# Ecological Dynamics and Evolution of Cooperation in Vehicular Ad Hoc Networks
## 2 Related Work
[17] proposed a game-theoretic model for cooperation in VANETs that considers the impact of obstacles on communication. [PERSON] et al. [19] proposed a cooperative transmission mechanism that considers the impact of obstacles and interference on transmission rates. The problem of promoting cooperation in social dilemmas involving groups of interacting individuals is traditionally investigated using the Public Goods Game (PGG), which assumes that individuals can make contributions to a public good. In VANETs, the data packet can be considered as the public good. [PERSON] and [PERSON] were the first to propose a game theoretic strategy, called Tit-for-Tat, to promote cooperation among vehicles in VANETs based on PGG. Their approach measured the cooperation level of the vehicles based on time and the number of message forwards, and they examined the effect of different parameters on the cooperation level to evaluate the performance of the proposed game [21]. In a different study, [PERSON] et al. used PGG to investigate cooperative behavior among vehicles [13]. They showed that the cooperation level in VANETs is proportional to the synergy factor. [PERSON] and [PERSON] proposed a PGG framework to analyze the effects of networking properties on the dynamics of cooperation in VANETs. In another work, [PERSON] et al. designed a PGG for VANETs with high node density. In the proposed game, vehicles could dynamically adjust their grouping strategy according to the real situation around their strategies. Additionally, they defined a hub vehicle that exchanges data packets with all neighbors to prevent isolated vehicles. The authors demonstrated that increasing the multiplication factor in the PGG would promote the cooperation level, which is an expected result for VANETs [22]. In VANETs, messages sent by vehicles and road side units can impact multiple vehicles. Thus, it is more appropriate to model the effect of event messages as a multiplayer game with collective interactions rather than pairwise. However, current PGG-based models in VANETs have limitations. Researchers usually assume that each vehicle has fixed neighbors or can perfectly connect to all other players, which is not realistic in VANETs. Additionally, the topology of vehicles does not change throughout the game, which is also unrealistic. In VANETs, a vehicle benefits from diffusible messages produced by all vehicles in its group, which randomly form at each generation. Therefore, the vehicle's payoff should be calculated by weighting the payoffs obtained in the randomly composed groups, weighted by the probability that such groups occur. Moreover, in VANETs, the PGG is played in populations of varying sizes. Small population size (or density) results in small group sizes and vice versa for a larger population size. To address these limitations, this study models vehicles as players that form randomly composed groups at each round of the game based on the population size. This game is called ecological-aware PGG. The study investigates, for the first time to the best of our knowledge, the effect of rate of departure and density of vehicles on the cooperation dynamics in VANETs based on ecological-aware PGG.