On the Capacity of SWIPT Systems with a Nonlinear Energy Harvesting Circuit

Abstract

In this paper, we study information-theoretic limits for simultaneous wireless information and power transfer (SWIPT) systems employing a practical nonlinear radio frequency (RF) energy harvesting (EH) receiver. In particular, we consider a three-node system with one transmitter that broadcasts a common signal to separated information decoding (ID) and EH receivers. Owing to the nonlinearity of the EH receiver circuit, the efficiency of wireless power transfer depends significantly on the waveform of the transmitted signal. In this paper, we aim to answer the following fundamental question: What is the optimal input distribution of the transmit waveform that maximizes the rate of the ID receiver for a given required harvested power at the EH receiver? In particular, we study the capacity of a SWIPT system impaired by additive white Gaussian noise (AWGN) under average-power (AP) and peak-power (PP) constraints at the transmitter and an EH constraint at the EH receiver. Using Hermite polynomial bases, we prove that the optimal capacityachieving input distribution that maximizes the rate-energy region is unique and discrete with a finite number of mass points. Furthermore, we show that the optimal input distribution for the same problem without PP constraint is discrete whenever the EH constraint is active and continuous zero-mean Gaussian, otherwise. Our numerical results show that the rate-energy region is enlarged for a larger PP constraint and that the rate loss of the considered SWIPT system compared to the AWGN channel without EH receiver is reduced by increasing the AP budget.

A Learning Approach to Wireless Information and Power Transfer Signal and System Design

“…The delivery power Pdel harvested at the receiver is modelled as in (8). We recall that for the power delivery purposes, the received RF signal is directly fed to the EH.…”

“…Adopting rectenna nonlinear model of 4 [3,8,18], the received RF signal yRF(t) is converted at the rectifier's output into a DC signal across a load resistance RL. Assuming perfect impedance matching, i.e., Rin = Ra (Rin is the equivalent input impedance of the circuit observed after the antenna), the received power is completely transferred to the rectifier.…”

“…The antenna is modelled as a voltage source followed by a resistance and the rectifier is modelled as a nonlinear diode followed by low pass filter (LPF) 5. We note that the nonlinear model presented in this paper is a generalization of the nonlinear model to complex channel inputs introduced in[18,8].…”

Conditional Capacity and Transmit Signal Design for SWIPT Systems With Multiple Nonlinear Energy Harvesting Receivers

“…To specify the EH constraints, we employ the harvested DC power function derived for our newly developed nonlinear EH saturation model. In addition, we impose average-power (AP) and peak-power (PP) constraints at the power transmitter 1 . We note that, for a linear EH model, the considered problem is trivial since, in this case, the harvested DC power depends only on the average input RF power, which renders the input distribution of the transmit symbols irrelevant for WPT.…”

“…The discreteness and finiteness of optimal input distributions for other channels have been reported in [22], [23], [25]- [27]. • Different from our preliminary work in [1], in this paper, we additionally consider the following: -In order to accurately model the harvested DC power, we take into account not only the forward but also the reverse breakdown I-V characteristic of the rectifying diode. Consequently, the proposed nonlinear EH model captures the saturation behaviour of the output DC power at high input RF powers.…”