Hybrid transmission scheme and relay selection in LTE-Advanced network: Graph-based approach

This paper proposes a dynamic resource block allocation scheme in relay-assisted bidirectional LTE-Advanced networks which consists of three nodes: User Equipment (UE), Base Station or eNodeB (eNB) and an intermediate Relay Node (RN). In this work, an enhanced three-time-slot per cycle time division duplexing (TDD) transmission protocol is proposed to the LTE-Advanced frame architecture. In such a protocol, UEs and the eNB can choose between different transmission schemes: direct transmission, pure Cooperative relaying (CoR scheme) using an intermediate relay station, or via the combination of Network Coding and Cooperative Relaying (NC/CoR scheme). A graph-based framework is proposed to solve the NP-hard combinatorial optimization problem. Our problem is transformed into a maximum weighted clique problem and used to provide optimal achievable rate regions for the hybrid transmission scheme, resource block assignment and relay selection. The proposed hybrid transmission scheme determines the best transmission strategy among direct transmission, CoR and NC/CoR in each three-time-slot cycle based on the system channel information as well as the queue length information. The simulation results show that our optimization algorithm significantly outperforms conventional schemes for both SISO and MIMO systems.