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Spectrum sensing and sharing the sensing results is one of the most important tasks for the operation of a cognitive radio network. It is even more crucial in a multi-hop cognitive radio network, where there is no omni-present central authority. But since communicating the sensing results periodically to other users consumes significant amount of energy, users tend to conserve energy by not sharing their results. This non-cooperation will lead to lesser clarity in spectrum occupancy map. Therefore, appropriate strategies are required to enforce cooperative sharing of the sensing results. The classic Tit-For-Tat strategy cannot be used because punishing a node by not broadcasting the sensing results also affects other nodes. In this paper, we address this problem by exploiting the unique characteristics of cross-layer interaction in cognitive radios to sustain cooperative spectrum sensing. In this direction, we design a Cross-Layer game which is a combination of the spectrum sensing game in the physical layer and packet forwarding game in the network layer. In this strategy, users punish those who do not share their sensing results by denying to cooperate in the network layer. The Cross-Layer game is modeled as a noncooperative non- zero-sum repeated game and a Generous Tit-For-Tat strategy is proposed to ensure cooperation even in the presence of collisions and spectrum mobility. We prove that the Nash Equilibrium of this strategy is mutual cooperation and that it is robust against attacks on spectrum sensing and sharing session.