Abstract-Increasing numbers of mobile computing devices, user-portable, or embedded in vehicles, cargo containers, or the physical space, need to be aware of their location in order to provide a wide range of commercial services. Most often, mobile devices obtain their own location with the help of Global Navigation Satellite Systems (GNSS), integrating, for example, a Global Positioning System (GPS) receiver. Nonetheless, an adversary can compromise location-aware applications by attacking the GNSS-based positioning: It can forge navigation messages and mislead the receiver into calculating a fake location. In this paper, we analyze this vulnerability and propose and evaluate the effectiveness of countermeasures. First, we consider replay attacks, which can be effective even in the presence of future cryptographic GNSS protection mechanisms. Then, we propose and analyze methods that allow GNSS receivers to detect the reception of signals generated by an adversary, and then reject fake locations calculated because of the attack. We consider three diverse defense mechanisms, all based on knowledge, in particular, own location, time, and Doppler shift, receivers can obtain prior to the onset of an attack. We find that inertial mechanisms that estimate location can be defeated relatively easy. This is equally true for the mechanism that relies on clock readings from off-theshelf devices; as a result, highly stable clocks could be needed. On the other hand, our Doppler Shift Test can be effective without any specialized hardware, and it can be applied to existing devices.

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Metaverse platforms are becoming an increasingly popular form of collaboration within virtual worlds. Such platforms provide users with the ability to build virtual worlds that can simulate real-life experiences through different social activities. In the paper, we introduce a novel platform that provides assistive tools for building an educational experience in virtual worlds and overcoming the boundaries caused by pandemic situations. Therefore, the authors developed a high-level software architecture and design for a metaverse platform named VoRtex. VoRtex is primarily designed to support collaborative learning activities with the virtual environment. It is designed to support educational standards and it represents an open-source accessible solution developed using modern technology stack and metaverse concepts. For this study, we conducted a comparative analysis of the implemented VoRtex prototype and some popular virtual world platforms using Mannien’s matrix. Afterwards, based on the comparison, we evaluated the potential of the chosen virtual world platform and the VoRtex platform for online education. After an interactive demonstration of the VoRtex platform, participants were asked to fill out a questionnaire form. The aim was to enable participants to identify the main advantages of online teaching using the VoRtex platform. Finally, the authors analyzed benefits and disadvantages of collaborative learning between the metaverse platform and real-world classroom sessions.

Abstract-An increasing number of mobile applications and services require that devices are aware of their location. Global Navigation Satellite Systems (GNSS) are the predominant enabling technology. But location information provided by commercial GNSS is not secure, unlike what is the usual assumption. There are only few exceptions in the literature that present GNSS vulnerabilities. In this paper, we contribute the first detailed quantitative analysis of attacks against GNSS-based localization. We show how replay attacks against GNSS can have a significant impact: even against cryptographically secured GNSS instantiations, an adversary can manipulate the location and time calculated by victim GNSS receivers. We explain in detail how such attacks can be mounted, measure their impact, and discuss the effectiveness of possible countermeasures.

Abstract-We address the problem of joint optimal rate allocation and scheduling between media source rate and error protection rate in scalable streaming applications over lossy multipath networks. Starting from a distortion representation of the received media information at the client, we propose a novel optimization framework in which we analyze the performance of the most relevant forward error correction and scheduling techniques. We describe both optimal and heuristic algorithms that find solutions to the rate allocation and scheduling problem, and emphasize the main characteristics of the compared techniques. Our results show that efficient unequal error protection schemes improve the quality of the streaming process. At the same time we emphasize the importance of priority scheduling of the information over the best available network paths, which outperforms traditional first-in-first-out models or network flooding mechanisms.Index Terms-Forward error correction, multipath networks, video streaming.

The innovative spreading codes used to modulate the new Galileo signals create new challenges for receiver designers. It is well known in GNSS that longer integration times are needed to obtain a better sensitivity. However, the existence of the new tiered code concept that consists of the presence of a secondary code on top of the primary code to modulate the RF signal puts a limitation on the coherent integration time for pilot channels similarly to the effect of data bit ambiguity in data channels. Within this context, this paper presents a new algorithm for wiping off the secondary code and thereby increase the coherent integration time while requiring a reasonable implementation complexity as compared to other architectures.

Abstract-The vulnerability against interference, spoofing, and jamming of GNSS receivers is considered nowadays a major security concern. This security threat is exacerbated with the existing market availability of GPS jamming and spoofing equipment sold at reasonable prices. If jamming is the main issue faced at present, spoofing, which allows hijacking someone from the expected path, may lead to even worse consequences. Even with the latest security measures that are going to be deployed on the Galileo PRS signals, GNSS receivers are prone to attacks that are relatively easy to implement. In this paper, we identify different countermeasures and security schemes that can be used against spoofing attacks. These countermeasures include some modifications on the GNSS receiver's side, rather than requiring modifications of the whole existing GNSS infrastructure. More specifically, we propose a detection and protection scheme consisting of several statistical tests, based on the computations of moving variances of Doppler offset and C/No estimates, together with a consistency test of the PVT computation. We evaluate the performance of the proposed scheme through simulations and using a measurement setup consisting of a Spirent GSS8000 full constellation simulator whose output is combined with the one from a rooftop GPS antenna before being fed to a receiver frontend. Finally, we compute the probability of detection and false alarm in spoofing detection using the proposed scheme.

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