# Efficient Resource Management for Sum Capacity Maximization in 5G NOMA Systems
## 1 Introduction
### Related Work  
Optimization of resource management for NOMA transmission has been studied extensively in literature. For instance, the authors of Reference [12] formulated a resource management problem to enhance the sum capacity of two-user NOMA system. The proposed framework first guarantees the minimum quality of service (QoS) of one mobile user and then allocate the remaining power to other mobile user to maximize the overall system capacity. A price based power optimization scheme was presented in downlink wireless network [13]. The objective was to maximize the revenues and average achievable rate of the proposed network by adopting game theoretic approach. To deal with non-convex optimization, they decouple the problem and use alternating optimization algorithm to obtain the efficient solution. The research in Reference [14] provided a low complexity power allocation to enhance the weighted sum capacity in downlink NOMA systems. They considered two cases, namely a two-use case and a multi-user case and exploited low complex and closed form solutions to solve the non-convex optimization. [PERSON] et al. in Reference [15] proposed a Karush-Kuhn-Tucker (KKT) based solution for power management to enhance the sum capacity of the network subject to a minimum user rate. [PERSON] et al. in Reference [16] investigated the outage performance and ergodic capacity for downlink NOMA network. Under the constraint of interference threshold from the secondary system to the primary system, the power management problem for capacity enhancement and outage probability in two-user cognitive radio NOMA network was proposed in Reference [17]. A proportional fairness scheduling approach was considered for fair power allocation to maximize the sum rate and maximize the minimum of normalized rate in a two-user network [18]. [PERSON] et al. proposed the channel estimation and power management problem for two-user system to maximize the average effective signal to interference plus noise ratio (SINR) of the strong user with bounded average effective SINR of the weak user [19]. To maximize the effective sum capacity with delay QoS constraint, [PERSON] et al. provided a sub-optimal solution based on truncated channel inversion power control in a two-user downlink system [20]. In addition, resource optimization techniques for NOMA in multi-cell communications networks have also been investigated [3; 21; 22; 23; 24; 25; 26]. In Reference [21], a KKT-based efficient power management technique was presented by [PERSON] et al. to enhance the sum capacity of multi-cell multi-user NOMA network. In similar study, a KKT-based closed form solution for power optimization was provided by [PERSON] et al. in multi-cell network to minimize the total system power and maximize the system sum capacity [22]. The study in Reference [23] considered a downlink heterogeneous network (HetNet) based on power multiplexing. The authors formulated a non-convex optimization problem to improve the network capacity and outage probability. They provided sub-optimal algorithm for user scheduling and power allocation. A problem for optimal power allocation was investigated in HetNet based on power multiplexing [24]. The objective of the research was to increase to the network throughput subject to users QoS requirements. They adopted a distributed power approach based on Stackelberg equilibrium. To improve the fairness among different users and enhance the sum rate of the system,Zhao et al. provided an efficient resource management scheme in HetNet [25]. They exploited matching theory for sub-channel assignments to different small-cell BSs and sequential convex programming based on KKT conditions for power allocation at different BSs. [PERSON] et al. in [3] provided energy efficient resource management in NOMA HetNet. They first transformed non-convex optimization to a convex problem and then employed dual method for sub-channel and power allocation. In another study, [PERSON] et al.