  Small cells in the millimeter wave band densely deployed underlying the
macrocell have been regarded as one of promising candidates for the next
generation mobile networks. In the user intensive region, device-to-device
(D2D) communication in physical proximity can save power and improve spectral
efficiency. In this paper, we focus on the optimal sub-channel allocation for
access and D2D links in the scenario of densely deployed multiple mmWave small
cells. The problem is modeled as a coalitional game to maximize the system sum
rate of access and D2D links in the system. Then we propose a coalition
formation game based algorithm for sub-channel allocation. Performance
evaluation results demonstrate superior performance in terms of the system sum
rate compared with other practical schemes.
