Throughput Maximization for Wireless-Powered IoT Networks with Hybrid Non-orthognal Multiple Access

In this paper, we study a wireless-powered IoT network, where a hybrid access point (HAP) can charge internet of things (IoT) devices by wireless energy transfer technology (WET), and collect their information. To maximize the network throughput, we propose a hybrid non-orthogonal multiple access (NOMA) based transmission scheme, in which both the concurrent WET and wireless information transmission (WIT), and the non-orthogonal WIT are jointly exploited. Specifically, all devices are divided into the interference and non-interference groups, namely device grouping. During the transmission of devices in the interference group, the WET is simultaneously conducted, such that other devices harvest more energy and achieve large rates with a rate loss of devices in the interference group. Meanwhile, how to pair devices to realize the non-orthogonal WIT is also a critical issue, e.g., device pairing. Concerning the joint device grouping and pairing policy, we consider two specific hybrid NOMA based scheme, namely the first-pairing-then-grouping (FPTG) and first-grouping-then-pairing (FGTP) schemes. In the former, devices are firstly paired based on their channel qualities, and then grouped. The latter scheme is opposite. Then, we apply the order statistics to theoretically analyze the achieved performance of two transmission scheme, and the corresponding optimal pairing and grouping is determined. Finally, simulation results validate the significant improvement of the proposed hybrid NOMA based scheme in terms of network throughput.