Sum Rate Maximization for Multi-User Wireless Powered IoT Network With Non-Linear Energy Harvester: Time and Power Allocation

Abstract

We consider the ''harvest-then-transmit'' protocol in a wireless powered communication network (WPCN), where an energy-constrained access point (AP) harvests energy from the radio-frequency signals transmitted by a power beacon (PB) for assisting user data transmission. In the wireless information transfer (WIT) phase, AP employs the harvested energy to convey independent signals to multiple users through either time-division multiple access (TDMA) or orthogonal frequency-division multiple access (OFDMA). Aiming to maximize the sum rate (SR) of the WPCN, we jointly optimize the energy harvesting (EH) time and the AP power allocation, considering both the conventional linear and practical nonlinear EH models at the AP. The optimization problems of both TDMA-and OFDMA-enabled WPCNs are formulated as nonconvex programs, which are challenging to solve globally. To achieve an efficient optimal solution to the problem of TDMA-enabled WPCN, we first decompose the original nonconvex problem into three convex subproblems, and then propose a low-complexity iterative algorithm for its solution. For the OFDMA-enabled WPCN, the problem belongs to a difficult class of mixed-integer nonconvex programming due to the involvement of binary variables for subcarrier allocation. To overcome this issue, we convert the problem to a quasi-convex problem and then employ a bisection search to obtain the optimal solution. Simulation results are provided to confirm the benefit of jointly optimizing the EH time and the AP power allocation compared to baseline schemes. The performance of the proposed TDMAenabled WPCN is shown to be superior to that of the proposed OFDMA-enabled WPCN in terms of SR when the transmit power of PB and the number of antennas of AP are relatively large.INDEX TERMS Wireless powered communication networks, time-division multiple access, orthogonal frequency-division multiple access, non-linear EH, IoT, nonconvex optimization.

Resource Allocation for AF Relaying Wireless-Powered Networks With Nonlinear Energy Harvester

“…Consequently, SWIPT systems are practically suited for short-range communications. As an alternative, the power beacon (PB)-based technique has been proposed to support wireless power transfer (WPT) systems [3]- [5]. Low-cost PBs can be deployed much closer to wireless-powered devices to improve the system efficiency.…”

“…For the EIT scheme, the duration of the WIT phase is divided into equal intervals (i.e., τ 1 = τ 2 = ... = τ K = (1 − τ 0 )/K) [12]. For the FET scheme, the EH duration is fixed as τ 0 = 0.1, τ 0 = 0.5, τ 0 = 0.9 [3]. The two parameters ς, and ℘ represent the search accuracies of the bisection method for searching the optimal e * k and the golden search method for finding the optimal τ * 0 , respectively.…”

“…Proposed Iterative Algorithm for Solving (T-P1) Initialize: τ l = 0, τ h = 1, step ζ =[3], and ℘ is a given error tolerance. 2: repeat 3:…”

Resource Allocation for Energy Efficiency in OFDMA-Enabled WPCN

“…However, in disaster situations, such energy sources may not be a viable approach due to destrustion. Therefore, wireless power transmission using radio frequency (RF) to charge for energy-constrained devices is a promising solution for low-power wireless networks [1]- [5]. In [4], a hybrid power transfer architecture was proposed where airships, helicopters, and balloons are deployed as power supply sources to transfer energy wirelessly via inductive power transfer to large communication devices and via microwave power transfer to small communication devices.…”

“…However, the authors only focused on describing the proposed hybrid power transfer procedure without providing any mathematical analyses. The authors in [5] investigated the sum-rate of an IoT wireless powered communication network (WPCN), while the energy efficiency (EE) of the network was not considered.…”