Ant colony optimization for joint resource allocation and relay selection in LTE-advanced networks

In this paper, we study the problem of optimal resource allocation in relay-assisted bidirectional LTE-Advanced networks. The bidirectional network consists of User Equipment (UE), Base Station or eNodeB (eNB) and a Relay Node (RN). We model the network by using a Two-Way Relay Channel (TWRC) in which UE and eNB can choose between different transmission schemes: direct transmission, pure CoR (CoR scheme), or via the combination of Network Coding and Cooperative Relaying (NC/CoR scheme). In this paper, an enhanced three-time-slot per cycle time-division duplexing (TDD) transmission scheme is proposed for LTE-Advanced frame architecture to accommodate the hybrid transmission scheme. We formulate the joint problem of subcarrier assignment, relay selection, and bidirectional transmission scheme selection as a combinatorial optimization problem to maximize the system total product of backlog and rate (backpressure principle). The problem is then transformed into a three-dimensional assignment problem which is solved using a hybrid ant colony optimization (ACO) algorithm. The simulation results show that our optimization algorithm significantly outperforms conventional schemes for both SISO and MIMO systems.