A number of timer-based intelligent flooding schemes have been recently proposed to optimise message dissemination in Vehicular Ad-hoc NETworks. Unfortunately, most of them are not able to completely avoid useless copies of the message to be broadcast. Moreover, some schemes determine when the message has to be rebroadcast, thus thwarting the application in processing it. The use of a Medium Access Control (MAC) layer control packet handshake allows mitigating the issues above, but it could lead to an unacceptable overhead and to a high probability of dissemination interruption. The proposed Data-Ack Scheme (DAS) allows to reduce the overhead by exploiting only one control packet and makes the dissemination interruption most unlikely. By simulation, DAS performance has been compared with that obtained when either a MAC layer handshake-based scheme or a scheme which does not provide the use of control packets is adopted. Simulation results have shown that DAS performs better in those scenarios in which the Message Delivery Ratio values are not critical.

This paper proposes an algorithm to be used in IEEE 802.16e networks for adapting MAC PDU size to wireless channel behavior when ARQ is adopted at MAC layer. The algorithm is based on an analytical approach for dynamically evaluating the optimal packet size. The latter is derived from an expression of the ARQ protocol efficiency, obtained by exploiting a finite-state Markov error model which also takes into account Adaptive Modulation/Coding. The effectiveness of the designed algorithm in improving TCP performance has been evaluated.

A number of Intelligent Flooding Schemes have been recently proposed in order to optimize message dissemination in Vehicular Ad Hoc Networks. In this paper we focus on a scheme which exploits a distributed timer-based contention mechanism for allowing only contention winners to forward the message and to suppress other potential forwarders. In particular, at each hop along the message propagation direction, potential forwarders wait for a time which is inversely proportional to their distance from the sender before rebroadcasting the packet; a potential forwarder is suppressed if it intercepts the packet rebroadcasted by another node during the waiting time. Performance of the scheme, in terms of message delivery ratio, delay and channel utilization, depends on the maximum waiting time (MaxWT) and on the maximum distance R allowed between the sender and a potential forwarder. This research work aims at evaluating an optimal setting of these parameters. We show that, although the values of MaxWT and R which maximize performance vary with traffic load and vehicle density, a dynamic algorithm is not essential. Then, we report how to set the values of the parameters to achieve a performance that is acceptable in the scenarios which we have considered.

Vehicular communications could be exploited for energy management of vehicles. We propose a system which provides that a vehicle estimates its future speed profile gathering status messages broadcasted by the surrounding vehicles and/or the infrastructure and inputting them in a traffic simulator used as a predictor. The system has been validated by simulation considering an urban scenario inspired to the Ecotekne campus at the University of Salento and a Manhattan scenario, very challenging in relation to the prediction of the speed profile. Simulation results have shown that the prediction error is quite low for the first scenario. In the Manhattan scenario, the error is quite high in case each vehicle limits itself to send messages only to its neighbours and does not transmit the information regarding its route. However, the error can be significantly reduced if route information is broadcasted and the infrastructure relays the messages transmitted by vehicles. The proposed system has been tested in the Ecotekne campus.

Abstract: Information and Communication Technologies could play a very important role in order to optimize the energy management of conventional, hybrid and electrical vehicles and, thus, to reduce their environmental impact. In particular, vehicular communications could be used to predict driving conditions with the objective to determinate future load power demand. To this, we propose a system which allows to estimate future speed profile on board of a vehicle by gathering state messages that surrounding vehicles and/or infrastructure broadcast and by inputting them to a traffic simulator (SUMO) used as a predictor. The system has been validated by a simulation model which considers a number of vehicles moving on the road network of the Ecotekne campus at the University of Salento. The actual speed profile of a target vehicle has been compared with that estimated on board for prediction horizon duration values ranging from 1 s to 60 s. Simulation results have shown that, even if the horizon duration is set to 60 s, the prediction error, in terms of the root mean square, is lower than 4 km/h. Afterwards, the system has been implemented on real vehicles and its functionalities have been tested in the campus road network