Cooperative pseudonym change scheme based on the number of neighbors in VANETs

In Vehicular Ad hoc NETworks (VANETs), trigger-based pseudonym change schemes play an important role in providing anonymity. However, the anonymity provided by these schemes usually is low mainly because the behavior of changing pseudonym is individual. Considering cooperation on changing pseudonym can enhance anonymity, in this paper, we give a general cooperation framework. As an application of the framework, we present a Cooperative Pseudonym change scheme based on the number of Neighbors (CPN). We generally analyze the anonymity provided by the CPN scheme and qualitatively compare the scheme with its corresponding scheme without cooperation, Non-CPN (NCPN). Then, under uniform traffic distribution, we develop an approximate analytical model for CPN in relatively simple one-lane VANETs to analyze the anonymity. Finally, we investigate the anonymity of CPN in one-lane and multi-lane VANETs by simulation. The results show that the ratio of the size of anonymity set in multi-lane to that in one-lane VANETs, first quickly goes up, then slowly decreases a bit, and at last approaches the value of number of lanes. In addition, the improved performance of CPN over NCPN reaches peak when the average number of neighbors approaches that number in the trigger.