Optimal Mode Selection by Cross-Layer Decomposition in D2D Cellular Networks

Direct communication among user equipments, called Device-to-Device (D2D) communication, is envisioned in academia and industry to enhance future cellular networks for increased spectral efficiency. Mode selection considers the question which links should be offloaded to use direct communication mode and is one of the core questions in D2D research. In this work, we ask the question which information needs to be exchanged between a remote mode selection controller and Medium Access Control (MAC) layer to allow optimal operation without the burden of a full-fledged cross-layer optimization. We formulate mode selection as utility maximization with cross-layer decomposition and solve it using the Generalized Benders Decomposition technique. The result is a nested offloading structure, in which the network controller regularly updates its mode selection decision while in the meantime, the network operates in a particular fashion, gathering information to enable better future mode selection decisions. We show that the proposed structure allows achieving an optimal mode selection configuration within a finite number of optimization steps for any non-negative utility function. Due to our general network model, the solution is applicable to a variety of system set-ups, including overlay and underlay D2D, with and without power control and single or multi-antenna systems.