Performance Measurement of a Bluetooth-based Floating Car Observer

Resumen

The Bluetooth-based Floating Car Observer (FCO) is a traffic monitoring approach which is based on detections made by floating traffic observers using wireless radio-based technologies such as Bluetooth while passing other traffic objects (vehicles, cyclists, pedestrians). For the evaluation of the performance of a Bluetooth-FCO it is crucial to know how likely it is that a detectable traffic object (i.e. with Bluetooth device on board) within the detection range will be monitored. The major point to answer this question is the inquiry process which sets up the connection between Bluetooth devices and which can take up to several seconds. Given the possibly high speed of the vehicles and the relatively small detection range this poses a major problem to this detection mechanism. The paper focusses on the analytical evaluation of the time it takes an observer to discover traffic objects nearby. Therefore, the device discovery process is described as an exponential distribution, that is, the number of detections based on Bluetooth is a sequence of independent respectively seen or not seen trials each of which occurs with a certain probability. This follows from the assumption that the number of vehicles equipped with Bluetooth devices and the number of observer vehicles within the network is small, so that the chances to encounter are statistically independent events. To analytically evaluate the performance of the monitoring process, simulations as well as laboratory and field experiments with Bluetooth receivers and senders were conducted to measure detection rates as a function of inquiry times.