed when Internet connectivity drops out, without interrupting service or reducing accuracy.
“To use GNSS in mass market safety-critical applications, manufacturers need GNSS augmentation services that provide correction data with safety-critical positioning,” said Botho zu Eulenburg, CEO of Sapcorda.
“By expanding our SAPA services with industry-leading L-band transmission, we enable a high-power correction data stream for homogeneous performance and end-to-end data security with continental coverage in the United States and Europe – thus improving accuracy, reducing convergence time, and enabling the use of lower-cost receivers and antennas,” he said.
The Sapcorda L-band signal is transmitted in the open SPARTN format, developed specifically for IP-based and geostationary satellite distributions. It is aimed at safety-critical applications in automotive, working with V2X 5G connectivity for autonomous driving, as well as maritime and various industrial use cases, robotics and drones.
This attracted Vodafone while under development and is now being offered to its enterprise customers. The operator claims to have tested it extensively for cargo and vehicle tracking, reaching that dm level of accuracy.