Localization issues in the use of ITS

Abstract

The problem to rectify and optimize distance measures from satellites in GNSS devices has been thoroughly explored in many researches. Instead there is not much information on available procedures to replicate the observed errors. The replication of GNSS errors can, in fact, be useful in many traffic simulation scenarios to test for ITS performances. The purpose of this article is to present cases where such a methodology can be useful and then introduce a methodology for the explicit simulation of errors in GNSS systems. The proposed methodology is based on the experimental analysis of some statistical distributions. Such distributions, arising from multiple observations in the field, are able to reproduce the behavior of the error in time as a function of the factors that influence it. The analyzed data were extracted by the GPS/GLONASS sensors of common smartphones and compared with a high-precision GPS equipment. These data were evaluated in different signal coverage conditions, in an open field where the signal quality is expected to be better, suburban and urban areas, where the signal is expected to be worse. The analysis considers many aspects such as the signal reflection problems and the sudden loss of the signal because of a change of the received satellite constellation. The research was conducted by following various steps: a field survey through smartphones and high-precision instrumentation in different conditions, the creation of reference distributions for each parameter that can have an influence on the error, the analysis of correlation functions between the variables, and a final implementation of the proposed algorithm coupled with microsimulation. The paper intends to shed some light on this problem allowing scientist and developers of new ITS system methodologies to reproduce in a simulated environment not only the movement of single vehicles (as usually carried on with microsimulation) but also the data that could be obtained from on-vechicle GNSS instrumentation. The reproduction of this GNSS tracks can be useful to assess the overall response of some new ITS systems before implementing them in the field. The proposed simulation methodology could become a standard tool to help in making better decisions in ITS implementation and to develop better ITS systems.