Spectral and Energy-Efficient Wireless Powered IoT Networks: NOMA or TDMA?

Abstract

Wireless powered communication networks (WPCNs), where multiple energy-limited devices first harvest energy in the downlink and then transmit information in the uplink, have been envisioned as a promising solution for the future Internet-of-Things (IoT). Meanwhile, non-orthogonal multiple access (NOMA) has been proposed to improve the system spectral efficiency (SE) of the fifth-generation (5G) networks by allowing concurrent transmissions of multiple users in the same spectrum. As such, NOMA has been recently considered for the uplink of WPCNs based IoT networks with a massive number of devices. However, simultaneous transmissions in NOMA may also incur more transmit energy consumption as well as circuit energy consumption in practice which is critical for energy constrained IoT devices. As a result, compared to orthogonal multiple access schemes such as time-division multiple access (TDMA), whether the SE can be improved and/or the total energy consumption can be reduced with NOMA in such a scenario still remains unknown. To answer this question, we first derive the optimal time allocations for maximizing the SE of a TDMA-based WPCN (T-WPCN) and a NOMA-based WPCN (N-WPCN), respectively. Subsequently, we analyze the total energy consumption as well as the maximum SE achieved by these two networks. Surprisingly, it is found that N-WPCN not only consumes more energy, but also is less spectral efficient than T-WPCN. Simulation results verify our theoretical findings and unveil the fundamental performance bottleneck, i.e., "worst user bottleneck problem", in multiuser NOMA systems.

Computation Efficiency Maximization in Wireless-Powered Mobile Edge Computing Networks

“…The simulation parameters are selected based on the works in [5], [6] and the parameters for the nonlinear EH model are selected based on [32]. Similar to [30]- [35], the reference distance is set as 1 meter and the maximum services distance for users is 5 meters. The channel power gains are set the same as those in [30].…”

“…Thus, (15) is proved. Based on (30) and (15), the following cases can be obtained. When g k < w opt , t k = 0 since Γ (λ k , ρ k , β, θ k , g k ) < 0; when g k > w opt , Γ (λ k , ρ k , β, θ k , g k ) < 0 holds when ρ k > 0.…”

Energy consumption optimization for self‐powered IoT networks with non‐orthogonal multiple access

“…The duration of a time slot T is set to 0.1 s. Both the channel power gains h m and g m are modeled as 10 −3 2 d − , 15 where 2 is an exponentially distributed random variable with unit mean and d m is the distance. All IoT devices in the network are identical, and have the same settings, including m = 0.4, 42 p c m = 0.1mW, 41 and N m = 1000 bit. 15 Referred to typical NB-IoT systems, 41 the carrier frequency is 750 MHz and the bandwidth is 180 kHz.…”

“…15 Referred to typical NB-IoT systems, 41 the carrier frequency is 750 MHz and the bandwidth is 180 kHz. All IoT devices in the network are identical, and have the same settings, including m = 0.4, 42 p c m = 0.1mW, 41 and N m = 1000 bit. The constant coefficient is set to 1.2 × 10 −8 W/bit.…”

Generalized Wireless-Powered Communications: When to Activate Wireless Power Transfer?

“…Future vehicles are envisioned to be equipped with massive numbers of on-board sensors to achieve reliable inter-vehicle communications and accurate navigation. To eliminate the inconvenience caused by conventional manual battery charging and tangled wires, wireless power transfer (WPT) has gained an unprecedented upsurge of interest due to its capability to provide devices with controllable amounts of energy via radio frequency (RF) signals [1]- [3]. The advancement of vehicular networks has also fueled the development of various applications based on WPT, e.g., unmanned aerial vehicles (UAV) with WPT functionality may power Internet-of-Things (IoT) devices (e.g., sensors embedded in bridges) [4].…”