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We have recently developed a method that allows the quantification of spare capacity in urban taxi systems through trip sharing (1), hence making it more efficient and less resource intensive—all other things being equal—in particular fares, which can be modified by public policy. In their comment on our study, Lopez et al. observe that a complete evaluation of the environmental sustainability of taxi sharing requires not only considering direct impacts, but also indirect impacts (2). We fully agree with this observation. For limiting the scope of our analysis (1) to a manageable extent, and in lack of an established methodology for quantifying the impacts of vehicle sharing at the granularity of single trips, we were not able to account for effects that can be considered as exogenous to the taxi system. Indeed, urban and regional models are composed of both exogenous and endogenous variables, and “much of the ongoing research agenda can be focused on transferring variables from the exogenous to the endogenous category” (3). The extensions suggested by Lopez et al. (2) and in our report (1) go exactly along this direction.

Multi-hop propagation of situational information is a promising technique for improving beaconing performance and increasing the degree of situational awareness onboard vehicles. However, limitation on beacon size prescribed by standardization bodies implies that only information about 3-4 surrounding vehicles can be piggybacked in a beacon packet. In most traffic situations, the number of vehicles within transmission range is much larger than 3-4, implying that multi-hop forwarding strategies must be devised to select which neighboring vehicle's information to include in a transmitted beacon. In this paper, we investigate the effectiveness of different multi-hop forwarding strategies in delivering fresh situational information to surrounding vehicles. Effectiveness is estimated in terms of both average information age and probability of experiencing a situational-awareness blackout of at least 1 sec. Both metrics are estimated as a function of the hop distance from the transmitting vehicle, and in presence of different level of radio channel congestion. The investigation is based on extensive simulations whose multi-hop communication performance is corroborated by real-world measurements. The results show that network-coding based strategies substantially improve forwarding performance as compared to a randomized strategy, reducing the average information age of up to 60%, the blackout probability of up to two orders of magnitude. We also consider the effect of multi-hop propagation of situational information on the reliability of a forward collision warning application, and show that network-coding based propagation yields a factor three improvement of reliability with respect to a randomized forwarding strategy, and even higher improvements with respect to the case of no propagation.

The burgeoning "sharing economy" phenomenon--the collaborative consumption of shared resources made possible by the pervasiveness of information technologies and Internet connectivity [4, 6]--is rapidly taking hold in the context of urban transportation. Business is booming for vehicle-sharing companies, such as Zipcar and Car2Go, and for companies that offer ride-sharing services, such as Bandwagon and Uber, which recently launched the new UberPool application. New sharing services/companies are popping up in cities worldwide.

The widespread availability of mobile devices along with recent advancements in networking capabilities make opportunistic mobile social networks (MSNs) one of the most promising technologies for next-generation mobile applications. Opportunistic Mobile Social Networks supplies a new perspective of these networks that can help you enhance spontaneous interaction and communication among users that opportunistically encounter each other, without additional infrastructure support. The book explores recent developments in the theoretical, algorithmic, and application-based aspects of opportunistic MSNs. It presents the motivation behind opportunistic MSNs, describes their underpinning and key concepts, and also explores ongoing research. Supplies a systematic study of the constrained information flow problem Reviews the recent literature on social influence in complex social networks Presents a complete overview of the fundamental characteristics of link-level connectivity in opportunistic networks Explains how mobility and dynamic network structure impact the processing capacity of opportunistic MSNs for cloud applications Provides a comprehensive overview of the routing schemes proposed in opportunistic MSNs Taking an in-depth look at multicast protocols, the book explains how to provide pervasive data access to mobile users without the support of cellular or Internet infrastructures. Considering privacy and security issues, it surveys a collection of cutting-edge approaches for minimizing privacy leakage during opportunistic user profile exchange. The book concludes by introducing a framework for mobile peer rating using a multi-dimensional metric scheme based on encounter and location testing. It also explains how to develop a network emulation test bed for validating the efficient operation of opportunistic network applications and protocols in scenarios that involve both node mobility and wireless communication.

In this paper, we tackle the problem of designing a random mobility model generating a target node spatial distribution. More specifically, we solve a long standing open problem by presenting two versions of the well-known random waypoint mobility model in bounded regions generating a uniform steady-state node spatial distribution. In the first version, named temporal-RWP, we exploit the temporal dimension of node mobility and achieve uniformity by continuously changing the speed of a mobile node as a function of its location and of the density function of trajectories in the movement region R. In the second version, named spatial-RWP, we instead exploit the spatial dimension and achieve uniformity by selecting waypoints according to a suitably defined mix of probability density functions. Both proposed models can be easily incorporated in wireless network simulators, and are thus of practical use.The RWP models presented in this paper allow for the first time completely removing the well-known border effect causing possible inaccuracies in mobile net- work simulation, thus completing the picture of a "perfect" simulation methodol- ogy drawn in existing literature.

International audience; In this paper, we tackle the problem of designing a random mobility model generating a target node spatial distribution. More specifically, we solve a long standing open problem by presenting two versions of the well-known random waypoint (RWP) mobility model in bounded regions generating a uniform steady-state node spatial distribution. In the first version, named temporal-RWP, we exploit the temporal dimension of node mobility and achieve uniformity by continuously changing the speed of a mobile node as a function of its location and of the density function of trajectories in the movement region R. In the second version, named spatial-RWP, we instead exploit the spatial dimension and achieve uniformity by selecting waypoints according to a suitably defined mix of probability density functions. Both proposed models can be easily incorporated in wireless network simulators, and are thus of practical use. The RWP models presented in this paper allow for the first time completely removing the well-known border effect causing possible inaccuracies in mobile network simulation, thus completing the picture of a "perfect" simulation methodology drawn in existing literature.

In this paper, we study the feasibility problem in MIMO networks, under the assumption that unilateral inter- ference cancellation is performed. The fundamental problem of MIMO feasiblity refers to whether it is possible to sup- port specified numbers of streams allocated to the links of a MIMO network while cancelling all interference. In unilateral interference cancellation, nodes account only for interfering links that they have been assigned to cancel and ignore other interfering links. This can be safely done because, under a proper interference cancellation assignment, the ignored interference is assigned to other nodes for handling. We present several different formulations of the unilateral feasibility problem and use these formulations to analyze the problem's complexity and develop heuristic feasibility algorithms. We first prove that the general unilateral feasibility problem is NP-complete. We then identify several special cases where the problem is solvable in polynomial time. These include when only receiver-side interference cancella- tion is performed, when all nodes have two antenna elements, and when the maximum degree of the network's interference graph is two. Finally, we present several heuristic feasibility algorithms derived from different problem formulations and we evaluate their accuracies on randomly generated MIMO networks.

Periodic exchange of situational information (beacons) is at the basis of most active safety applications in vehicular environments. Despite its fundamental role in raising the level of "situational awareness" onboard vehicles, very little is known to date on beaconing performance in a real vehicular environment. This paper analyzes the results of two measurement campaigns that have been designed with the purpose of disclosing beaconing performance in a variety of vehicular links, for what concerns vehicle configuration (tall/short), line-of-sight conditions (LOS/NLOS), as well as single-hop or two-hop propagation of the information reported in the beacons. For the first time, beaconing performance is characterized in terms of not only the packet (beacon) delivery rate (PDR), but also in terms of the packet (beacon) inter-reception (PIR) time. The latter metric has been suggested in the literature as more accurately measuring the level of "situation awareness" onboard vehicles than the traditional PDR metric. This paper also presents a simulation-based analysis aimed at estimating the benefit of multi-hop propagation of situational information beyond the second hop of communication. The analysis of the data collected in the measurement campaigns as well as the simulation-based analysis disclose a number of interesting insights which might prove useful in the design of active safety applications. Finally, another 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 scenarios.

In this paper, we study the performance of the beaconing mechanism underlying active safety vehicular applications in presence of different levels of channel congestion. The importance of this study lies in the fact that channel congestion is considered a major factor influencing communication performance in vehicular networks, and that ours is the first investigation of the effects of congestion based on extensive, real-world measurements. The results of our study reveal that congestion has a profound impact on the most important beaconing performance metric, namely, packet (beacon) inter reception time, influencing not only the average value, but also the shape of the distribution. Congestion also considerably increases the frequency of potentially dangerous situation-awareness blackouts, with a likely negative impact on the effectiveness of active safety applications. Our study also reveals that multihop propagation of beaconing information can be used as an effective means of lessening the negative impact of congestion on beaconing performance.

Many mobile social networking applications are based on a ``friend proximity detection" step, according to which two mobile users try to jointly estimate whether they have friends in common, or share similar interests, etc. Performing ``friend proximity detection" in a privacy-preserving way is fundamental to achieve widespread acceptance of mobile social networking applications. However, the need of privacy preservation is often at odds with application-level performance of the mobile social networking application, since only obfuscated information about the other user's profile is available for optimizing performance. In this paper, we study for the first time the fundamental tradeoff between privacy preservation and application-level performance in mobile social networks. More specifically, we consider a mobile social networking application for opportunistic networks called interest-casting. In the interest-casting model, a user wants to deliver a piece of information to other users sharing similar interests (``friends"), possibly through multi-hop forwarding. In this paper, we propose a privacy-preserving friend proximity detection scheme based on a protocol for solving the Yao's ``Millionaire's Problem", and we introduce three interest-casting protocols achieving different tradeoffs between privacy and accuracy of the information forwarding process. The privacy vs. accuracy tradeoff is analyzed both theoretically, and through simulations based on a real-world mobility trace. The results of our study demonstrate for the first time that privacy preservation is at odds with forwarding accuracy, and that the best tradeoff between these two conflicting goals should be identified based on the application-level requirements.

Software Defined Radio testbeds are becoming increasingly used in the wireless networking community, given their feature of leaving wireless network designer full control of the PHY layer. On the other hand, SDR testbeds are formed of very complex software/hardware tools, in which implementation bugs are likely and difficult to identify. For this reason, assessment of the results provided by an SDR platform should be a fundamental, preliminary step in the performance evaluation process. In this paper, we provide a thorough assessment of the MIMONet SDR platform for network-level exploitation of MIMO technology. To assess the platform, we have used two different implementations of an OFDM transceiver: one based on Matlab, the other on the GNU Radio software. We have then crossvalidated performance by means of extensive measurements using the two alternative implementations. We have also designed and implemented a fine grained SNR and BER estimation methodology, that allowed us to carefully validate performance of the two software implementations against theoretical predictions. When collectively considered, the results of our measurements promote MIMONet as the first SDR testbed with carefully validated performance.

Multi-hop propagation of situational information is a promising technique for improving beaconing performance and increasing the degree of situational awareness onboard vehicles. However, limitation on beacon size prescribed by standardization bodies implies that only information about 3-4 surrounding vehicles can be piggybacked in a beacon packet. In most traffic situations, the number of vehicles within transmission range is much larger than 3-4, implying that multi-hop forwarding strategies must be devised to select which neighboring vehicle's information to include in a transmitted beacon. In this paper, we investigate the effectiveness of different multi-hop forwarding strategies in delivering fresh situational information to surrounding vehicles. Effectiveness is estimated in terms of both average information age and probability of experiencing a situational-awareness blackout of at least 1 sec. Both metrics are estimated as a function of the hop distance from the transmitting vehicle. The investigation is based on extensive simulations whose multi-hop communication performance is corroborated by real-world measurements. The results show that network-coding based strategies substantially improve forwarding performance as compared to a randomized strategy, reducing the average information age of up to 60%, the blackout probability of two orders of magnitude, and providing a performance similar to that of an idealized strategy in which complete situational information is included in the beacon.

This chapter contains sections titled: Radio Channel Models The Communication Graph The Energy Model References

This chapter contains sections titled: Real‐World WLAN Traces Features of WLAN Mobility References

This chapter contains sections titled: Wireless Sensor Networks: State of the Art Wireless Sensor Networks: User Scenarios WSNs: Perspectives Further Reading References

This chapter contains sections titled: Active Mobility of Sensor Nodes Active Mobility of Sink Nodes References

Message forwarding is a fundamental brick to spread information among users in opportunistic networks. In this paper, we consider the recently proposed interest-casting networking primitive for opportunistic networks, according to which a packet generated by a sender should be delivered to all users in the network — potentially unknown to the sender — sharing similar interests. However, the current implementation of interest-casting assume users exchange their interest profiles to take forwarding decisions, thus revealing very sensitive information to strangers. In this work, we approach for the first time the problem of designing an interest-casting protocol while not revealing sensitive information during the forwarding and message delivery process. In particular, we present a privacy-preserving mechanism based on the well-known Millionaires' problem allowing users to discover whether they have similar interests without disclosing private information. Based on this mechanism, we propose four different privacy-preserving forwarding protocols to realise interest-casting in opportunistic networks, and we compare their performance on a real-world mobility trace.

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 measurementbased 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.

Mobility Models for Next Generation Wireless Networks: Ad Hoc, Vehicular and Mesh Networksprovides the reader with an overview of mobility modelling, encompassing both theoretical and practical aspects related to the challenging mobility modelling task. It also:Provides up-to-date coverage of mobility models for next generation wireless networksOffers an in-depth discussion of the most representative mobility models for major next generation wireless network application scenarios, including WLAN/mesh networks, vehicular networks, wireless sensor networks, and opportunistic networksDemonstrates the practices for designing effective protocol/applications for next generation wireless networksIncludes case studies showcasing the importance of properly understanding fundamental mobility model properties in wireless network performance evaluation

The tremendous advances in wireless networks, mobile computing, and sensor networks, along with the rapid growth of small, portable and powerful computing devices, offers more and more opportunities for pervasive computing and communications. This topic deals with cutting-edge research in various aspects related to the theory and practice of mobile computing or wireless and mobile networking. These aspects include architectures, algorithms, networks, protocols, modeling and performance issues, data management, and novel applications and services. The aim of this topic is to bring together computer scientists and engineers from both academia and industry working in this exciting and emerging area of pervasive computing and communications, to share their ideas and results with their peers.

In this paper, we address the problem of balancing the network traffic load when the data generated in a wireless sensor network is stored on the sensor node themselves, and accessed through querying a geographic hash table. Existing approaches allow balancing network load by changing the georouting protocol used to forward queries in the geographic hash table. However, this comes at the expense of considerably complicating the routing process, which no longer occurs along (near) straight-line trajectories, but requires computing complex geometric transformations. In this paper, we demonstrate that it is possible to balance network traffic load in a geographic hash table without changing the underlying georouting protocol. Instead of changing the (near) straight-line georouting protocol used to send a query from the node issuing the query (the source) to the node managing the queried key (the destination), we propose to “reverse engineer” the hash function used to store data in the network, implementing a sort of “load-aware” assignment of key ranges to wireless sensor nodes. This innovative methodology is instantiated into two specific approaches: an analytical one, in which the destination density function yielding quasiperfect load balancing is analytically characterized under uniformity assumptions for what concerns location of nodes and query sources; and an iterative, heuristic approach that can be used whenever these uniformity assumptions are not fulfilled. In order to prove practicality of our load balancing methodology, we have performed extensive simulations resembling realistic wireless sensor network deployments showing the effectiveness of the two proposed approaches in considerably improving load balancing and extending network lifetime. Simulation results also show that our proposed technique achieves better load balancing than an existing approach based on modifying georouting.

In this paper, the problem of deriving the power angular scattering response (PASR) resulting from a Gaussian scatterer distribution is undertaken. The scatter cluster can be located arbitrarily in the vicinity of the mobile unit. Furthermore, for the considered scatter geometry we derive both the angular and distance statistics at the observation point, allowing a theoretical characterization of the PASR. A major byproduct of this analysis is that the Gaussian scatterer hypothesis is formally shown to produce a Gaussian power angular spectrum in a macrocell environment, which is in accordance with existing measurements.

In this paper, we present a framework for analyzing routing performance in delay tolerant networks. Differently from previous work, our framework is aimed at characterizing the exact {\em distribution} of relevant performance metrics, which is a substantial improvement over existing studies characterizing either the expected value of the metric, or an asymptotic approximation of the actual distribution. In particular, the considered performance metrics are {\em packet delivery delay}, and {\em communication cost}, expressed as number of copies of a packet circulating in the network at the time of delivery. Our proposed framework is based on a characterization of the routing process as a stochastic coloring process, and can be applied to model performance of most stateless delay tolerant routing protocols such as epidemic, two-hops, spray and wait, etc. After introducing the framework, we present examples of its application to derive the packet delivery delay and communication cost distribution of two such protocols, namely epidemic and two-hops routing. \noindent Characterizing packet delivery delay and communication cost distribution is important to investigate fundamental properties of delay tolerant networks. As an example, we show how packet delivery delay distribution can be used to estimate how epidemic routing performance changes in presence of different degrees of node cooperation within the network. More specifically, we consider fully cooperative, non-cooperative, and probabilistic cooperative scenarios, and derive nearly exact expressions of the packet delivery rate under these scenarios based on our proposed framework. The comparison of the obtained packet delivery rate estimation in the various cooperation scenarios suggests that even a modest level of node cooperation (probabilistic cooperation with a low probability of cooperation) is sufficient to achieve 2--fold performance improvement with respect to the most pessimistic scenario in which all potential forwarders drop packets.

In this paper, the angular power spectrum exhibited under a three-dimensional (3-D) Gaussian scattering distribution at fixed observation points in space is investigated. Typically, these correspond to the mobile and base units, respectively. Unlike other spatial channel models, the derived model accounts for the distance to each scatterer from the observation point, and transforms distances into power values under the assumption of free-space propagation. The proposed 3-D spatial channel model follows a non-central approach in terms of the scatterer distribution in space, which means that the angular power field at the base unit need not be due to a scatterer distribution centered exactly at the mobile. Derivations are provided for the angular and power domains. As shown, by conditioning the distance, the angular field reduces to the von-Mises Fisher distribution. Most importantly, this work provides a theoretical backup to the Gaussian angular power spectrum observed in radio propagation channel measurements, introducing a formal theoretical framework consistent with the experimental investigations found in literature. More specifically, our findings show that a Gaussian scatterer distribution in space gives rise to a Gaussian-like angular power spectrum and a Gaussian angular power density in the azimuth and elevations fields. By introducing the notion of distance into the framework, the proposed 3-D spatial channel model can be used to evaluate performance of current and future multi-element wireless communication networks.

A MIMO network is a wireless network made up of individual MIMO links. The problem we consider is to maximize throughput in a multihop MIMO network with interference suppression. Our problem formulation accounts for variable rates on the MIMO links, which depend on the channel conditions of the link, and the manner in which the diversity-multiplexing trade-off is handled. We present an ILP formulation of the MIMO one-shot scheduling problem with variable rates, which is the first exact formulation of a MIMO network optimization problem that accounts for full interference suppression capabilities of MIMO links. We use CPLEX to evaluate the optimal solution based on the ILP formulation for wireless networks with up to 32 concurrently transmitting links. We also modify a heuristic algorithm from a related MIMO scheduling problem to work in our problem setting. Results show that the heuristic can scale to networks with 80 or more concurrent links, but is 10–20% from optimal in terms of throughput. We show that the heuristic scheduler is not able to fully exploit the diversity-multiplexing-interference suppression tradeoff, which is inherent in the problem. This shows that there is substantial room for developing improved scheduling algorithms for MIMO networks and provides some insight into promising directions to explore.