GPS Position Errors in VANFTS: Their Impact on a Real-World Accident Warning System

The GPS positioning system could be profitably exploited to optimize accident warning systems on VANETs. We report on extensive on-the-road experiments that we performed in Los Angeles, and discuss the influence of GPS error on both the correctness of the system and on the accuracy of the results. In the tested system the GPS error affected the detection of the position of each vehicle, both absolute and relative between the vehicles. These errors had also an influence on the dynamic measurement of the transmission range of each vehicle. Since the GPS errors are on the same order of magnitude of the size of a medium car, their effect are negligible in our experiments. The correctness of the system it is not troubled by the GPS errors, while the measurement of the reach of each alert message is affect by less than 4%. This value do not impacts on the efficacy of the tested system.