Fast and reliable communication between vehicles is a key factor in improving the transportation safety. To enable such communication, the two main competing technologies are Cellular V2X (C-V2X or LTE-V2X) and IEEE 802.11p-based DSRC. This paper presents a comparison between the performance of C-V2X and DSRC in dense highway scenarios. C-V2X and DSRC implementations considered here are compliant to SAE J3161/1 and SAE J2945/1 standards, respectively. The results show that with a similar bandwidth of 10 MHz, in terms of both inter packet gap (IPG) and reliability, C-V2X performs better than DSRC at ranges greater than 100m, while both technologies exhibit good performance at shorter distances. Additionally, with SAE J3161/1-based one-shot transmissions for critical events, C-V2X performance at shorter distances is further enhanced. Moreover, with the larger bandwidth of 20 MHz, C-V2X further improves in performance.

This paper presents an in-depth performance comparison between several C-V2X (LTE-V2X) configurations in congested highway scenarios in 10 MHz and 20 MHz channels. Specifically, we focus on the inter-packet gap (IPG) performance, which is a key metric used in several V2X related studies. IPG measures the delay between two successfully received transmissions from a particular device. The results show that significant performance gains in terms of IPG can be achieved using the probabilistic one-shot transmission mechanism specified in SAE J3161/1 standard, which dictates that vehicles randomly skip their reserved Semi-Persistent Scheduling (SPS) transmissions and send one-shot transmissions instead. Furthermore, we conclude that this IPG gain with J3161/1 probabilistic one-shot transmissions can be achieved without any significant impact in terms of packet reception rate (PRR) performance.

In Vehicular Ad-hoc Networks (VANETs), fast and reliable dissemination of safety messages is a key step toward improving the overall road safety. In a highly dynamic VANET environment, safety message dissemination in a multi-hop manner is a challenging and complex problem that has gained significant attention recently. Many protocols and schemes have been proposed to efficiently share safety messages among vehicles. However, most existing techniques do not perform well under real-world traffic conditions, or perform adequately only under very limited scenarios and traffic conditions. This research proposes a highly efficient and reliable multi-hop broadcasting protocol, Intelligent Forwarding Protocol (IFP), that exploits handshake-less communication, ACK Decoupling, and an efficient collision resolution mechanism. In this research, IFP has been extensively studied and evaluated to establish its robustness and superiority over existing schemes. A key contribution of this paper is to present an in-depth analysis and optimization of IFP using theoretical modeling, thorough simulations, and extensive real-world experimentation. With IFP, the message propagation delay is significantly reduced and packet delivery ratio is drastically improved.

For human-driven as well as autonomous vehicles, one of the key requirements is continuous awareness of the surroundings to detect any potential threats (vehicles, pedestrians, wild-life etc.). This requires continuous cooperation between the vehicles by efficiently sharing safety information in a timely manner. However, this is a multi-dimensional and challenging problem due to the complex nature of the vehicular environment. To solve this problem, this paper proposes an elegant solution to efficiently share the safety information among vehicles by using only Basic Safety Messages (BSM), which are part of the existing V2V standards. Through this research, the vehicles are able to quickly and preemptively identify potential threats, not only in their close proximity, but also those which are further along the roadway by intelligently exchanging safety information between neighboring vehicles. Additionally, for the first time, the proposed architecture presents a practical approach of incorporating the onboard sensor data with the V2V communications. This leads to vehicles having improved visibility and situational awareness further outside of their one-hop coverage. Simulation results show that improved visibility of vehicles up to 2.6 km can be achieved while placing minimum overhead and complexity on the network.

Sharing emergency messages amongst vehicles on the road can greatly reduce traffic accidents. In Vehicular Ad Hoc Networks (VANETs) to share these emergency messages, fast and reliable message dissemination is the key objective in a highly dynamic VANET environment. This research proposes a novel broadcasting protocol to achieve these goals by introducing handshake-less broadcasting, ACK Decoupling and efficient collision resolution mechanism. A key contribution of this paper is to analyze and optimize the broadcasting algorithm using thorough mathematical modeling with extensive simulations. With the suggested optimization process, the message propagation delay can be significantly reduced.

Vehicular Ad Hoc Networks (VANETs) is an extension of Mobile Ad Hoc Networks (MANETs) to share traffic information and emergency alerts amongst vehicles on the road. To support many applications in VANETs, most studies use GPS to find the furthest node with ACK to ensure successful message reception. However, this ACK procedure can be removed if a channel between the sender and receiver is clear such that the sender can overhear the broadcasted messages from the receiver. If the sender fails, nodes closer to the sender inform the sender of successful rebroadcasting, which serves as an ACK to the sender. This process will either entirely remove costly ACKing processes or at least decouple the messages propagation from ACKing to the sender, which will significantly improve the speed of message propagation. In this paper, we use Signal-to-Noise Ratio (SNR) with ACK decoupling to ensure fast message propagation with reliable message recovery. Detailed simulation results show that the proposed SNR based approach with ACK decoupling outperforms the Smart Broadcast (SB) by 200% in average throughput and per hop delay, while ensuring the reliable dissemination of emergency messages in typical VANETs environments.