Non-orthogonal multiple access (NOMA) is a promising emerging technology that can significantly improve the utilization of spectrum and system capacity in heterogeneous wireless networks. Power allocation plays a key role in the successful deployment of NOMA. In the most prior power allocation schemes, the perfect channel state information (CSI) is assumed to be known which is difficult to obtain in a realistic environment. In this paper, we propose a power allocation scheme to maximize energy efficiency of small cells for downlink NOMA heterogeneous networks based on imperfect CSI. The system model for imperfect CSI is built, in which the optimization problem is a probabilistic non-convex problem with the constraint of outage probability. To solve the optimization problem, the probabilistic problem is transformed to a non-probabilistic problem through relaxation. The power allocation for each small cell is achieved via bisection search algorithm based on gradient value, where the trend of energy efficiency as a function of the power of the small cell is analyzed. The sequential convex programming is adapted to transform the non-convex problem to a convex problem. The closed-form solutions of power allocation factors are derived by the Lagrangian multiplier method. The simulation results show the superiority and efficiency of the proposed scheme compared with the traditional algorithms.INDEX TERMS Heterogeneous networks, non-orthogonal multiple access, power allocation, imperfect channel state information, energy efficiency.

In cellular networks, device-to-device communications can increase the spectrum efficiency, but some conventional schemes only consider uplink or downlink resource allocation. In this paper, we propose the joint uplink and downlink resource allocation scheme which maximizes the system capacity and guarantees the signal-to-noise-and-interference ratio of both cellular users and device-to-device pairs. The optimization problem is formulated as a mixed integer nonlinear problem that is usually NP hard. To achieve the reasonable resource allocation, the optimization problem is divided into two sub-problems including power allocation and channel assignment. It is proved that the objective function of power control is a convex function, in which the optimal transmission power can be obtained. The Hungarian algorithm is developed to achieve joint uplink and downlink channel assignment. The proposed scheme can improve the system capacity performance and increase the spectrum efficiency. Numerical results reveal that the performance of the proposed scheme of jointly uplink and downlink is better than that of the schemes for independent allocation.

In this paper, we propose a joint power allocation, time switching (TS) factor and relay selection scheme for an energy harvesting two-way relaying communication network (TWRN), where two transceivers exchange information with the help of a wireless-powered relay. By exploiting the TS architecture at the relay node, the relay node needs to use additional time slots for energy transmission, reducing the transmission rate. Thus, we propose a joint resource allocation algorithm to maximize the max-min bidirectional instantaneous information rate. To solve the original non-convex optimization problem, the objective function is decomposed into three sub-problems and solved sequentially. The closed-form solution of the transmit power of two sources and the optimal TS factor can be obtained by the information rate balancing technology and the proposed time allocation scheme, respectively. At last, the optimal relay node can be obtained. Simulation results show that the performance of the proposed algorithm is better than the traditional schemes and power-splitting (PS) scheme.

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In this paper, we study uplink resource allocation problem to maximize the overall system capacity while guaranteeing the signal-to-noise ratio of both D2D users and cellular users (CUs). The optimization problem can be decomposed into two subproblems: power control and channel assignment. We first prove that the objective function of power control problem is a convex function to get the optimal transmit power. Then, we design an optimal selection algorithm for channel assignment. Numerical results reveal the proposed scheme is capable of improving the system’s performance compared with the random selection algorithm.