SWIPT Signalling over Complex AWGN Channels with Two Nonlinear Energy Harvester Models

TL;DR

This paper analyzes the capacity of complex AWGN channels with nonlinear energy harvesters in SWIPT systems, revealing optimal input distributions and the impact of various constraints on capacity.

Contribution

It introduces a comprehensive capacity analysis considering two nonlinear energy harvester models and multiple constraints, highlighting the discreteness of optimal inputs.

Findings

Capacity under AP and RDP constraints equals that under AP alone.

Optimal input amplitude is discrete with finite mass points.

Capacity can be approached arbitrarily under certain constraints.

Abstract

Simultaneous Wireless Information and Power Transfer (SWIPT) is subject to nonlinearity at the energy harvester that leads to significant changes to transmit signal designs compared to conventional wireless communications. In this paper, the capacity of a discrete time, memoryless and complex Additive White Gaussian Noise (AWGN) channel in the presence of a nonlinear energy harvester at the receiver is studied. Considering the two common nonlinear energy harvester models introduced in the literature, two sets of constraints are considered. First the capacity is studied under average power (AP), peak amplitude (PA) and receiver delivery power (RDP) constraints. The RDP constraint is modelled as a linear combination of even-moment statistics of the channel input being larger than a threshold. It is shown that the capacity of an AWGN channel under AP and RDP constraints is the same as the capacity of an AWGN channel under an AP constraint, however, depending on the two constraints, it can be either achieved or arbitrarily approached. It is also shown that under AP, PA and RDP constraints, the amplitude of the optimal inputs is discrete with a finite number of mass points. Next, the capacity is studied under AP, PA and output outage probability (OOP) constraints. OOP is modelled as satisfying a certain probability inequality for the amplitude of the received signal being outside of a given interval. Similarly, it is shown that the amplitude of the optimal input is discrete with a finite number of mass points.