Speed-aware vehicle grouping for reducing the load on the spectrum database

The spectrum database provided by FCC and Ofcom stores information about the availability of channels that can be used by vehicles to reliably transfer safety traffic information. However, due to the large number of queries to the database, the query delay could increase. In previous models, numerous modes of operation have been designed, but the communication between vehicles of different modes (particularly, Mode I and Mode II according to FCC terminology) is not discussed. Developed models for estimating the load on the database were based on the assumption that all vehicles travel at the same velocity, which is not a realistic condition for proper database load analysis. In this paper we address this issue by proposing an approach that divides the roads into segments and assigns a car or two to play the role of a Mode II covering the whole segment. The assigned vehicle(s) are responsible for providing the cars in their segments with the queried spectrum information. To test the validity of our design, we evaluate its performance using Matlab simulations based on the mathematical model we developed for estimating the number of Mode II cars. We illustrate how the database load varies in response to changes in various system parameters, such as number of segments, number of cars, and speed of vehicles.