SWIPT with practical modulation and RF energy harvesting sensitivity

In this paper, we investigate the performance of simultaneous wireless information and power transfer (SWIPT) in a point-to-point system, adopting practical M-ary modulation. We take into account the fact that the receiver’s radio-frequency (RF) energy harvesting circuit can only harvest energy when the received signal power is greater than a certain sensitivity level. For both power-splitting (PS) and time-switching (TS) schemes, we derive the energy harvesting performance as well as the information decoding performance for the Nakagamim fading channel. We also analyze the performance tradeoff between energy harvesting and information decoding by studying an optimization problem, which maximizes the information decoding performance and satisfies a constraint on the minimum harvested energy. Our analysis shows that (i) for the PS scheme, modulations with high peak-to-average power ratio achieve better energy harvesting performance, (ii) for the TS scheme, it is desirable to concentrate the power for wireless power transfer in order to minimize the non-harvested energy caused by the RF energy harvesting sensitivity level, and (iii) channel fading is beneficial for energy harvesting in both PS and TS schemes.ARC Discovery Projects Grant DP14010113

Energy Harvesting Wireless Sensor Networks: Delay Analysis Considering Energy Costs of Sensing and Transmission

Energy harvesting (EH) provides a means of greatly enhancing the lifetime of wireless sensor nodes. However, the randomness inherent in the EH process may cause significant delay for performing sensing operation and transmitting the sensed information to the sink. Unlike most existing studies on the delay performance of EH sensor networks, where only the energy consumption of transmission is considered, we consider the energy costs of both sensing and transmission. Specifically, we consider an EH sensor that monitors some status environmental property and adopts a harvest-then-use protocol to perform sensing and transmission. To comprehensively study the delay performance, we consider two complementary metrics and analytically derive their statistics: (i) update age - measuring the time taken from when information is obtained by the sensor to when the sensed information is successfully transmitted to the sink, i.e., how timely the updated information at the sink is, and (ii) update cycle - measuring the time duration between two consecutive successful transmissions, i.e., how frequently the information at the sink is updated. Our results show that the consideration of sensing energy cost leads to an important tradeoff between the two metrics: more frequent updates result in less timely information available at the sink.Comment: submitted for possible journal publicatio

Wireless Communication Networks Powered by Energy Harvesting

This thesis focuses on the design, analysis and optimization of various energy-constrained wireless communication systems powered by energy harvesting (EH). In particular, we consider ambient EH wireless sensor networks, wireless power transfer (WPT) assisted secure communication network, simultaneous wireless information and power transfer (SWIPT) systems, and WPT-based backscatter communication (BackCom) systems. First, we study the delay issue in ambient EH wireless sensor network for status monitoring application scenarios. Unlike most existing studies on the delay performance of EH sensor networks that only consider the energy consumption of transmission, we consider the energy costs of both sensing and transmission. To comprehensively study the delay performance, we consider two complementary metrics and analyze their statistics: (i) update age - measuring how timely the updated information at the sink is, and (ii) update cycle - measuring how frequently the information at the sink is updated. We show that the consideration of sensing energy cost leads to an important tradeoff between the two metrics: more frequent updates result in less timely information available at the sink. Second, we study WPT-assisted secure communication network. Specifically, we propose to use a wireless-powered friendly jammer to enable low-complexity secure communication between a source node and a destination node, in the presence of an eavesdropper. We propose a WPT-assisted secure communication protocol, and analytically characterize its long-term behavior. We further optimize the encoding-rate parameters for maximizing the throughput subject to a secrecy outage probability constraint. We show that the throughput performance differs fundamentally between the single-antenna jammer case and the multi-antenna jammer case. Third, exploiting the fact that the radio-frequency (RF) signal can carry both information and energy, we study a point-to-point simultaneous wireless information and power transfer (SWIPT) system adopting practical M-ary modulation for both the power-splitting (PS) and the time-switching (TS) receiver architectures. Unlike most existing studies, we take into account the receiver’s sensitivity level of the RF-EH circuit. We show several interesting results, such as for the PS scheme, modulations with high peak-to-average power ratio achieve better EH performance. Then, inspired by the PS-based SWIPT receiver, we propose a novel information receiver, which involves joint processing of coherently and non-coherently received signals, and hence, creates a three-dimensional received signal space. We show that the achievable rate of a splitting receiver provides a 50% rate gain compared to either the conventional coherent or non-coherent receiver in the high SNR regime. Last, we propose the design of WPT-based full-duplex backscatter communication (BackCom) networks for energy-constrained Internet-of-Things applications, where a novel multiple-access scheme based on time-hopping spread-spectrum (TH-SS) is designed to enable both one-way power transfer and two-way information transmission in coexisting backscatter reader-tag links. Comprehensive performance analysis of BackCom networks is presented. We show some interesting design insights, such as: a longer TH-SS sequence reduces the bit error rates (BERs) of the two-way information transmission but results in lower energy-harvesting rate at the tag; a larger number of BackCom links improves the energy-harvesting rate at the tags but also increase the BERs for the information transmission