Inside Unmanned Systems

APR-MAY 2017

Inside Unmanned Systems provides actionable business intelligence to decision-makers and influencers operating within the global UAS community. Features include analysis of key technologies, policy/regulatory developments and new product design.

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46 unmanned systems inside   April/May 2017 AIR RESEARCH SUMMARY As the unmanned community works out what drones should broadcast about themselves to meet security needs, there is an opportunity to consider other changes. Including raw data among ADS-B message types from airborne vehicles could greatly reduce collision risk. by Inside Unmanned Systems B roadcasting the raw data enabling ADS-B to generate position—data al- ready existing in GPS receivers—could greatly improve collision avoidance and boost overall system reliability, according to naviga- tion signal expert James L. Farrell of VIGIL, Inc. In a technical paper soon to be published in Inside GNSS magazine and on the websites of Inside Unmanned Systems and Inside GNSS, Farrell describes how using the raw measure- ments already being used by the receiver to develop the aircraft's position could make f light path predictions vastly more accurate. Using raw measurements, for example pseu- doranges, makes it possible to tightly esti- mate velocity and therefore determine more precisely whether aircraft will pass danger- ously close to one another. This approach could also make the overall system more robust. In those cases where there are too few satellites in sight to make a position determi- nation, ADS-B has nothing to broadcast. The raw data is still available, however, and f light path tracking can be ac- complished, if less thorough- ly, with this partial data set. Starting with the raw ingredi- ents instead of the final prod- uct could also make it possible to combine data from a vari- ety of sources for improved, or even entirely new, products. Using Raw GPS Data to Improve Collision Avoidance Differential GPS (DGPS), Farrell reminds us, owes its spectacular success to beginning with raw measurements and building on what that enables—for example, a dramatic improvement in integrity monitoring. This approach is f light validated, uses estab- lished algorithms, readily available universal access transceivers (UATs) and existing com- munication message formats, he writes. The key difference is including the raw pseudo- range and carrier phase data in ADS-B Out messages either in place of, or in addition to, the derived position coordinates. That is not to say this proposal is without chal- lenges. ADS-B Out standards are already set for manned aircraft and it remains necessary to find a way to avoid overloading the ADS-B sys- tem with unmanned aircraft. Moreover, even though it might be possible to tweak current ADS-B transceivers with a software update, those changes would still need to be developed. Even so, it was only a few years ago that ADS-B was widely considered too expensive for unmanned aircraft—then Google found a way to bring the costs down. The Federal Aviation Administration has just begun weigh- ing new rules to meet national security needs, rules that may incorporate ADS-B. This paper proposes—in time for inclusion in the discus- sion—an advantageous and potentially life- saving change in ADS-B messages. The paper will appear in Inside GNSS maga- zine and will be posted on Insidegnss.com and insideunmannedsystems.com. A GPS IIF satellite. Adding raw data available in GPS receivers to drone ADS-B Out broadcasts from dones sharply improves collision avoidance. Photo courtesy of Boeing

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