Muhammad Awais Javed

A multi-hop broadcast protocol design for emergency warning notification in highway VANETs

Multi-hop broadcast transmission is used in vehicular ad hoc networks (VANETs) to alert all vehicles within a geographical area of an emergency situation. However, the successful dissemination of multi-hop warning messages beyond the transmission range of a vehicle faces three major issues: (i) the broadcast storm, (ii) the severe interference with the existing periodic single-hop safety messages, and (iii) the hidden nodes. In this paper, we propose an efficient time-slotted multi-hop broadcast protocol that significantly reduces the number of required transmissions, while ensuring a timely and successful delivery of the warning messages. To alleviate the broadcast storm problem, we select only a subset of vehicles on the road to serve as the potential relay nodes. Each of these ‘segment leaders’ is responsible for forwarding the warning messages arrived in its own road segment. To avoid interfering with the safety messages transmitted periodically, we propose to allocate separate time slots for the warning messages. We also devise a signaling mechanism that ensures the reliable delivery of these multi-hop messages. Simulation results confirm that the developed protocol substantially outperforms existing schemes in terms of the number of required multi-hop transmissions and the dissemination delay. At the same time, the proposed solution maintains a high reception rate and low end-to-end delay for the single-hop safety messages.

Performance analysis of an adaptive rate-range control algorithm for VANET safety applications

Vehicular Ad hoc network is considered as an important component of the next generation automotive systems. The various safety applications supported by the vehicular communication depend on the reliable delivery of the periodic safety messages. Due to variable vehicle density on the road, the fixed transmission parameters such as transmission range and packet generation rate of the safety messages result in a large number of collisions and an inefficient use of the control channel. The safety applications demand the adaptation of the above transmission parameters without compromising the safety of the vehicles. In this paper, we present a combined transmission range and packet generation rate control algorithm which takes into account the safety of the vehicles and maximizes the control channel utilization. At first, every vehicle calculates its packet generation rate using the measured time headway metric which provides a measure of the vehicle safety. In the second step, the transmission range is adapted based on the vehicle density estimation, the target network load and the packet generation rate of each vehicle. The performance analysis shows that the proposed algorithm improves the safety message performance in terms of packet reception rate and control channel utilization for a range of vehicle densities and vehicle speeds.

Joint space-division multiple access and adaptive rate control for basic safety messages in VANETs

In a vehicular ad hoc network (VANET), basic safety messages (BSM) are exchanged among vehicles to provide cooperative awareness and support safety applications. While the periodic generation and transmission of such messages already place a heavy burden on the network load, the hidden nodes further complicate the network situation with packet collisions being undetectable. In this paper, we propose a space-division multiple access (SDMA) technique combined with an adaptive rate control mechanism to improve the efficiency of BSM transmissions. With SDMA to reduce the interference among the vehicles and address the hidden-node problem, only vehicles located sufficiently far apart are allowed to reuse the same time slot to send their BSMs. The developed SDMA approach permits multiple transmissions per road segment and uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) in each segment, giving rise to a much better use of both space and bandwidth. To guarantee that the actual number of BSM transmissions does not exceed the maximum allowable, we devise an adaptive scheme that optimally adjusts the individual packet generation rates in accordance to the vehicle density. Toward this end, we find an optimal bandwidth utilization that maximizes the newly-defined metric, termed as “safety throughput” per vehicle. Such an optimal utilization allows a large number of BSM packets to be generated while maintaining a high reception probability. Our comprehensive simulation results confirm the clear advantages of our proposal over the existing techniques, in terms of safety range, BSM packet inter-arrival time, and safety throughput.

A Cooperative Safety Zone Approach to Enhance the Performance of VANET Applications

Safety applications in VANETs relies on various type of information exchanges among vehicles of which Cooperative Awareness Message (CAM) has the largest share in the network load due to their periodic broadcast nature. As the vehicle density grows, the load generated by the CAMs could increase beyond the transmission capacity of a VANET resulting in the loss of neighborhood information and a higher utilization of the control channel. In this paper, we present the concept of a safety zone to adaptively control the transmit power of CAMs to restrict the network load without compromising the safety features of VANET applications. Moreover, we also introduce a new cooperative information sharing technique to increase the vehicles awareness beyond the transmission range. The simulation results show that the proposed technique could significantly reduce the packet losses and channel utilization for a range of vehicle densities.

A geocasting technique in an IEEE802.11p based vehicular ad hoc network for road traffic management

In future, vehicular networks will play a crucial role in the development of intelligent road traffic systems. Vehicular network will enable cars to exchange crucial road traffic information among them as well as with the traffic signaling infrastructure. In an ad hoc vehicular network generally broadcasting technique is used to disseminate road traffic information. In an IEEE802.11p based vehicular network broadcasting technique could increase the contention level thus increasing information dissemination delay. In this paper we propose a geocasting packet transmission technique to transmit safety messages in a vehicular network which can significantly improve the QoS of a vehicular network. In this work OPNET based simulation models are used to analyze the performance of the proposed protocol. The proposed protocol performance is benchmarked against the standard packet broadcasting protocols proposed for vehicular networks.

Security in Intelligent Transport Systems for Smart Cities: From Theory to Practice

Connecting vehicles securely and reliably is pivotal to the implementation of next generation ITS applications of smart cities. With continuously growing security threats, vehicles could be exposed to a number of service attacks that could put their safety at stake. To address this concern, both US and European ITS standards have selected Elliptic Curve Cryptography (ECC) algorithms to secure vehicular communications. However, there is still a lack of benchmarking studies on existing security standards in real-world settings. In this paper, we first analyze the security architecture of the ETSI ITS standard. We then implement the ECC based digital signature and encryption procedures using an experimental test-bed and conduct an extensive benchmark study to assess their performance which depends on factors such as payload size, processor speed and security levels. Using network simulation models, we further evaluate the impact of standard compliant security procedures in dense and realistic smart cities scenarios. Obtained results suggest that existing security solutions directly impact the achieved quality of service (QoS) and safety awareness of vehicular applications, in terms of increased packet inter-arrival delays, packet and cryptographic losses, and reduced safety awareness in safety applications. Finally, we summarize the insights gained from the simulation results and discuss open research challenges for efficient working of security in ITS applications of smart cities.

Multimedia Transmission for Emergency Services in VANETs

Emergency warning applications in a vehicular ad hoc network (VANET) requires successful dissemination of warning notification within a geographical area spanning multiple hops. Multimedia transmission provides an accurate overview of the emergency event in the form of an image, an audio or a video. However, the reliable transmission of emergency multimedia messages using multi-hop broadcast techniques suffer from broadcast storm and severe interference from the existing periodic single-hop safety messages. In this paper, we propose an efficient time-slotted multi-hop broadcast protocol for emergency multimedia transmission. To avoid interference with the safety messages already in place, we propose to allocate separate multi-hop time slots for the multimedia messages, and devise a signaling mechanism that ensures a reliable delivery of these multimedia messages. The proposed mechanism can also handle the scenario of lost acknowledgment (ACK) and thus effectively reduce the unnecessary retransmissions of the multimedia messages. Simulation results confirm that the developed protocol substantially outperforms existing schemes in terms of both the number of required multi-hop transmissions and the dissemination delay, while maintaining a high reception rate and a low end-to-end delay for the single-hop safety messages.

Measuring safety awareness in cooperative ITS applications

Cooperative Intelligent Transportation Systems (C-ITS) are key component of the future road traffic management system. To evaluate and analyze the reliability of various applications supported by C-ITS, realistic performance metrics are required. Such metrics serve as a performance indicator and help in tuning the wireless transmission parameters to maintain required quality of service. The essential purpose of a C-ITS is to enhance the vehicle safety awareness and hence, provide an accurate information of vehicles in the vicinity through regular sharing of cooperative awareness messages (CAMs). The existing metrics such as packet delivery ratio provide quantitative measure of vehicle safety awareness but do not consider the accuracy of received information. In this paper, we propose two novel safety awareness metrics (SAM) to enhance the measure of vehicle awareness by considering factors such as age and weight of a received CAM in the perspective of C-ITS. Using simulation results in NS-3, we show that the current metrics provide an optimistic view of vehicle safety awareness and proposed metrics serve as a valuable gauge to analyze the reliability of applications in C-ITS.

Performance analysis of a time headway based rate control algorithm for VANET safety applications

Vehicular ad hoc network is considered as an integral part of the future intelligent transportation system. As the number of applications which are supported by the vehicular communication grow, the efficient utilization of the control channel and congestion control become important issues. The periodic broadcast of basic safety messages (BSM) by the vehicles consumes most of the control channel interval, leaving less transmission capacity for other types of traffic. To accommodate the data packets from other safety and non-safety applications, the packet transmission rate of BSM must be controlled without compromising the safety of the vehicles. In this paper, we present a BSM generation rate control algorithm based on the measured time headway of the vehicles. The performance analysis shows that the proposed rate control algorithm reduces the channel utilization and improves the BSM reception ratio at different vehicle densities and vehicle speeds. Moreover, the proposed rate control algorithm effectively reduces the notification time of a multi-hop warning message.

On the Interrelation of Security, QoS, and Safety in Cooperative ITS

Cooperative intelligent transport system (C-ITS) is an emerging technology that enables secure and safe road travel using wireless communications. Vehicles regularly share their mobility information with the neighborhood road traffic and infrastructure-based road side units using cooperative awareness messages (CAMs) to develop a local dynamic map for safety applications. Since the applications provided by C-ITS are related to human safety, reliable as well as secure communications are required. To protect the vehicular network from untrusted data of malicious users that could cause network congestion and reduce vehicle safety, ITS standards have proposed various security procedures. In this paper, we analyze the interrelation between security, quality of service (QoS), and safety awareness of vehicles in C-ITS. To formulate an accurate measure of vehicle safety awareness, we first propose novel vehicle and infrastructure centric metrics that use the number of received CAMs, their accuracy, safety importance, and vehicle heading. We then implement the standard CAM signature and verification procedure in the ITS standard. Using simulation results and our proposed metrics, we show the impact of security signature and verification speed on the level of vehicle awareness and, hence, QoS in different road traffic conditions.