Information Harvesting for Far-Field RF Power Transfer through Index Modulation

Abstract

In today's smart world, Internet of Things (IoT) offers a very large scale of technologies and use-cases. An IoT system is comprised of a huge amount of low-power IoT network elements, sensors, and smart devices, connected with each other. For these devices, it is important to have a sufficient level of energy resource for communication and to receive software/firmware updates periodically. In this aspect, wireless power transfer is a popular paradigm to tackle energy limitations. Therein, the battery of IoT devices can be remotely replenished by means of radio-frequency (RF) radiated signaling, referred to as far-field wireless power transfer. Furthermore, harvesting energy from ambient communication signals available in the environment introduces simultaneous wireless information and power transfer technology. These systems face the trade-off between information capacity and energy harvesting efficiency. Accordingly, various signaling design frameworks have been proposed to comply with different system preferences between power and information. In this work, aside from existing trends, we propose a novel concept, Information Harvesting (IH), which introduces a novel protocol that lies in transmitting information on top of the existing wireless power transfer mechanism. Considering the diversity of IoT networks and the availability of wireless power transfer infrastructure, the proposed Information Harvesting principle may turn out to be a pivotal methodology that combines physical layer security with wireless power transfer particularly for the cases where a large number of IoT devices require the software/firmware updates along with periodical battery recharging needs.

A New Information Harvesting Mechanism for Far-Field Wireless Power Transfer

“…In this section, we would like to investigate the advantages of implementing information seeding mechanism which results from QSM-based IH implementation compared with GSSK-based IH implementation given in [14]. For this purpose, the average harvested power at the EH, the secrecy rates at the IR and bit error rate at IR are used as the performance indicators.…”

“…Note that the channel between the WPT and the IR relies on QSM-based GSSK modulated antenna indices so the capacity analysis deducts into a capacity analysis for discrete-input continuous-output memoryless channel (DCMC) [22] and it might be not straightforward to obtain the closed-form analysis in most cases. With the existence of Eve in the service area, the secrecy rate of IH can be expressed as [21] R IH = max{0, I IR (y IR , h l,eff ) − I eve y eve , g l,eff }, (14) Note that positive secrecy from ( 14) implies communication opportunity on top of existing WPT mechanism even some information can be leaked to Eve in the service area.…”

“…From this aspect, the PAPR values of GSSK-based IH in [14] and the proposed IH with respect to different N a values when the dominant LoS exists are illustrated in Fig. 2.…”

“…Herein, the calculation of the AER lies on comparing transmit antenna array vector and estimated antenna array vector at IR and Eve. The simulated secrecy rates of the QSM-based IH mechanism and IH mechanism given in [14] with respect to N a are given in Fig. 4.…”

“…In principle, the IH framework consists of two cycles where information seeding cycle aims to embed the information bits into WPT waveform without any termination or disturbance in existing harvesting activity and information harvesting cycle refers to sense the variations occurred in information seeding cycle at intended receivers. The generalized space shift keying (GSSK)-based IH mechanism and its performance in terms of secrecy capacity and average harvested power was investigated in [14].…”