Abstract-Interference and traffic imbalance hinder the improved system performance in heterogeneous ultra-dense networks. Network cooperation becomes a promising paradigm with sophisticated techniques which can significantly enhance the performance. In this article, a coalition game-theoretic framework is introduced to characterize the cooperative behaviors, and thus exploring these cooperative benefits and diversity gains. First, we introduce the basis of the coalition games, and then we survey its latest applications, in particular, the interference mitigation and traffic offloading. Different from most of the current applications, we concentrate on the cooperative incentive mechanism design since the node cooperation always means resource consumption and other costs. Moreover, for the incentive mechanism, a cooperative spectrum leasing is introduced. To mitigate the interference and balance traffic, we propose two schemes under the presented framework: interference alignment with spectrum leasing (IASL) and traffic offloading with spectrum leasing (TOSL). Simulation results show the improved performance of the cooperative gains using the proposed IASL and TOSL schemes.