The IEEE 802.11p standard operates with the WAVE (Wireless Access in Vehicular Environments) system in vehicular ad hoc networks (VANETs). The broadcast process is used to send messages for safety and non-safety applications. A previous work on broadcast packets over the control channel proposes an analytical model to study the loss process. Even if such work does not consider all of the phenomena affecting the operation of vehicular networks, we can obtain a very good approximation of the performance that VANETs may exhibit. Regardless of its importance, this subject has been barely studied. Moreover, there is in the literature only a couple of contributions on this subject, being both analytical models. Therefore, we present in this paper an analysis of the loss process of broadcast packets on the control channel of VANETs over different scenarios. First, we consider a typical two-way scenario and then we analyze a scenario with intersections, both for different vehicle densities. We conduct a campaign of extensive simulations with the NS-3 simulator to study the average loss rate of broadcast packets, and then we compare our results with an analytical model proposed by Campolo et al. We prove the relationship among the contention window, the packet size, and the number of vehicles with the loss rate, including losses caused by noise, collisions, hidden terminal, and channel switching. Thus, we analyze the loss process validating the results obtained by Campolo et al. We find that there are additional factors affecting the loss rate, which cannot be captured with the analytical model. One key finding in this work is that the loss rate due to channel switching differs between both approaches. Also, we find bounds on the use of the control channel, with the loss rate and the traffic load in the network as parameters.
A Cooperative Communication Protocol for QoS Provisioning in IEEE 802.11p/Wave Vehicular Networks