Elsevier

Ad Hoc Networks

Volume 79, October 2018, Pages 133-145
Ad Hoc Networks

On vehicular safety message transmissions through LTE-Advanced networks

https://doi.org/10.1016/j.adhoc.2018.06.016Get rights and content

Abstract

Long Term Evolution Advanced (LTE-A), which provides high data rates with low latencies, can be an alternative to IEEE 802.11p for supporting vehicular applications. In this paper, we propose two solutions for the uplink transmission of safety messages: a new scheduler and a safety message generation rate adaptation. These solutions consider the speed of vehicles for resource allocation or selection of message generation rates, to provide the same level of location information accuracy on the central server for all vehicles. For downlink, we investigate the possible methods for delivering safety messages to the relevant vehicles, and propose a resource-efficient scheme based on broadcasting.

We also propose a scheme that uses both LTE-D2D and LTE-cellular communication for transmission of safety messages. Vehicles transmit their safety messages with longer periods to the central server. This location information is used to determine the possible D2D pairs, as well as centralized resource allocation for the following period. Vehicles use the allocated resources for transmission of their safety messages to their neighboring vehicles using D2D communication. The simulation results show the effectiveness of our solutions in the cellular-only approach. These results also show that the proposed D2D-cellular scheme can reduce the required resources, while satisfying the requirements of safety applications.

Introduction

Last year, more than 94 million vehicles were produced around the world [1], and the total number of vehicles worldwide is more than one billion [2]. The World Health Organization (WHO) reported that more than 1.25 million people were killed in road accidents last year [3]. The increasing number of cars on the road and a high number of road fatalities have motivated the automotive industry and research community to find solutions for increasing road safety. To this end, the Intelligent Transportation System has been proposed by introducing a network of connected cars, known as Vehicular Ad-hoc NETworks (VANET). A significant amount of research has resulted in the development of IEEE 802.11p, which is a variant of the IEEE 802.11 standard. Although IEEE 802.11p provides some needed features such as low overhead, support of high-speed users, and less dependence on infrastructure, it suffers from scalability issues, unbounded delays, and short radio range. Moreover, despite vast research on the standardization of IEEE 802.11p, it has not yet been widely deployed in the real world, with only some pilot projects and prototypes in existence [4], [5], [6], [7].

Exploiting already existing technologies, such as cellular networks, has motivated researchers to evaluate the possibility of using these networks to support vehicular applications. Several studies have assessed the performance of different mobile networks to support vehicular applications [8], [9], [10], [11], [12]. Long Term Evolution (LTE) and its enhancement LTE-Advanced (LTE-A) are the most outstanding deployed access networks, providing high data rates with low latencies. LTE/LTE-Advanced also support high-speed terminals and can cover larger areas. Preliminary results show that LTE/LTE-A can be an alternative access network for vehicular communications [13], [14], [15]. However, the performance of LTE for applications with strict requirements, such as safety applications that are very sensitive to latencies, is still under investigation. Thus, some modifications are needed to make LTE more suitable for such applications.

There are three categories of vehicular applications: traffic efficiency, safety, and infotainment [16]. In this paper, we focus on safety applications that aim to make roads safer by reducing fatalities. This goal is achieved by the transmission of safety messages between neighboring vehicles. ETSI (European Telecommunications Standards Institute) introduced two types of safety messages: periodic and event-triggered messages [17]. The latter are transmitted to report hazardous events such as crashes on the road. The former, aka Cooperative Awareness Messages (CAMs) or beacons, contain necessary information about the vehicle, such as location, speed, acceleration, direction, etc., and are periodically broadcast to the neighboring vehicles to raise their awareness about the environment. In our work, we focus on these types of messages.

There are different possible schemes for transmitting safety messages in an LTE-based network. Two types of communications are present in the LTE network: cellular communications, in which data should pass through the eNB and infrastructure to deliver to another user; and direct D2D communications, which allow users to directly transmit their data to each other without involvement of the infrastructure. According to these two types of communication, there are three possible schemes for handling the transmission of safety messages in LTE networks. The strategies are to use only cellular communications, only D2D communications, or a combination of both.

When using cellular-only communications, vehicles transmit their safety messages to the server in the backbone of the network. The server extracts the information and forwards to vehicles neighboring the transmitter. The network load on uplink depends on the safety message size, message generation periods, and number of vehicles. Some levels of congestion may occur when the load of the network is greater than the available bandwidth. In this situation, some vehicles have to wait longer to get transmission resources. This leads to larger delays for some vehicles, which affects the location information accuracy of vehicles on the server. Another parameter affecting the location accuracy is speed of the vehicles. Faster vehicles travel a longer distance in the same time; thus, they are more vulnerable to latency. We show that using traditional LTE schedulers and considering fixed message generation periods for all vehicles are not suitable for safety applications.

We propose two solutions to tackle this issue. On the LTE side, we propose a new scheduler, which takes into account the vehicles’ speed and the last time their message was received at the server for resource allocation. Thus, faster vehicles obtain resources before slower vehicles. The other solution is an adaptation of safety message generation periods. We propose an algorithm that considers speed of the vehicles and available bandwidth to adapt the message generation periods. Both solutions increase the location accuracy of faster vehicles (which is low in normal situations) by giving higher priority to them in resource allocation (in the scheduler case) or letting faster vehicles transmit safety messages more frequently (in the period adaptation case). Hence, all vehicles experience a similar level of location accuracy at the server.

In the downlink, we present three possible approaches for delivering safety messages to the corresponding vehicles. The server can determine these vehicles based on the previously received information. In the unicast mode, the server transmits received message separately to vehicles neighboring the transmitter. Although the delay is reduced. Since the server forwards messages as soon as they are received, this mode generates lots of load on the downlink and is not resource efficient. In the second mode, the server forms a multicast group of vehicles neighboring the transmitters, and multicasts the message to them. This method is more resource efficient. However, some delays occur with the creation of multicast groups, as these groups change quickly. The last approach for delivery of safety messages is broadcasting. The server aggregates the received messages from these vehicles and broadcasts the aggregated message to the cell. Each vehicle receives the message and uses the relevant information. The broadcast mode is more resource efficient, however, server needs to wait for messages from all vehicles to aggregate them into one message. This can add some delays to message reception.

Direct D2D communication is introduced in 3rd Generation Partnership Project (3GPP) release 12 [18], which is aka LTE-A. This feature allows devices in proximity to one another to establish a direct connection and transfer data without passing through the infrastructure. However using only D2D communications for safety message transmission is not a proper solution. First, as the vehicular environment is highly dynamic, the D2D pair changes quickly and vehicles should consume lots of energy to actively discover vehicles in their proximity. Second, the initial time required to establish D2D communication is too long for safety applications. We propose a scheme that relies on both cellular and D2D communications. Vehicles transmit their safety messages with a longer period to the server, using cellular communications. The location information at the server is used for D2D pair detection and resource allocation. In the following period, vehicles use the established D2D connections and allocated resources to transmit their safety messages to neighboring vehicles. With our resource allocation algorithm, vehicles are categorized into subsets. Transmission of vehicles in each subset does not produce any interference on other vehicles in that subset. Thus, the same resources can be allocated to all vehicles in a subset, increasing the reusability of the resources.

The main contributions of this paper are summarized as follows:

  • 1.

    We propose two solutions for safety messages transmission in uplink direction of LTE. The first solution is a scheduler that prioritizes vehicles for resource allocation. The second one is an algorithm that adapts vehicles safety message rates based on their speed. These solutions provide similar level of location previsions for all vehicles regardless of their speed.

  • 2.

    We present different possible schemes for delivering the safety messages in downlink direction and discussed about their advantages and disadvantages.

  • 3.

    We propose a scheme which relies on LTE-D2D communications to transmit safety messages. An efficient algorithm is proposed for resource allocation that increases the reusability of resources. We also discuss the effect of the time period that vehicles use for updating their location on the central server on resource usage and accuracy of neighboring determination.

The rest of this paper is organized as follows. Section 2 presents state-of-the-art research on LTE for vehicular applications. The transmission of safety messages using only cellular communications is described in Section 3. In Section 4, we present two solutions for safety message transmission in uplink direction of LTE. In Section 5 we present our proposed scheme, which uses both cellular and D2D communication for transmission of safety messages. Section 6 presents some simulation results to evaluate the performance of different solutions. Finally, Section 6 concludes this paper.

Section snippets

State of the art

Many studies have discussed and evaluated the concept of using the mobile network (e.g., cellular networks) to support vehicular applications [8], [9], [10], [11], [13], [14], [15], [19]. The European Telecommunications Standards Institute (ETSI) published a technical report [8] to introduce a framework for public mobile networks in Cooperative Intelligent Transport Systems (ITS). This report evaluated the performance of different generations of cellular networks (i.e., GSM, UMTS, and LTE) in

Cellular communication for vehicular safety message transmission

The first scheme that we describe in this paper is to use only cellular communications for transmission of vehicle safety messages. Every communication is performed through the LTE network infrastructure. Thus, this approach contains two parts: transmission of safety messages toward a central server in uplink direction and delivering the received safety messages to vehicles in the awareness area of that transmitter in the downlink direction. In this Section, we first describe the procedure of

Solutions to improve the cellular-based scheme

The transmission of safety messages in the uplink can suffer from congestion problems, which lead to substantial delays that are not suitable for safety applications. In fact, the freshness of information at the server is a key factor that relies on safety messages generation rate and network latencies. Higher message generation rates mean more fresh information which provides more accurate location information. On the other hand, larger latencies mean less fresh information and less accurate

D2D communication for vehicular safety messages transmission

Although the approach of using only LTE cellular connections, as introduced in the previous section has some advantages, such as collection of the data at the server, it suffers from scalability and congestion issues. Increasing the number of vehicles in the cell or when vehicles transmit the safety messages with higher rates (i.e., lower period) to improve the location information accuracy, the load on the network increases dramatically. Due to the limited number of available radio resources,

Proposed D2D scheme for vehicular safety messages transmissions

As mentioned above, there are two types of discovery. Direct discovery is suitable for scenarios in which some users are only transmitting (service providers), and some users are only receiving (service clients). In these situations, the service provider (e.g., shopping store) transmits discovery signals periodically to announce its presence. On the other hand, other users listen to the discovery channel to detect users in their proximity. As in vehicular scenarios, each vehicle acts as both

Performance evaluation

In this Section, we present simulation results to evaluate the performance of safety message transmission through an LTE-based network in different scenarios. Table 1 summarizes the parameters that are used in the simulation.

Conclusion

In this paper, we present an approach that uses only LTE cellular communication. In this approach, vehicles transmit their safety messages to a central server in the uplink, which forwards back the messages to vehicles neighboring of the transmitting vehicle. When the network load is high, congestion may occur, causing long delays for some vehicles. These delays lead to higher location information error of vehicles (especially faster vehicles) on the server. We proposed a scheduler which

Mr. Hossein Soleimani obtained his B.Sc. and M.Sc. degrees in Electrical Engineering in 2009 and 2011 from Sharif University of Iran. He is currently a Ph.D. candidate at the School of Electrical Engineering and Computer Science, University of Ottawa, Canada and studies under the supervision of Professor Azzedine Boukerche as a member of PARADISE research group. His main areas of research interest consist of cellular networks and mobile/vehicular ad hoc networks.

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    Mr. Hossein Soleimani obtained his B.Sc. and M.Sc. degrees in Electrical Engineering in 2009 and 2011 from Sharif University of Iran. He is currently a Ph.D. candidate at the School of Electrical Engineering and Computer Science, University of Ottawa, Canada and studies under the supervision of Professor Azzedine Boukerche as a member of PARADISE research group. His main areas of research interest consist of cellular networks and mobile/vehicular ad hoc networks.

    Azzedine Boukerche (FIEEE, FEiC, FCAE, FAAAS) is a full professor and holds a Canada Research Chair position at the University of Ottawa (Ottawa). He is the founding director of the PARADISE Research Laboratory, School of Information Technology and Engineering (SITE), Ottawa. Prior to this, he held a faculty position at the University of North Texas, and he was a senior scientist at the Simulation Sciences Division, Metron Corp., San Diego. He was also employed as a faculty member in the School of Computer Science, McGill University, and taught at the Polytechnic of Montreal. He spent a year at the JPL/NASA-California Institute of Technology, where he contributed to a project centered about the specification and verification of the software used to control interplanetary spacecraft operated by JPL/NASA Laboratory. His current research interests include wireless ad hoc, vehicular, and sensor networks, mobile and pervasive computing, wireless multimedia, QoS service provisioning, performance evaluation and modeling of large-scale distributed systems, distributed computing, large-scale distributed interactive simulation, and parallel discrete-event simulation. He has published several research papers in these areas. He served as a guest editor for the Journal of Parallel and Distributed Computing (special issue for routing for mobile ad hoc, special issue for wireless communication and mobile computing, and special issue for mobile ad hoc networking and computing), ACM/Kluwer Wireless Networks, ACM/Kluwer Mobile Networks Applications, and Journal of Wireless Communication and Mobile Computing. He has been serving as an Associate Editor of ACM Computing Surveys, IEEE Transactions on Parallel and Distributed systems, IEEE Transactions on Vehicular Technology, Elsevier Ad Hoc Networks, Wiley International Journal of Wireless Communication and Mobile Computing, Wiley’s Security and Communication Network Journal, Elsevier Pervasive and Mobile Computing Journal, IEEE Wireless Communication Magazine, Elsevier’s Journal of Parallel and Distributed Computing, and SCS Transactions on Simulation. He was the recipient of the Best Research Paper Award at IEEE/ACM PADS 1997, ACM MobiWac 2006, ICC 2008, ICC 2009 and IWCMC 2009, and the recipient of the Third National Award for Telecommunication Software in 1999 for his work on a distributed security systems on mobile phone operations. He has been nominated for the Best Paper Award at the IEEE/ACM PADS 1999 and ACM MSWiM 2001. He is a recipient of an Ontario Early Research Excellence Award (previously known as Premier of Ontario Research Excellence Award), Ontario Distinguished Researcher Award, Glinski Research Excellence Award, IEEE CS Golden Core Award, IEEE Canada Gotlieb Medal Award, IEEE ComSoc Expectional Leadership Award, IEEE TCPP Exceptional Leadership Award. He is a co-founder of the QShine International Conference on Quality of Service for Wireless/Wired Heterogeneous Networks (QShine 2004). He served as the general chair for the Eighth ACM/IEEE Symposium on Modeling, Analysis and Simulation of Wireless and Mobile Systems, and the Ninth ACM/IEEE Symposium on Distributed Simulation and Real-Time Application (DS-RT), the program chair for the ACM Workshop on QoS and Security for Wireless and Mobile Networks, ACM/IFIPS Europar 2002 Conference, IEEE/SCS Annual Simulation Symposium (ANNS 2002), ACM WWW 2002, IEEE MWCN 2002, IEEE/ACM MASCOTS 2002, IEEE Wireless Local Networks WLN 03–04; IEEE WMAN 04–05, and ACM MSWiM 98–99, and a TPC member of numerous IEEE and ACM sponsored conferences. He served as the vice general chair for the Third IEEE Distributed Computing for Sensor Networks (DCOSS) Conference in 2007, as the program co-chair for GLOBECOM 2007–2008 Symposium on Wireless Ad Hoc and Sensor Networks, and for the 14th IEEE ISCC 2009 Symposium on Computer and Communication Symposium, and as the finance chair for ACM Multimedia 2008. He also serves as a Steering Committee chair for the ACM Modeling, Analysis and Simulation for Wireless and Mobile Systems Conference, the ACM Symposium on Performance Evaluation of Wireless Ad Hoc, Sensor, and Ubiquitous Networks, and IEEE/ACM DS-RT.

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