Resource allocation in mixed mode Device-to-Device communications

In Device-to-Device (D2D) enabled cellular networks, user pairs can select either direct mode or regular cellular mode for data transport. The optimum choice varies depending on power constraints, channel conditions, and QoS requirements. This work proposes a mixed-mode resource allocation strategy through which user pairs can multiplex different modes with disparate resource fraction and transmission power. We study the problem of maximizing D2D sum rate under cellular rate constraint. Successive convex approximation (SCA) algorithm is applied to solve the resulting non-convex joint optimization problem. Our theoretical analysis indicates that mixed-mode achieves superior performance over commonly adopted single mode selection. We further show the advantages of mixed-mode resource allocation in improving cellular rate constrained D2D link performance through extensive numerical tests.