Transmit-Power Minimization for NOMA-enabled Traffic Offloading with Security Provisioning

IEEE Non-Orthogonal Multiple Access (NOMA) has been proposed as an effective technique to cope with the enormous mobile traffic in wireless communication networks in a spectrum-efficient manner. Meanwhile, to further relieve the traffic pressure, 3GPP has proposed Dual-Connectivity (DC), through which each Mobile User (MU) can simultaneously communicate with the macro cell and small cell. In this letter, we investigate the transmit-power minimization problem for DC-based traffic offloading in downlink NOMA systems while taking the security provisioning into account. The proposed power allocation problem is difficult to solve due to natural nonconvexity. In spite of this, we transform it into an equivalent traffic scheduling problem by exploiting the feature of DC. The transformed traffic scheduling problem is proved to be a Monotonic Optimization (MO) problem which can be solved by the Polyblock Approximation (PA) method. Numerical results are provided to demonstrate the performance and advantages of our proposed traffic offloading scheme with security consideration.