Spoofing Detection Performance of Snapshot OSNMA Under Time and Symbol Errors

In the recent years there have been intense research efforts to protect users of Global Navigation Satellite Systems (GNSS) from spoofing attacks that aim to mislead the user's navigation solution by means of counterfeit signals. Galileo, the European GNSS, has been at the forefront of such efforts and implemented already its so-called Open Service Navigation Message Authentication (OSNMA) protocol, intended to authenticate the navigation message and thus provide a protection layer not existing before in any other GNSS open signal. Rather than message authentication, this paper focuses on a novel technique for detecting the presence of potential spoofers by taking advantage of the unpredictability of some of the OSNMA data. Such opportunistic method is based on processing short sequences of received unpredictable symbols, sending them to a remote trusted server where access to the authentic unpredictable symbols is available, and then comparing both the received and the expected sequences for detecting potential mismatches. This approach is well-suited for receivers operating in snapshot mode, which can only gather and process a short piece of received signal due to their limited wireless connectivity, as in many Internet-of-Things (IoT) devices with low-power constraints. Interestingly, the problem addressed herein has some similarities with frame synchronization in digital networks. At the same time, though, it poses new challenges such as the presence of propagation errors, time uncertainty and different propagation times among different satellites, thus deserving a dedicated study.