  In the paradigm of mobile Ad hoc networks (MANET), forwarding packets
originating from other nodes requires cooperation among nodes. However, as each
node may not want to waste its energy, cooperative behavior can not be
guaranteed. Therefore, it is necessary to implement some mechanism to avoid
selfish behavior and to promote cooperation. In this paper, we propose a simple
quid pro quo based reputation system, i.e., nodes that forward gain reputation,
but lose more reputation if they do not forward packets from cooperative users
(determined based on reputation), and lose less reputation when they chose to
not forward packets from non-cooperative users. Under this framework, we model
the behavior of users as an evolutionary game and provide conditions that
result in cooperative behavior by studying the evolutionary stable states of
the proposed game. Numerical analysis is provided to study the resulting
equilibria and to illustrate how the proposed model performs compared to
traditional models.
