The large-scale networks is studied to raise physical layer security of NOMA networks in [29] to enhance the security of a random network and such a system adopts a protected zone around the source node. To evaluate the performance of transmission using a stochastic geometry model, mmWave NOMA networks with random beamforming was investigated in [30]. A downlink transmission with spatially random users is proposed in cooperative NOMA using Decode-and-Forward mode [31]. Both half-duplex and full-duplex for NOMA network are determined under a model of stochastic geometry and in which the authors further evaluate the performance of a pair of relay selection schemes [32]. Although most papers in the literature have explored the NOMA networks, lack of evaluation in case of random locations of users. For example, the results in [13; 14; 15] only consider the static models wherein the static locations of users are assumed. To the best of the authors' knowledge, few works examine the situation of random interference surrounding users. More specifically, the location of interference is random in practical and related investigations are very limited. We note that the authors in [32] did not evaluate the situation of degradation in the performance of two user pairing strategies under the impact of external interference. They provided two user pairing modes, namely random and distance-based user pairing. For a specific user pairing strategy, we employ tools from stochastic geometry to derive the outage probability of the downlinkNOMA scheme. However, open problems as the interference surrounding users are generally operated in any location. In the literature, various works have been conducted to capture the randomness of the surrounding interferers via Poisson point process (PPP) [33; 34; 35; 36]. Moreover, [PERSON] et al. [36] studied the cooperative relaying networks in which the interference influence the performance at each relay. The interference model in [36] subjected to spatial separation constraints, in which each relay needs to be distant from one another otherwise inadvertently leads to high performance loss [37]. Due to the many applications of NOMA, the paired users are usually separated in terms of distance, e.g., a cell-center and a cell-edge user, thus making it feasible to implement the Poisson interference models into consideration. Therefore, it is necessary to examine the dynamic location of interference which is located near users in the scenario of downlink NOMA. This study benefits the evaluation of cellular networks on mobile users who met degraded performance. In particular, surrounding interference sources can be examined by statistic methods and then the quality of cellular network is in control by mobile service providers. The main contributions of our work can be summarized as follows:  
* We analyze a downlink NOMA network with the degraded performance by randomly distributed interferers located near to users and the number and positions of interferers follow independent PPP. Closed-form expressions of outage probability for the proposed system are given. * We provide transmit antenna selection schemes, i.e., random antenna selection (RAS) and Best Antenna Selection (BAS), which enable us to improve the quality of transmission and evaluate performance gap on these schemes. * Lower bound of ergodic capacity and upper bound of outage probability happen at RAS mode for such system model. Moreover, improvement ergodic capacity can be observed via optimal ergodic capacity achieved by heuristic search method. The density of interference make a crucial impact on both outage probability and ergodic capacity performance. The remainder of this paper is organized as follows. The system model of NOMA as random interference existing near two users is described in Section 2. In Section 3, the Random Antenna Selection (RAS) mode at the base station is introduced via two metrics, i.e., outage probability and ergodic capacity. The best antenna serving each user is presented in Section 4.