Wireless Powered Cognitive NOMA-Based IoT Relay Networks: Performance Analysis and Deep Learning Evaluation

In this article, we study novel wireless powered cognitive nonorthogonal multiple access (NOMA)-based Internet-of-Things (IoT) relay networks to improve the performance of a cell-edge user under perfect and imperfect successive interference cancelation (SIC). In the secondary networks, a source node communicates with a cell-center user via direct link and with a cell-edge user through the assistance of a master IoT node under cognitive radio constraint. Exact closed-form analytical expressions for the outage probability (OP) of NOMA users and the overall system throughput are derived. To provide further insights, a performance floor analysis is also carried out considering two power-setting scenarios: 1) the transmit powers at the power beacon goes to infinity and 2) the maximum allowable power constraint goes to infinity. Moreover, we develop two iterative algorithms for minimizing OP users and maximizing system throughput subject to time-switching and power-allocation factors in two-hop transmission. Direct derivation of the closed-form expression for the ergodic capacity (EC) becomes unfeasible due to the high complexity of the proposed system model. To overcome this issue, we design a deep neural network (DNN) framework for the EC prediction toward real-time configurations. Our results show that the predicted results based on this DNN framework perfectly align with the simulations, validating our design framework. In addition, the DNN approach exhibits the lowest root-mean-square error and low run-time predictions among other regression models.

I. Introduction

Since the rapid development of Internet of Thing (IoT) and fifth-generation (5G) networks leads to high demands for spectral efficiency (SE), achievable data rate, massive connectivity of IoT devices, and excellent user fairness, nonorthogonal multiple access (NOMA) has been recognized as an effective solution due to its features in fulfilling such heterogeneous demands [1], [2]. By using the superimposed coding at the transmitter and the successive interference cancelation (SIC) at the receiver, NOMA can serve more users than the number of resources (time, frequency, and codes) in a nonorthogonal fashion, thus improving the SE, and promoting massive connectivity [3]. NOMA has also been applied together with wireless power transfer, which introduces a new type of self-sustainable communication in IoT systems and 5G wireless networks [4]. In [5], an energy harvesting (EH)-enabled NOMA system was studied, where multiantenna beamforming was used at the base station (BS) to maximize the energy efficiency (EE). Full-duplex relay networks with EH and NOMA were investigated in [6], where enhancing the harvested energy at the relay led to a significant performance improvement of the far user. Reshma and Babu [7] considered an EH-based incremental relaying cooperative NOMA (C-NOMA) protocol with imperfect SIC (iSIC) to show that the proposed system achieved better outage probability (OP) and throughput than the conventional EH-based C-NOMA system.