Energy-Efficient NOMA-Enabled Traffic Offloading via Dual-Connectivity in Small-Cell Networks

The recent small-cell dual-connectivity (DC) in 3GPP specification enables a mobile user (MU) to communicate with the macrocell and offload traffic through a small cell, which facilitates a flexible traffic offloading. The advanced non-orthogonal multiple access (NOMA) further enables small/macro cells to simultaneously accommodate multiple MUs' offloading using the same channel, which improves spectrum-efficiency. In this letter, driven by the growing demand for greening cellular systems, we investigate the energy-efficient NOMA-enabled traffic offloading through DC, which aims to minimize the total power consumption of the small and macro cells, while satisfying each MU's QoS-requirement. The optimal traffic offloading corresponds to a two-sided power allocation problem, which, however, is nonconvex. By exploiting the feature of DC, we equivalently transform this power allocation problem into a convex rate-splitting problem, which can be efficiently solved. Numerical results are provided to validate the advantage in saving power consumption by using the proposed optimal NOMA-enabled traffic offloading scheme.