Secure RF Energy Harvesting Scheme for Future Wireless Networks
Authors: Arachchilage Dushantha Nalin K. Jayakody , Jameel Furqan , Qaraqe Marwa 
Published: June 2019

Wireless communication is shaping the future of seamless and reliable connectivity of billions of devices. The communication sector in Qatar is mainly driven by rising demand of higher data rates and uninterrupted connectivity of wireless devices. Wireless fidelity (Wi-Fi), cellular telephone and computer interface devices (e.g. Bluetooth) are a few of the commonly used applications for wireless distribution of information in Qatar. According to analysts, strong growth of Islamic banking, increase in IT consolidation and increased adoption of mobility solutions are some of the key contributors to the growth of digital infrastructure in Qatar. Modernization of legacy infrastructure is another focal point of government of Qatar to enable e-government initiative in rural areas and Tier II/ III cities of Qatar which has long term effects in various domains such as health, electricity, water, heat, communication and trade. Considering this exponential rise of wireless communication in Qatar, a great deal of research is being done from the perspective of secure deployment of new wireless networks. There is also a growing demand to develop more energy-efficient communication techniques to reduce the consumption of fossil fuel without compromising the quality of experience of users. This is also beneficial for solving economic issues that cellular operators are faced with the ever growing number of users. Moreover, with the upcoming FIFA world cup in 2022, millions of dollars are being spent to enhance the capacity and security of existing and upcoming communication networks. However, with greater connectivity and ultimate functionality come several important challenges. The first challenge is the security of data or more specifically who has access to the data. The broadcast nature of wireless channels implies that the transmitted information signals are also received by nodes other than the intended receiver, which results in the leakage of information. Encryption techniques at higher layers are used to secure transmitted information. However, the high computational complexity of these cryptographic techniques consumes significant amount of energy. Moreover, secure secret key management and distribution via an authenticated third party is typically required for these techniques, which may not be realizable in a dense wireless networks. Therefore, a considerable amount of work has recently been devoted to information-theoretic physical layer security (PLS) as a secure communication technique which exploits the characteristics of wireless channels, such as fading, noise, and interferences. The varying nature of these factors causes randomness in the wireless channel which can be exploited to achieve security. The transmission of secret messages takes place when the receiver»s channel experiences less fading than the eavesdropper»s channel, otherwise transmission remains suspended. The second concern is regarding the limited lifetime of wireless devices, especially when massive amount of data needs to be collected and transferred across the network. This challenge can be addressed by innovative means of powering, and for small energy limited devices, this implies the use of energy harvesting (EH) techniques. In this context, the transfer of data and power over a common electromagnetic (EM) wave has gained significant research interest over the past decade. The technique which merges wireless information transfer (WIT) with wireless power transmission (WPT) is commonly termed as simultaneous wireless information and power transfer (SWIPT). However, SWIPT systems cannot be supported using conventional design of transmitter and receiver. To address this issue, two broad categories of receiver architectures have been proposed in SWIPT literature i.e. separated and integrated architecture. In separated receiver architecture, the information decoder and energy harvester act as dedicated and separate units. This although not only increases the cost of receiver but also increases the complexity of the hardware. In contrast, the integrated receiver architecture jointly processes the information and energy using a unified circuitry for both. This architecture reduces the cost and hardware complexity Our work attempts to address the aforementioned issues by evaluating secrecy performance and proposing practical secrecy enhancement scheme in EH wireless devices. In particular, we investigate PLS in SWIPT systems in the presence of multiple eavesdroppers. The secrecy performance of the SWIPT system is analyzed for Rician faded communication links. The security performance is analyzed for imperfect channel estimation, and both separated and integrated receiver architectures for the SWIPT system. We derive closed-form expressions of the secrecy outage probability and the ergodic secrecy rate for the considered scenario and validate the derived analytical expressions through extensive simulations. Our results reveal that an error floor appears due to channel estimation errors at high values of signal to noise ratio (SNR); such that outage probability cannot be further minimized despite an increase in the SNR of the main link. Moreover, the results show that largest secrecy rate can be achieved when the legitimate receiver is equipped with separated SWIPT receiver architecture and the eavesdroppers have an integrated SWIPT receiver architecture. It is also demonstrated that the power splitting factor at both legitimate receiver and at eavesdroppers play a prominent role in determining the secrecy performance of SWIPT. We prove that a larger power splitting factor is required to ensure link security for poor channel estimation. Finally, our work discusses transmit antenna selection and baseline antenna selection schemes to improve security. Therein, it is shown that transmit antenna selection outperforms baseline antenna selection. The results provided in this work can be readily used to evaluate the secrecy performance of SWIPT systems operating in the presence of multiple eavesdroppers.