Vehicular Access Research Articles

Improving EDCA for Efficient Channel Access in Vehicular Communications

With the development of artificial intelligence, IoT, and high-performance computing, modern vehicles are becoming more and more connected and autonomous, which is deeply dependent on wireless communications for information exchange and sharing between the vehicle and the surrounding environment. IEEE 802.11p is a standard protocol designed for low latency and high mobility of vehicular communications. However, the Enhanced Distributed Channel Access (EDCA) of 802.11p with static access category queue allocation and fixed backoff parameter setting cannot meet the requirement of efficient vehicular channel access. In light of this, we improve EDCA by prioritizing messages and adjusting backoff window values dynamically to guarantee the timely delivery of real-time messages. Simulation results show that the proposed mechanism has higher throughput and lower transmission delay for efficient vehicular communications.

Partially buried conveyor belt to allow vehicular access across wildlife fencing

ABSTRACTResearchers and managers often need vehicular access into areas fenced to protect wildlife, but commonly used vehicle crossings often are cumbersome, cost‐prohibitive, or inadequate at restricting target taxa. We describe a cost‐effective method using partially buried conveyor belt, which is flexible and sturdy enough to allow convenient and frequent vehicular passage across wildlife fencing while not compromising the integrity of the barrier or harming the target species. We have no evidence of any target taxa (i.e., tortoises, freshwater turtles, toads) breaching a conveyor belt barrier from projects in central Florida (2005–2012), Guadalupe County, Texas (2014–2018), or Robertson County, Texas (2014). The proposed technique is unlikely to prevent large‐bodied, saltatory, climbing, or arboreal taxa from crossing a wildlife barrier. However, this technique is applicable to many small vertebrates and any taxa for which silt‐fencing or other similar semipermanent barriers are appropriate. © 2018 The Wildlife Society.

Cross-Polarized Three-Dimensional Channel Measurement and Modeling for Small-Cell Street Canyon Scenario

In emerging heterogeneous networks, small-cell base stations deployed along urban streets can increase the network capacity for vehicular access significantly. To fully exploit the potential of full-dimensional multiple-input-multiple-output technologies, it is critical to understand the propagation characteristics of the small-cell vehicle-to-infrastructure (V2I) access channels. In this paper, a measurement campaign for the three-dimensional propagation with $\pm 45^\circ$ polarizations was conducted at 2.6 GHz in a typical urban street canyon environment. We utilized a sounder with two cross-polarized uniformed planar arrays. The transmitter was placed on the rooftop of a five-storey building and the receiver was placed at the 15th position along a street with the line of sight (LOS). The elevation/azimuth of arrival (EoA/AoA), power spectrum, and root-mean-square angular spread of arrival (ESA/ASA) of the multipath components were measured. We propose a dual-Laplace probability density function (PDF) model for the EoA distributions that have LOS clusters and ground reflections. We propose two models, the flat-bottom Laplace PDF and the superposed Laplace PDF, to describe the clustering behavior of the AoA distributions. We also propose the Lognormal models for the ESA and ASA distributions. Furthermore, it is found that polarization does not affect the EoA and AoA distributions, but has a significant impact on the ASA and ESA. The measurement results and channel models can help with the design and evaluation of the spatial transmission/multiplexing technologies in the small-cell V2I access.

Role of infrastructure and other environmental factors affecting the distribution of alien plants in the Tatra Mts

Alien plants, although usually rare in mountain habitats, can significantly impact native species diversity. The aim of this study was to analyse patterns of alien plant distribution in the Tatra Mts (Slovakia), focusing primarily on comparison of various transportation routes as a conduit for the spread of alien plants. We collected data on transects along: (i) railways, (ii) paved roads with unlimited access, (iii) tourist routes in mountain valleys (paved and unpaved roads, footpaths) with limited access and (iv) plots in areas surrounding mountain chalets. The majority of alien plants were found in locations at lower elevations and with intensive human activity. Patterns of distribution along the main corridors in the Tatras reflect the intensity and manner of use of each transportation route. Paved roads with unlimited access and railways are used most frequently and host the greatest number of alien species. Our observations show that the mode of access of these routes is more important than the road surface. Roads with limited vehicular access, be it unpaved and paved, are very similar in their alien species richness, while paved roads with limited and unlimited access significantly differ. Footpaths that cannot be accessed by vehicles are almost free of alien plants, even though they are found in the widest elevation range and often parallel to roads in the same valley. Other factors significantly negatively affiliated with alien species richness were elevation, cover of the tree and moss layer and moisture, and positively affiliated with the amount of nutrients.

Cities Hosting Holy Shrines: The Impact of Pilgrimage on Urban Form

This paper explores pilgrimage in the context of historic holy cities which contain at least one religious complex through which the ritual of pilgrimage takes place. One controversial tension in urban development process of holy cities is the tension between urban growth, on the one hand, and adapting city structure to the needs of pilgrims on the other hand. This paper investigates this issue by referring to experiences of two major holy cities in of Mecca and Mashhad. Both cities are spiritual centers which host millions of pilgrims throughout year. The aim of this paper is to analyze the process of city center transformation in both cities and monitor different policies and interventions that shaped their morphologies up to now. Through historical analysis of urban form, flow of pilgrims has affected the morphology of both cities in similar ways. Accordingly policies and interventions by local officials have shaped the urban center in three similar ways: enlargement and expansion of shrine, vehicular access to shrine, and real-estate speculation. İn the absence of protective and preventive codes and policies both Mecca and Mashhad have lost their historical urban fabric and their cultural patrimonies. Their traditional urban scape and prominence of shrine has been substituted by high rise mega projects. İn a similar way their local crafts and small-scale retails have been replaced by global retail chain.

Vehicular Radio Access to Unlicensed Spectrum

Connection to/among vehicles has been bound to one of the dominant wireless use cases in the upcoming decade. To support the booming applications, scarce bandwidth allocated for vehicle connection has become a performance bottleneck and rigidifies further evolution of future technologies. This concern consequently drives the utilization of unlicensed spectrum with ample bandwidth, on which communications nevertheless should comply with regulatory requirements such as listen-before-talk, which results in unique challenges. For next generation vehicular radio access to unlicensed spectrum, in this article, we develop dual designs to inherit the distinct engineering spirits of 3GPP LTE and IEEE 802.11ax. The proposed LTE-based vehicular radio access should integrate 3GPP vehicle-to-everything connection, licensed assisted access, and device-todevice proximity services to address the particular issues of sidelink shared channel collision and resource uncertainty on uplink, downlink, and sidelink. The proposed IEEE 802.11ax-based vehicular direct radio access emphasizes providing a qualityof-service-guaranteed sidelink access scheme to enable direct vehicle data exchange. The proposed designs pave a foundation to deploy vehicle-to-everything in unlicensed spectrum.

Beach vulnerability assessment of a protected area of the Northern Campania coast (Southern Italy)

A detailed and multidisciplinary study of physical and biotic factors of a coastal sector of southern Italy, the Pineta della foce del Garigliano SCI (Site of Community Importance) area, has been carried out in the frame of the European research project LIFE + Nature & Biodiversity PROVIDUNE. We evaluated the degree of dunes vulnerability (Dune Vulnerability Index, DVI) and sustainable anthropogenic load (carrying capacity) of the emerged beach of the study area, which is largely affected by shoreline retreat and degradation of dune habitat. The values of about 0.6 of the DVI in the two key sectors of the study area suggest a high level of vulnerability of beach/dune system due to both natural and human factors. The partial vulnerability index related to the geomorphological condition exhibits the highest values, as a consequence of a coastal system largely affected by recent and present-day beach erosion and severe hydrodynamics processes. Several inadequate human practises have been recognized in the study area whose impact appears to be an important factor in controlling the reduction of the beach-dune system resilience. Integrated analysis of DVI and carrying capacity suggests that the northern and central sectors of the study area have a high level of dune vulnerability due to hydrodynamic and geomorphological factors whereas the human impact can be considered relatively less important. The southern sector of the study area is featured by a well-developed infrastructure system, which is able to assure a sustainable beach occupation. Nevertheless, significant interventions such as dune replacement by permanent or ephemeral infrastructures, uncontrolled pedestrian or vehicular access and inappropriate use of mechanical beach cleaning have been recognized in this sector of the beach. These long-lasting impacts have promoted the dismantling of large sector of the dune habitats. Obtained results allowed identifying the critical area where appropriate actions can be performed for the mitigation of impacts, the conservation of dune habitats and their sustainable use.

A Feedback Aware Reliable Transport Protocol with Improved Window Increment Mechanism for Inter Vehicular Wireless Network

In recent years, inter vehicular networking technologies are gaining momentum due to its merger with wireless internet through infrastructure gateways. A large quantity of internet data traffic heavily relies on transmission control protocol (TCP) due to reliable connection oriented services. TCP with sluggish window growth and weakly shaped congestion control mechanism fails under multi-hop inter vehicular conditions due to disjoint links and wireless channel errors. This paper introduces inter vehicular access network (IVAN) TCP, designed to suppress the limitations of congestion control and window increment algorithm in the multi-hop inter vehicular wireless environment. The IVAN’s flexible window increment algorithm newer growth pattern achieves a faster increase in the transmission rate. Furthermore, IVAN’s congestion control algorithm reduces the transmission rate based on sender’s window utility and relay router’s explicit congestion notification. The simulation results confirm the significant rise in IVAN’s throughput performance, substantial reduction in the queue packet drop and packet latency against standard TCP variants under inter vehicular environment.

A review of wireless access vehicular environment multichannel operational medium access control protocols: Quality-of-service analysis and other related issues

In recent years, the increase in vehicular traffic has led to a drastic increase in road accidents, thus requiring adequate vehicle safety measures. The intelligent transportation system is a branch of modern technology responsible for delivering such road safety services. The wireless access vehicular environment standard defines how these intelligent transportation system applications can be incorporated in highly varying vehicular ad hoc network environments. Wireless access vehicular environment comprises the IEEE 802.11p and IEEE 1609.4 standards responsible for handling medium access control and transmission mechanisms in vehicular ad hoc networks. However, these standards still face medium access control and physical layer challenges, which must be addressed for reliable quality of service. Several research studies have been proposed and are still underway into improving medium access control protocols in the wireless access vehicular environment stack model defined by IEEE 1609.4 multichannel oper...

$i$CAR-II: Infrastructure-Based Connectivity Aware Routing in Vehicular Networks

With the high demand of mobile Internet services, vehicular ad hoc networks (VANETs) have become a promising technology to enable vehicular Internet access. However, the development of a reliable routing protocol to route data packets between vehicles and infrastructure gateways is still a challenging task due to the high mobility and frequent changes of the network topology. The conventional position-based routing (PBR) in VANETs can neither guarantee the existence of a routing path between the source and the destination prior to the transmission nor provide connection duration information, which makes it unsuitable to route Internet packets. In this paper, we propose a novel infrastructure-based connectivity aware routing protocol called $i$ CAR-II that enables multihop vehicular applications, as well as mobile data offloading and Internet-based services. $i$ CAR-II consists of a number of algorithms triggered and run by vehicles to predict local network connectivity and update location servers with real-time network information, in order to construct a global network topology. By providing real-time connectivity awareness, $i$ CAR-II improves the routing performance in VANETs by dynamically selecting routing paths with guaranteed connectivity and reduced delivery delay. Detailed analysis and simulation-based evaluations of $i$ CAR-II demonstrate the validity of using VANETs for mobile data offloading and the significant improvement of VANETs performance in terms of packet delivery ratio and end to end delay.

A spectrum handoff scheme for optimal network selection in Cognitive Radio vehicular networks: A game theoretic auction theory approach

The recent strides in vehicular networks have emerged as a convergence of multi radio access networks having different user preferences, multiple application requirements and multiple device types. In future Cognitive Radio (CR) vehicular networks deployment, multiple radio access networks may coexist in the overlapping areas having different characteristics in terms of multiple attributes. Hence, it becomes a challenge for CR vehicular node to select the optimal network for the spectrum handoff decision. A game theoretic auction theory approach is interdisciplinary effective approach to select the optimal network for spectrum handoff. The competition between different CR vehicular node and access networks can be formulated as multi-bidder bidding to provide its services to CR vehicular node. The game theory is the branch of applied mathematics which make intelligent decision to select the optimal alternative from predetermined alternatives. Hence, this paper investigates a spectrum handoff scheme for optimal network selection using game theoretic auction theory approach in CR vehicular networks. The paper has also proposed a new cost function based multiple attribute decision making method which outperforms other existing methods. Numerical results revel that the proposed scheme is effective for spectrum handoff for optimal network selection among multiple available networks.

Efficient MAC protocol for drive‐thru Internet in a sparse highway environment

The demands for vehicular Internet access are proliferating. To enable vehicular communications, roadside units (RSUs) can be deployed along the roadside to provide wireless coverage and network access for driving-thru vehicles and the performance of vehicle to RSU communications have been studied in multiple contexts. However, there is not still an efficient media access control (MAC) scheme specific for the sparse highway environment. In this study, the authors investigate the MAC scheme of drive-thru Internet in a sparse highway environment by a Markov chain encountering model. The analytical model incorporates the high-node mobility with the modelling of distributed coordination function (DCF) and unveils the impacts of mobility velocity and number of vehicles on the throughput. On the basis of the model, they develop a new MAC scheme and show that when vehicle number is small the proposed MAC scheme can obtain higher throughput and mitigate the impacts of vehicle mobility on the system throughput, which is desirable for the sparse highway environment. Using extensive simulations, they validate the accuracy of the analytical model and effectiveness of the proposed MAC scheme.

Congestion Control for Vehicular Networks With Safety-Awareness

Vehicular safety applications require reliable and up-to-date knowledge of the local neighborhood. Under IEEE 802.11p, this is attained through single-hop broadcasts of safety beacons in the control channel. However, high transmission power and node mobility can cause regions of node density to form rapidly. In such situations, excessive load on the control channel must be avoided to prevent performance degradation for safety applications. Existing congestion control schemes aim to reach a fair distribution of available channel resources, but fail to account for the differing quality of service (QoS) requirements of vehicles in different driving contexts. This context depends on many factors, including the relative position and velocity of its neighbors. The problem of adapting each vehicle's transmission probability under a slotted p-persistent vehicular broadcast medium access control (MAC) protocol is formulated as a network utility maximization (NUM) problem which takes the driving context into account. A distributed algorithm is proposed to solve this problem in a decentralized manner, its convergence is analyzed, and its performance is evaluated through simulations.

Toward Multi-Radio Vehicular Data Piping for Dynamic DSRC/TVWS Spectrum Sharing

Enabling high-throughput and cost-effective vehicular communications is important for many emerging vehicular applications, such as safety applications, traffic management, and mobile Internet access. However, dedicated short-range communications (DSRC), as the sole solution so far, would meet significant challenges in the foreseeable future for supporting diverse vehicular applications simply due to the spectrum scarcity. To address this issue, in this paper, we propose an adaptive vehicular data piping framework, which is assisted by a geolocation database, for the joint utilization of DSRC and TV white space (TVWS) spectrum; in this framework, three types of vehicular data pipes (DSRC, TVWS, and cellular) are considered, while the cellular data pipe is only used as a control-plane link in coordinating the dynamic DSRC and TVWS spectrum sharing happened in the data-plane operations. In order to guarantee the optimal dynamic vehicular access to the geolocation database, we first propose a log-sum-exp (LSE) approximation-based TVWS geolocation database access approach, named LSE-WS algorithm. We formulate the adaptive vehicular data piping problem for dynamic DSRC/TVWS spectrum sharing as a coalitional formation game, and it is shown that the proposed coalitional formation approach reaches the optimal and Nash-stable vehicular data pipe selection partition in a distributed way. Through extensive simulations, we demonstrate that not only the proposed LSE-WS algorithm satisfies the dynamic vehicular geolocation database access requirement but also the adaptive multi-radio vehicular data piping approach for dynamic DSRC/TVWS spectrum sharing significantly outperforms the traditional DSRC solution.

On Employing a Savitzky-Golay Filtering Stage to Improve Performance of Spectrum Sensing in CR Applications Concerning VDSA Approach

Abstract In this paper, a filtering stage based on employing a Savitzky-Golay (SG) filter is proposed to be used in the spectrum sensing phase of a Cognitive Radio (CR) communication paradigm for Vehicular Dynamic Spectrum Access (VDSA). It is used to smooth the acquired spectra, which constitute the input for a spectrum sensing algorithm. The sensing phase is necessary, since VDSA is based on an opportunistic approach to the spectral resource, and the opportunities are represented by the user-free spectrum zones, to be detected through the sensing phase. Each filter typology presents peculiarities in terms of its computational cost, de-noising ability and signal shape reconstruction. The SG filtering properties are compared with those of the linear Moving Average (MA) filter, widely used in the CR framework. Important improvements are proposed.

Wi-Fi Hotspot at Signalized Intersection: Cost-Effectiveness for Vehicular Internet Access

In this paper, we investigate the cost-effectiveness of a Wi-Fi solution for vehicular Internet access. We define the cost-effectiveness as the cost saving by deploying and operating a low-cost Wi-Fi infrastructure instead of a costly benchmark cellular network. To characterize the service quality of Wi-Fi deployment, we also define the normalized service delay (NSD), which is the service time to fulfill a data application via the Wi-Fi network normalized by that via the cellular network. To derive the service time, we analyze the average throughput capacity of a generic vehicle in the Wi-Fi network and the average downlink capacity in the cellular network. In particular, we propose deploying Wi-Fi access point (AP) at signalized intersection and study the fundamental influence of traffic signals (which yield an interrupted vehicle traffic) on Wi-Fi access. Then, we examine the tradeoff between cost-effectiveness and NSD by identifying interplays between controllable (e.g., the density of Wi-Fi deployment and user's satisfaction) and uncontrollable parameters (e.g., vehicle traffic statistics). Our results are very useful for network operators to make strategic planning of Wi-Fi deployment for vehicular Internet Access.

Urban Revitalization of Public Spaces in the Pearl in Qatar

Qatar has witnessed a rapid development in urbanism within the last few decades especially after the oil discovery. Modern style projects have been imported to the country in-order to reflect aluxurious image. The Fareej (traditional Gulf) neighbourhood has almost disappeared and a modern lifestyle has replaced it. The Pearl Island in Qatar was one of these luxury projects contributing to the new impression. However, its social spaces lack social interaction, cohesion and vibrancy; thus, the space is less attractive except to a select group of people. Visitors are quick to notice the absence of social activities in the area, which reduces the liveability of the place. This paper focuses on investigating the social spaces of Pearl, Qatar to provide insight into what is missing and how the space could be revitalized to improve the quality of the space for users. Some recommendations are suggested to serve this aim. The paper in conclusion notes that the usage of the space can be optimised through various interventions such as hosting festivals and events in the open areas. Measures to improve thermal comfort including shading devices and thermally suited seating as well as limiting vehicular access would also help achieve the goal.

Characterizing Pervasive Vehicular Access to the Cellular RAN Infrastructure: An Urban Case Study

Managing user mobility is historically one of the most critical issues in cellular radio access networks (RANs). That task will become an even greater challenge due to cellular users on board vehicles and networked cars that autonomously access Internet-based services, whose number is expected to grow dramatically in the next few years. There is thus a need to characterize RAN access from/by vehicles in a similar way to what has been done for traditional pedestrian access. In this paper, we propose a study of the macroscopic and microscopic features of pervasive vehicular access in a case-study large-scale urban environment in the presence of realistic data sets of the road traffic and RAN deployment. We find that pervasive vehicular access is characterized by unique temporal and spatial variability in the urban region, such that it may require a dedicated RAN capacity planning: The presence of stable vehicular access load patterns and mobility flows can help to that end. Moreover, we identify the theoretical distributions that best fit key metrics for RAN planning, i.e., the vehicular users' interarrival and residence times at cells, and discuss how their parameters vary over time and space.

Reliable Adaptive Resource Management for Cognitive Cloud Vehicular Networks

In this paper, we design and test the performance of a distributed and adaptive resource management controller, which allows the optimal exploitation of cognitive radio and soft-input/soft-output data fusion in vehicular access networks. The goal is to allow energy and computing-limited car smartphones to utilize the available vehicle-to-infrastructure (V2I) WiFi connections for performing traffic offloading toward local or remote clouds by opportunistically acceding to a spectral-limited wireless backbone built up by multiple roadside units (i.e., cloudlets). We cast the resource management problem into a suitable constrained stochastic network utility maximization problem and derive the optimal cognitive resource manager that dynamically allocates the access time windows at the serving roadside units (i.e., the access points), together with the access rates and traffic flows at the served vehicular clients (i.e., the secondary users of the wireless backbone). The developed controller provides hard reliability guarantees to the cloud service provider (i.e., the primary user of the wireless backbone) on a per-slot basis. Furthermore, it is able to acquire context information about the currently available bandwidth–energy resources to quickly adapt to the mobility-induced abrupt changes in the state of the vehicular network.

A Stochastic Frontier Analysis of Technical Efficiency of Maize Production Under Minimum Tillage in Zambia

<p>Minimum tillage and other conservation agriculture practices are not only associated with income gains but are also claimed to be the panacea to the declining agricultural productivity and soil degradation problems in Africa and across the world. The few studies on technical efficiency related to the agricultural sector performance in Zambia have not attempted to determine how technically efficient smallholder farmers that produce maize under minimum tillage are. This study used stochastic frontier analysis based on both the half-normal and exponential model distributions on 2008 cross-sectional nationally representative data of 160 smallholder maize farm households that adopted minimum tillage in Zambia. Results indicate that maize farmers face increasing returns to scale (1.074) implying that there were opportunities for them to improve their technical efficiency as they were operating in stage I of their production functions. The half-normal and exponential model distributions indicate average technical efficiency scores of 60 and 71.7 percent, respectively. Their respective lowest efficiency scores were 9.3 and 8.5 percent. The highest efficiency scores for the half-normal and exponential model distributions were 89.3 and 90.9 percent. Maximum likelihood estimation results show that marital status, level of education of household head, square of household size, off farm income, agro-ecological region III, distance to vehicular road and access to loans are statistically significant factors that affect technical efficiency of smallholder maize farmers that practice minimum tillage in Zambia. The study calls for increased infrastructural development through construction of improved road network, schools and colleges in remote areas as a means to increasing accesss to knowledge and other agricultural services in order to enhance their technical efficiency levels. It also recommends promotion of minimum tillage practices in recommended agro-ecological regions to improve their technical efficiency. The study further acclaims for increased access to loans by smallholder maize farmers that practice minimum tillage as this would in one way induce them to invest in improved varieties and equipment that would help enhance their technical efficiency in Zambia.</p>