Roadside units allocation algorithms for certificate update in VANET environments

The roadside unit (RSU) plays an important role in VANET environments for privacy conservation. In order to conserve the privacy of a vehicle, the issued certificate must be updated frequently via RSUs. If a certificate expires without being updated, the services for the vehicle will be terminated. Therefore, deploying as more as possible RSUs will ensure that the certificate can be updated before it expires. However, the cost for allocating an RSU is very high. In this paper, we consider the roadside unit allocating problem such that the certificates can be updated before it expired. Previous researches focus on the roadside unit placement problem in a small city in which for any origination-destination pair the certificate is limited to update at most once. The scalable RSUs placement problem in which more than once certificate updates are required is discussed in this paper. The RSUs allocation problem is formulated and is proved as an NP-hard problem. We proposed two scalable roadside unit placement algorithms which works well for a large city. Simulation results show that the proposed algorithms yields lower number of required RSUs than the simple method named the most shortest path counts first method.