The employment of IEEE 802.11p-compliant devices in the automotive environment is crucial to traffic safety and control applications. Thus, performance evaluation of the standard before its widespread adoption in real systems is of paramount importance. Nonetheless, due to the high cost and reasonably low availability of off-the-shelf devices, most of the work involving IEEE 802.11p vehicular networks is still based on simulations. In order to investigate the distance to real-world equipment, this work investigates the results of experimentation with commercial devices, in V2I (Vehicle-to-Infrastructure) and V2V (Vehicle-to-Vehicle) scenarios. The performance obtained by real on-board and road-side units is then compared to those presented by widely used NS-3 simulator. Three key metrics are evaluated: the maximum range, packet delivery rate (PDR), and packet inter-reception time (PIR). The influence of different modulations defined in IEEE 802.11p and of different mobility levels are analyzed. For both simulation and experimentation, the results agree on the PDR degradation at intense vehicle speeds and higher PHY data rates. Nevertheless, the results in terms of maximum range, moderate speed impact, and the weak correlation between the PIR and PDR show that NS-3 simulation models still need to evolve.

Vehicular communications based on IEEE,802.11p promise to improve traffic efficiency and safety in the near future. Embedded with 802.11p-compliant devices, the cooperation among connected vehicles will provide a shift in the way transportation systems operate. Nevertheless, before widespread adoption, extensive performance evaluation of the standard is in need. Due to the high cost and reasonably low availability of commercial devices, most work on VANETs is still performed using simulations. To investigate the equivalence between real experiments and simulations involving 802.11p, this article evaluates the behavior obtained by periodic beacon messages, the basis of safety applications in VANETs. Using commercial OBUs and RSUs, the results are compared with those obtained with NS-3/PhySim and Veins/MiXiM simulators. In V2I and V2V communication scenarios, three key metrics are evaluated: the maximum communication range, packet delivery rate, and packet inter-reception time. The influence of different modulations supported by 802.11p and varying vehicle speeds are also analyzed.

The association of elevated rail structures and Maglev (magnetic levitation) trains is a promising alternative for urban transportation. Besides being cost-effective in comparison with underground solutions, the Maglev technology is a clean and low-noise mass transportation. In this paper, we propose a low-cost automatic braking system for Maglev trains. There is a myriad of sensors and positioning techniques used to improve the accuracy, precision and stability of train navigation systems, but most of them result in high implementation costs. In this paper, we develop an affordable solution, called Redundant Autonomous Safe Braking System (RASBS), for the MagLev-Cobra train, a magnetic levitation vehicle developed at the Federal University of Rio de Janeiro (UFRJ), Brazil. The proposed braking system employs GNSS (Global Navigation Satellite System) receivers at the stations and trains, which are connected via an ad-hoc wireless network. The proposed system uses a cooperative error correction algorithm to achieve sub-meter distance precision. We experimentally evaluate the performance of RASBS in the MagLev prototype located at the campus of UFRJ, Brazil. Results show that, using RASBS, the train is able to dynamically set the precise location to start the braking procedure.

Intelligent Transportation Systems (ITS) are based on the intelligence placed on roadside units and onboard vehicles. ITS technologies, like connected cars, improve road safety by having vehicles communicating with each other, with the infrastructure, or both. The communication uses the 5.9 GHz band, called Dedicated Short Range Communications (DSRC), and protocols defined in the Wireless Access in Vehicular Environments (WAVE) architecture. This paper evaluates, through practical experiments with latest on-board units (OBUs), the performance of a forward collision warning (FCW) application operating in the DSRC control channel number 178. The application uses location information provided by an internal high-precision GPS to calculate the safe braking distance from a vehicle moving towards a stationary vehicle. Experiments were conducted at speeds of 30, 40, 50 and 60 km/h with a GPS update rate of 5 Hz. Our results show a margin of error below 1%, demonstrating the required reliability to forward collision avoidance applications.