To meet the drastic growth of mobile traffic, next-generation wireless networks integrate existing technologies such as dual-connectivity (DC) and network-assisted device-to-device (D2D) communications. In this paper, we present a new spectrum allocation scheme for a heterogeneous system, which incorporates both technologies. For the effective collaboration of individual network agents, we employ the ideas of cooperative games, and the spectrum allocation algorithm is implemented as a novel

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... t-bargaining process. Based on the bargaining solutions of classical Nash, weighted Nash, and Nash bargaining with coalition structure, our three-step interactive approach can leverage the full synergy of different bargaining concepts. Under the dynamic changing HetNet environments, we can take various benefits in a rational way while handling comprehensively the DC-based D2D communication issue and reach an agreement that gives mutual advantage. The main novelty of our proposed scheme is to ensure a relevant tradeoff between conflicting requirements during HetNet operations. Finally, we conduct extensive simulation study and illustrate that the proposed scheme provides a considerable performance improvement by comparison with the existing protocols.