Broadly speaking, there are two research directions based on the usage of harvested energy as shown in the figure: “simultaneous wireless information and power transfer (SWIPT)”, where the access point (AP) broadcasts both information and energy signals to user terminals in the downlink, and user terminals then use the harvested energy to decode information; “wireless powered communication network (WPCN)”, where the AP first broadcasts energy signals to user terminals in the downlink, and then user terminals transmit their information to AP in the uplink using their harvested energy.

For both SWIPT and WPCN, the dual use of RF signals for both information and energy transmissions encounters many new research problems and implementation issues that need to be carefully addressed. For example, the current commercial receiver circuit cannot decode the information and harvest the energy from the same RF signal at the same time. Moreover, current protocols for wireless communications only support battery-charged devices, and thus new system-level protocols are needed to schedule the energy transmission and information transmission in a WPCN.

During my Ph.D. study, I have conducted a lot of pioneering works on the RF-based wireless energy harvesting technique. Our proposed receiver architecture for SWIPT and system-level protocol for WPCN are widely adopted in the relevant area, which is evidenced by the large number of citations of many papers. Our aim is to open up the potential to build a network with larger throughput, higher robustness, and increased flexibility compared to its battery-powered counterpart.

Journal Publications:

1. L. Liu, R. Zhang, and K. C. Chua, “Wireless information transfer with opportunistic energy harvesting,” IEEE Trans. Wireless Commun., vol. 12, no. 1, pp. 288-300, Jan. 2013. ESI Highly Cited Paper (data from Web of Science on June 18 2017)
2. L. Liu, R. Zhang, and K. C. Chua, “Wireless information and power transfer: a dynamic power splitting approach,” IEEE Trans. Commun., vol. 61, no. 9, pp. 3990-4001, Sep. 2013. ESI Highly Cited Paper (data from Web of Science on June 18 2017)
3. L. Liu, R. Zhang, and K. C. Chua, “Secrecy wireless information and power transfer with MISO beamforming,” IEEE Trans. Signal Process., vol. 62, no. 7, pp. 1850-1863, Apr. 2014. ESI Highly Cited Paper (data from Web of Science on June 18 2017)
4. Q. Shi, L. Liu, W. Xu, and R. Zhang, “Joint transmit beamforming and receive power splitting for MISO SWIPT systems,” IEEE Trans. Wireless Commun., vol. 13, no. 6, pp. 3269-3280, June, 2014. ESI Highly Cited Paper (data from Web of Science on June 18 2017)
5. J. Xu, L. Liu, and R. Zhang, “Multiuser MISO beamforming for simultaneous wireless information and power transfer,” IEEE Trans. Signal Process., vol. 12, no. 8, pp. 4798-4810, Aug. 2014. ESI Highly Cited Paper (data from Web of Science on June 18 2017)
6. L. Liu, R. Zhang, and K. C. Chua, “Multi-antenna wireless powered communication with energy beamforming,” IEEE Trans. Commun., vol. 62, no. 12, pp. 4349-4361, Dec. 2014. ESI Highly Cited Paper (data from Web of Science on June 18 2017)
7. S. Lee, L. Liu, and R. Zhang, “Collaborative wireless energy and information transfer in interference channel,” IEEE Trans. Wireless Commun., vol. 14, no. 1, pp. 545-557, Jan. 2015. ESI Highly Cited Paper (data from Web of Science on June 18 2017)
8. H. Xing, L. Liu, and R. Zhang, “Secrecy wireless information and power transfer in fading wiretap channel,” IEEE Trans. Veh. Technol., vol. 65, no. 1, pp. 180-190, Jan. 2016. ESI Highly Cited Paper (data from Web of Science on June 18 2017)

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