Mixed Mode Transmission and Resource Allocation for D2D Communication

In cellular communication systems with optional device-to-device (D2D) links, user equipments (UEs) can operate in either D2D mode or cellular mode for data transport. This work introduces mixed-mode D2D communication in which D2D links can operate in multiple modes through resource multiplexing. Within this framework, we study the problem of maximizing weighted D2D sum rate under cellular rate constraints by optimizing mixed-mode allocation and resource allocation in term of transmit power and subchannel assignment. Due to nonconvex cellular rate constraints and binary constraints of subchannel allocation, this problem is a nonconvex mixed-integer problem that is generally difficult to solve. We propose a two-step approach by introducing energy-splitting variables such that mixed-mode allocation and resource allocation can be decoupled and optimized independently. The resulting algorithm can be distributive, requires little signaling overhead, and has low computational complexity. We present extensive numerical results to demonstrate the practicality of our proposed algorithm with regard to various network parameters.