Multi-user spatial multiplexing combined with packet aggregation can significantly increase the performance of Wireless Local Area Networks (WLANs). In this letter, we present and evaluate a simple technique to perform packet aggregation in IEEE 802.11ac MU-MIMO (Multi-user Multiple Input Multiple Output) WLANs. Results show that in non-saturation conditions both the number of active stations (STAs) and the queue size have a significant impact on the system performance. If the number of STAs is excessively high, the heterogeneity of destinations in the packets contained in the queue makes it difficult to take full advantage of packet aggregation. This effect can be alleviated by increasing the queue size, which increases the chances of scheduling a large number of packets at each transmission, hence improving the system throughput at the cost of a higher delay. © 1997-2012 IEEE.

Prospective IEEE 802.11p-based vehicular surveillance system, where video from the vehicle on-board camera is transmitted to the management center, is considered. Multi-hop transmission from the vehicle to the nearest roadside unit and then-via other roadside units-to the gateway is addressed. In this letter we assess the feasibility of such system by analyzing the video end-to-end distortion for a target vehicle, located several hops away from the gateway, when it is alone or there are also other vehicles transmitting video. We demonstrate the importance of dynamic adaptation of the video bit rate of each vehicle depending on the number and positions of the participating vehicles. © 2014 IEEE.

In recently proposed cooperative overtaking assistance systems a video stream captured by a windshield-mounted camera in a vehicle is compressed and broadcast to the vehicle driving behind it, where it is displayed to the driver. It has been shown that this system can provide robust operation if video codec channel adaptation is undertaken by exploiting information from the cooperative awareness messages about any forthcoming increases in the multiple access channel load. In this letter we demonstrate the gains achievable in system performance when the video transmitter power control is also used. © 1997-2012 IEEE.

Decentralized Environmental Notification Messages (DENMs) are generated by a vehicle upon detection of an accident or other hazards on the road, and need to be promptly and reliably transmitted. Delayed or lost messages may have fatal consequences, especially in critical driving situations, such as automated overtake and emergency braking, when vehicles can be very close to each other. In this letter, the DENM latency and reliability performances are characterized over the Cellular Vehicle-to-everything (C-V2X) sidelink (PC5 interface). The conducted study uses analytical tools, among which stochastic geometry, to derive performance results, then validated by simulations. Results are applied to the case of DENMs for emergency electronic brake lights, and helpful insights are provided for this crucial case and for other more general DENM-assisted V2X use cases.

A stochastic model is designed to assess the delivery performance of event-driven safety messages in IEEE 802.11p/1609.4 vehicular ad-hoc networks (VANETs). The study focuses on the case of a vehicle detecting an unpredictable hazard and broadcasting the alert in the one-hop neighborhood. The model aims at providing quick insights into the impact of the latest WAVE specifications (i.e., traffic differentiation, channel switching) on the delivery of such short-lived alert messages. Results prove that it is accurate in capturing the effect of relevant parameters and show that repeating the alert transmission on the control channel helps to achieve reliable delivery. © 2013 IEEE.

IEEE 802.11p/WAVE (Wireless Access in Vehicular Environments) is an emerging family of standards intended to support wireless access in Vehicular Ad Hoc Networks (VANETs). Broadcasting of data and control packets is expected to be crucial in this environment. Both safety-related and non-safety applications rely on broadcasting for the exchange of data or status and advertisement messages. Most of the broadcasting traffic is designed to be delivered on a given frequency during the control channel (CCH) interval set by the WAVE draft standard. The rest of the time, vehicles switch over to one of available service channels (SCHs) for non-safety related data exchange. Although broadcasting in VANETs has been analytically studied, related works neither consider the WAVE channel switching nor its effects on the VANET performance. In this letter, a new analytical model is designed for evaluating the broadcasting performance on CCH in IEEE 802.11p/WAVE vehicular networks. This model explicitly accounts for the WAVE channel switching and computes packet delivery probability as a function of contention window size and number of vehicles. © 2011 IEEE.

We propose an analytical model that accurately captures the service advertisement and access mechanisms in IEEE 1609.4/IEEE 802.11p multi-channel vehicular networks where road-side units announce non-safety services to passing vehicles on a dedicated channel. For a drive-thru scenario, we calculate various performance measures including the service discovery probability, the mean time till discovery and the channel utilization. © 1997-2012 IEEE.

Autonomous driving in road trains, a.k.a. platooning, may reduce fuel consumption considerably if the intervehicle distances are kept short. However, to do this, the intraplatoon communication must not only be reliable but also able to meet strict deadlines. While time-triggered messages are the foundation of most distributed control applications, platooning is likely to also require dissemination of event-driven messages. While much research work has focused on minimizing the age of periodic messages, state-of-the-art for disseminating eventdriven messages is to let all nodes repeat all messages and focus on mitigating broadcast storms. We derive an efficient message dissemination scheme based on relay selection which minimizes the probability of error at the intended receiver(s) for both unicast and broadcast, without degrading the performance of co-existing time-triggered messages. We present a full analysis of the resulting error probability and delay, when relayers, selected by our algorithm, are used to disseminate messages within a platoon. Numerical results indicate that the proposed relaying policy significantly enhances the reliability for a given delay.

Relaying can increase reliability, range, or throughput. In many cyber-physical systems (CPS), relaying is used to maximize reliability before a given deadline. Since concurrent transmissions are not supported by most CPS, time-division multiple access (TDMA) is typically used. However, a major drawback of relaying in TDMA is that pre-allocated time-slots are wasted if their respective transmitters do not have any correctly received packet to relay. Therefore, in this letter, we propose a novel relay grouping scheme to overcome this drawback. Numerical results show that the proposed scheme significantly enhances the reliability while guaranteeing the deadline for each message. © Copyright 2019 IEEE - All rights reserved.

We propose a Stackelberg game based cooperative user relay assisted load balancing (LB) scheme to tackle SNR degradation problem of shifted cell-edge users which commonly occurs in a conventional direct handover LB scheme. In the proposed scheme, users from a lightly loaded cell can be selected as cooperative user-relays and will be paid by the shifted cell-edge users. Stackelberg game theory is applied to optimize the strategies of both the user relays and shifted cell-edge users, in order to maximize both of their utilities in terms of SNR and payment. Theoretical analysis and simulation study are undertaken to show the effectiveness of the proposed scheme. © 1997-2012 IEEE.

A data mining-based method for real-time detection of radio jamming Denial-of-Service (DoS) attacks in IEEE 802.11p vehicle-to-vehicle (V2V) communications is proposed. The method aims at understanding the reasons for losses of periodic cooperative awareness messages (CAM) exchanged by vehicles in a platoon. Detection relies on a knowledge of IEEE 802.11p protocols rules as well as on historical observation of events in the V2V channel. In comparison to the state-of-the-art method, the proposed method allows operating under the realistic assumption of random jitter accompanying every CAM transmission. The method is evaluated for two jamming models: random and ON-OFF. 

A method for real-time detection of Denial-of-Service (DoS) attacks in IEEE 802.11p vehicular ad-hoc networks (VANETs) is proposed. The study is focused on the "jamming" of periodic position messages (beacons) exchanged by vehicles in a platoon. Probabilities of attack detection and false alarm are estimated for two different attacker models. © 2014 IEEE

Safety and non-safety applications envisioned for Vehicular Ad hoc NETworks (VANETs) heavily rely on broadcasting for the exchange of data and status messages. New threats to road safety and efficiency raise if security requirements for broadcasting are not properly met. The decision whether or not a driver can trust information about a reported hazard should take into account the tradeoff between the decision delay, false warning probability and likelihood of missing the hazard. Although broadcasting in VANETs has been analytically studied at least for the simplified assumptions, related works do not jointly consider the reliability of the medium access control (MAC) protocol and the trust issues. In this letter, a new analytical model is designed for evaluating the latency required to guarantee trustworthiness in VANETs. This model explicitly accounts the operation of 802.11p/WAVE MAC protocol and computes mean decision delay as a function of number of vehicles, ratio of intruders as well as contention window sizes. © IEEE

Tight coupling between the performance of vehicleto-vehicle (V2V) communications and the performance of Cooperative Intelligent Transportation Systems (C-ITS) safety applications is addressed. A Cyber-Physical System (CPS) analytical framework is developed that links the characteristics of V2V communications (such as packet loss probability and packet transmission delay) with the physical mobility characteristics of the vehicular system (such as safe inter-vehicular distance). The study is applied to the Day 1 C-ITS application, Emergency Electronic Brake Lights (EEBL), enabled by ETSI ITS-G5 and IEEE 802.11p standards. © 2018 IEEE