Information Rate-Harvested Power Tradeoff in THz SWIPT Systems Employing Resonant Tunnelling Diode-based EH Circuits

TL;DR

This paper addresses the rate-harvested power tradeoff in THz SWIPT by deploying RTD-based energy harvesting at the receiver and unipolar ASK at the transmitter. It introduces a novel non-linear, piecewise RTD EH model built from 5-parameter logistic segments, and derives both an optimal and several suboptimal TX input distributions to maximize mutual information under harvested-power and peak-amplitude constraints. A monotonic equivalent EH model is used to enable tractable optimization, with a discretized algorithm (and a closed-form alternative) to compute the input distributions; closed-form results are also provided for the low-power regime. Numerical results, validated by circuit simulations, show that RTD design improvements (lower reverse leakage, higher breakdown voltage) significantly boost EH performance and, together with accurate EH modelling, yield substantial gains in the rate-power region for THz SWIPT, while simple baseline models fail to capture RTD non-monotonic behavior.

Abstract

In this paper, we study THz simultaneous wireless information and power transfer (SWIPT) systems. Since coherent information detection is challenging at THz frequencies and Schottky diodes may not be efficient for THz energy harvesting (EH) and information detection, we employ unipolar amplitude shift keying (ASK) modulation at the transmitter (TX) and a resonant tunnelling diode (RTD)-based EH circuit at the receiver (RX) to extract both information and power from the RX signal. We model the dependence of the instantaneous output power at the RX on the instantaneous received power by a non-linear piecewise function, whose parameters are adjusted to fit circuit simulation results. To determine the rate-power tradeoff in THz SWIPT systems, we derive the distribution of the TX signal that maximizes the mutual information between the TX and RX signals subject to constraints on the required average harvested power at the RX and the peak signal amplitude at the TX. Since the computational complexity of maximizing the mutual information may be too high for real-time THz SWIPT systems, for high and low required average harvested powers, we also obtain the suboptimal input signal distribution that maximizes the achievable information rate numerically and in closed form, respectively. Furthermore, based on the obtained results, we propose a suboptimal closed-form TX distribution which also achieves a desired harvested power at the RX. Our simulation results show that a lower reverse current flow and a higher breakdown voltage of the employed RTD are preferable when the input signal power at the RX is low and high, respectively. Finally, we demonstrate that for low and high received signal powers, the rate-power tradeoff of THz SWIPT systems is determined by the peak amplitude of the TX signal and the maximum instantaneous harvested power, respectively.

Figures (10)

• Figure 1: THz SWIPT system model employing a TX with a highly directive antenna and a single-antenna RX equipped with an rtd-based rectifying circuit.
• Figure 2: I-V characteristic of the Keysight ADS RTD design in Clochiatti2022 matched to the measurement data in Clochiatti2022, and I-V characteristics of two improved RTD designs with higher breakdown voltage $U_\text{br}$ and lower reverse leakage current $I_\text{rev}$, respectively.
• Figure 3: Proposed EH model in (\ref{['Eqn:EHmodel']}) with $N = 5$ monotonic functions $\varphi_n(\cdot)$.
• Figure 4: Equivalent EH model for the solution of (\ref{['Eqn:GeneralOptimizationProblem']}).
• Figure 5: The pdfs $f_x^\text{ach}$ of $x$ in (\ref{['Eqn:UniformDistributionX']}) and (\ref{['Eqn:PdfxAchievable']}) and proposed closed-form pdfs $f_x^\text{cf}(x)$ in (\ref{['Eqn:ClosedFormPdfX']}) for different power ratios $\frac{\bar{P}_\text{req}}{\bar{P}_\text{max}}$.

Theorems & Definitions (16)

• Proposition 1
• proof
• Proposition 2
• proof
• Lemma 1
• proof
• Proposition 3
• proof
• Corollary 1
• proof