The pervasive deployment of Internet of Things (IoT) devices is considered a fundamental brick in the transition towards the Smart City. Small, interconnected, battery-less transceivers, capable of harvesting energy from Radio Frequency (RF) communications are envisioned as a green solution to realize this transition. In this paper, we investigate the possibility of setting up an urban monitoring application through battery-less IoT sensors deployed alongside a road and capable of scavenging energy from mobile wireless sources like traveling vehicles. The proposed Energy Harvesting (EH) model has been derived from experimental measurements, and combined with a vehicular traffic simulator in order to obtain a realistic input power pattern, which takes into account the variable speed and the trajectory of the vehicles. On top of this, a low-energy wireless communication protocol, inspired by the Long Range (LoRa) stack, has been developed, which prescribes periodic data transmission to a remote Access Point (AP). Extensive simulations have been carried out to highlight the impact of several parameters, including storage capacity, load current, data rate, packet size, RF sources intensity and mobility, on the overall system throughput. The obtained results confirm the feasibility of the approach; furthermore, they show that while the peculiar nature of the energy source would make it advantageous to send small packets at higher pace, the opposite strategy (larger packets at lower pace) becomes preferable when the overhead cost is taken into account.

In this paper, we investigate the potential of exploiting Free Space Optical (FSO) transmissions over short links to relay data from vehicular communications to a dedicated Access Point (AP). In the envisioned scenario, a small device capable of Energy Harvesting ($\mathbf{E H}$) from radio frequency signals is placed alongside the road. Using the Simultaneous Wireless Information and Power Transfer (SWIPT) principle, the device obtains both data and energy from passing vehicles. The scavenged energy is then used to power a small optical transmitter and relay the received data to the AP. We address the problem of finding the optimal fraction of incoming energy to be reserved for $\mathbf{E H}$, taking into account the stochastic losses over the optical link. A theoretical expression is derived, and a suitable approximation for some parameters setup is shown. The results, obtained through extensive Monte Carlo simulations, confirm the validity of the analysis, and show how the optimal harvesting range depends on the vehicular traffic characteristics as well as on the implemented schemes for transmissions collision avoidance.

The problem of data privacy preservation is of central importance in ride-sharing applications, because in order to efficiently match passengers with vehicles, these services rely on exact location information. Yet, transportation and location data can reveal personal habits, preferences and behaviors, and users may prefer not to share their exact location. Masking location data in order to avoid the identification of users in case of data leakage, and/or misusage would help protect user privacy, but could also lead to poorer system performance, in terms of efficiency and quality of service as perceived by users.In this paper, we compare classic data masking techniques, namely obfuscation, k-anonymity, and l-diversity, applied to users’ location data, before sending it to a carpooling system. While the first two techniques use randomly generated points to mask the actual location, l-diversity uses actual points of interest, having the additional benefit of ensuring that the disclosed location is always an accessible and safe pickup or drop-off location. Given that users in a real ride-sharing system could choose to protect or not protect their location data when using the system, we also evaluate the effect of privacy preservation penetration rate, by varying the percentage of users choosing to have their location data protected. The results show that l-diversity performance is better than the others’ even when the privacy penetration rate is high, suggesting that this technique has the potential to meet both users’ and system’s needs, and thus being a better option to provide privacy within carpooling systems.

Trip matching algorithms used in ride-sharing and carpooling systems share the common goal of optimizing the number of used vehicles to satisfy a set of trips according to their temporal and spatial constraints, in order to better allocate resources and reduce traffic and congestion. However, each matching algorithm could be designed to pursue a different objective like, for instance, reducing users' waiting time for quality of service, reducing the total amount of traveled distance within the system to reduce carbon footprint, or maximizing the time two trips are shared to favor user interaction. Changing the final system objective could significantly change the performance of the system itself. In this paper, we compare the performance of matching algorithms with different objectives and show whether potential tradeoffs exist in pursuing these objectives, taking into consideration all the actors in play in a mobility sharing application. In particular, by applying the matching algorithms to two sets of daily trips performed in the cities of Pisa, Italy, and Cambridge, USA, our analysis shows that there is a matching algorithm among the ones we tested able to provide a good compromise between different optimization objectives.

Periodic exchange of situational information (beacons) is at the basis of most active safety applications in vehicular environments, and understanding its performance in real-world situations is very important. However, existing studies are focused on measuring the packet delivery rate (PDR), while disregarding the packet inter-reception (PIR) time which has recently been shown to be more relevant than PDR to characterize active safety application performance. In this paper, we fill this gap by presenting an extensive study of the PIR times observed in real-world highway scenarios. We start by showing that PIR cannot be reliably estimated from PDR, since the two metrics are only weakly correlated. Motivated by this finding, we present a thorough characterization of the PIR time distribution, which is shown to be a power law in a variety of configurations. The shape of the PIR time distribution indicates that potentially dangerous “situational awareness” blackouts are relatively frequent and positively time correlated. We then evaluate the effect of vehicle configuration and line-of-sight conditions on the PIR time, and show that relatively simple multi-hop beaconing techniques can substantially improve PIR statistics and, hence, safety. A final contribution of this paper is promoting the Gilbert–Elliot model, previously proposed to model bit-error bursts in packet switched networks, as a very accurate model of beacon reception behavior observed in real-world scenarios.

In this paper, we examine the problem of packet scheduling in a single-hop multichannel system, with the goal of minimizing the average message waiting time. Such an objective function represents the delay incurred by the users before receiving the desired data. We show that the problem of finding a schedule with minimum message waiting time is NP-complete, by means of polynomial time reduction of the time table design problem to our problem. We present also several heuristics that result in outcomes very close to the optimal ones. We compare these heuristics by means of extensive simulations.

Active safety applications for vehicular networks aims at improving safety conditions on the road by raising the level of “situation awareness” onboard vehicles. Situation awareness is achieved through exchange of beacons reporting positional and kinematic data. Two important performance parameters influence the level of situation awareness available to the active safety application: the beacon (packet) delivery rate (PDR), and the packet inter-reception (PIR) time. While measurement-based evaluations of the former metric recently appeared in the literature, the latter metric has not been studied so far. In this paper, for the first time, we estimate the PIR time and its correlation with PDR and other environmental parameters through an extensive measurement campaign based on IEEE 802.11p technology. Our study discloses several interesting insights on PIR times that can be expected in a real-world scenarios, which should be carefully considered by the active safety application designers. A major insight is that the packet inter reception time distribution is a power-law and that long situation awareness black-outs are likely to occur in batch, implying that situation awareness can be severely impaired even when the average beacon delivery rate is relatively high. Furthermore, our analysis shows that PIR and PDR are only loosely (negatively) correlated, and that the PIR time is almost independent of speed and distance between vehicles. A third major contribution of this paper is promoting the Gilbert-Elliot model, previously proposed to model bit error bursts in packet switched networks, as a very accurate model of beacon reception behavior observed in real-world data.

This paper studies, for the first time to our best knowledge, VoIP performance over V2V IEEE 802.11p links. VoIP performance is evaluated in terms of both throughput and jitter through on-the-road measurements, investigating also the effects of inter-vehicle distance and speed on VoIP performance. Results of our study show that VoIP performance is quite poor, especially due to an excessively large number of lost packets under all investigated scenarios. In-lab experiments performed to investigate possible causes of this poor performance reveal that throughput degradation is likely to be due to inefficiencies in implementation of the vehicular networking stack, rather than to poor communication quality.

In this paper, we present a measurement study of application layer performance in IEEE 802.11p vehicular net works. More specifically, our focus is on active safety applications, which are based on the exchange of beacon messages containing status information between close-by vehicles. We consider two performance metrics relevant to active safety applications: the first is application-layer goodput, which can be used to optimize congestion control techniques aimed at limiting the beaconing load on the wireless channel; the second is the beacon reception rate, which is useful to estimate the level of situation awareness achievable onboard vehicles. Our measurements were conducted using a prototypal, 802.11p compliant communication device developed by NEC, in both stationary and mobile V2V scenarios, and disclosed several useful insights on 802.11p application-level performance. To the best of our knowledge, the ones presented in this paper are the first application-level measurements of IEEE 802.11p based vehicular networks reported in the literature.

Radio Frequency IDentification (RFID) systems are becoming more and more popular in the field of ubiquitous computing, in particular for objects identification. An RFID system is composed by one or more readers and a number of tags. One of the main issues in an RFID network is the fast and reliable identification of all tags in the reader range. The reader issues some queries, and tags properly answer. Then, the reader must identify the tags from such answers. This is crucial for most applications. Since the transmission medium is shared, the typical problem to be faced is a MAC-like one, i.e. to avoid or limit the number of tags transmission collisions. We propose a protocol which, under some assumptions about transmission techniques, achieves a 60% performance on the average (in terms of transmitted bits). It is based on a proper recursive splitting of the concurrent tags sets and on signal storing and later cancellation, until all tags have been identified.

In this paper, we approach the problem of identifying a set of objects in an RFID network. We propose a modified version of slotted aloha protocol to reduce the number of transmission collisions. All tags select a slot to transmit their ID by generating a random number. If there is a collision in a slot, the reader broadcasts the next identification request only to tags which collided in that slot. Simulation results show that our approach performs better than framed slotted aloha and query tree based protocols, in terms of number of slots needed to identify all tags, which is a commonly used metric, strictly related to delay

Third generation mobile communication systems will provide more advanced types of interactive and distribution services, and video is one of the most prominent applications for multimedia communications. Adapting the media content to different networks characteristics (communication links and access terminals), in order to enable video delivery with acceptable service quality, is one of the most important problems in this setting. In this paper, we consider one of the video adaptation methods, namely video transcoding, and we present new buffer-based strategies for temporal video transcoding in a real-time context. Simulation results show that our strategies achieve a good performance in hard transcoding conditions also.

LEO/MEO constellations of communication satellites have recently been proposed as a powerful tool for improving internet performance and for extending it beyond the earth (InterPlanetary Internet). Several aspects of such usage must still be investigated. Among them, proper routing and MAC protocols play a prominent role. In this paper,we assume that the MAC protocol is an MF/TDMA one (as usual in satellite communication), and we consider the problem of assigning packets to a set of shortest paths in a satellite constellation, with the goal of minimizing the overall packet scheduling problem. We present an optimal polynomial time algorithm which works offline and balances the load over all possible shortest paths, allowing a minimum schedule length for the entire constellation to be found in polynomial time.