Objectives

The transport of goods, the observation of public events, the measurement of buildings, the tasks and the inspection of agriculture – these are only a few of the ways in which mobile systems such as multicopters can be used. If these aerial systems are to be sent out to do their job without human intervention in situations where security and safety are critical, there will always be a need for navigation that is robust, absolutely accurate and proof against interruption or hacking.

This is clear from the example of civilian UAVs (unmanned aerial vehicles). It is only by dint of spot-on, fail-safe navigation that a prescribed route can be followed so exactly that collisions are avoided, flying height kept within limits, no-fly zones avoided, and, in the event of a loss of communication, homing and automatic landing achieved – without any breach of the laws that apply.

Problem

For safety-critical autonomous navigation purposes, commonly and commercially available satnav equipment is out of the question for two reasons: potential breaks or errors in the positioning function, and susceptibility to interference. Satnavs receive their signals from satellites more than 20,000 kilometres away, which means those signals are very weak on arrival and that they are susceptible to the deliberate interference known as GNSS-jamming from transmitters able to send signals perhaps more than a hundred times their strength. Hijacking of the flying object itself is also a possibility.

Solution (step 1): a compact four-channel GNSS receiver

For these reasons it fell to the German Aerospace Centre (DLR), the Ilmenau University of Technology, the RWTH Aachen and IMMS to research new designs, technology and algorithms for the sort of more compact adaptive group antennas necessary to eliminate satnav signal disruption. These are capable of fulfilling very high interference-mitigation specifications, but those developed so far were too large and heavy for actual mobile use. A receiving unit was designed by IMMS and partners which was only a quarter of the size of a conventional group antenna but had the same number of individual elements. It has proved the applicability of the signal treatment techniques. IMMS’ part was to develop the receiver front end circuit forming the link between the antenna array and the digital evaluation software.

Solution (step 2): fail-safe and more compact receiver with 16 channels for increased accuracy and robustness

In the KOSERNA project the same partners have constructed an industrial prototype on the basis of the results achieved in 2013 in conjunction with the antenna engineering company Antennentechnik Bad Blankenburg GmbH. In parallel, the partners have worked on the issues of significantly increased accuracy and robustness for a novel receiver unit. For it, IMMS as subcontractor to Ilmenau TU (Technische Universität) has extended the frontend circuits and transferred the new principles onto a second frequency band. The new prototype was fully tested at the Automotive Galileo Test Environment (GATE) in Aldenhoven, Germany. Good results were obtained in a number of test drives in real situations exposed potentially to disruption with which the standard GPS equipment commercially available would fail to cope.