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Adjusting transmission power and packet generation rate of periodic status information messages in VANETs

In Vehicular Ad Hoc Networks (VANETs), each node can benefit of the periodic transmission of one-hop broadcast messages containing status information (e.g., position, speed) by all other nodes in a common wireless channel. Thus, safety applications can make use of collected information in order to assist drivers and avoid dangerous road situations, detecting them before they become critical. Clearly, the semantic requirements of safety applications necessary to ‘achieve safety’ must be mapped into communication protocols’ configuration parameters. In this study we extend the work in [1] in order to provide an answer to two essential questions required by anyone intending to build an automotive safety system based on wireless communications: i) how many status information updates should be sent every second to the wireless medium?, and ii) which transmission power should be used?. Due to technology limitations (see [2]), the existing tradeoffs need to be appropriately balanced in order to find the optimal point of operation. While higher packet generation rates can increase the information accuracy with frequent updates, an uncontrolled strategy can lead to a saturated medium with a high rate of message collisions. Likewise, although a message sent with higher transmission power can reach further distances, it also increases the level of interferences on other transmissions. Additionally, a higher transmission power could increase the robustness of a specific message transmission. Indeed, in real mobile environments the attenuation of the signal amplitude can vary over time and in different vehicular environments due to radio propagation phenomena. Our purpose is to first understand the causes of reception success and failure of one-hop broadcast messages in realistic vehicular scenarios. For this reason, we classify the packet arrival states in six disjoint categories with respect to the signal and interference power level and study them under different vehicular traffic, channel load, and radio wave propagation conditions. Second, we propose a set of performance metrics together with our methodology to complete an appropriate framework that, once safety requirements are ‘well defined’, can assist in the process of mapping applications’ semantic requirements into optimal configuration values of the communication system.