Impact of CCA threshold, contention window, and transmit rate on VANET simulations

Channel access in vehicular networks (VANETs) according to the IEEE 802.11p standard relies on CSMA/CA. The specific challenge lies in optimizing the reception rate of broadcast messages carrying awareness information about neighboring vehicles. Several studies have focused on algorithms and protocols that control the channel access in vehicular ad hoc networks, often with a focus on performance analysis of a specific algorithm under certain simulation model assumptions. Among the parameters that influence simulation results, the clear channel assessment (CCA) threshold is a parameter, which is often overlooked. While having low impact in under-utilized channels, the CCA threshold can change the perception of the channel load resulting in interfering transmissions, which in turn have a negative impact on reception rates at larger distances. In this work we investigate the variation of CCA threshold, contention window, and transmit rate for different vehicle densities and demonstrate the impact on received packets at certain distances as well as on the overall channel load.