System Design and Performance Study for Wireless Information and Energy Transfer in the Internet of Things
In a tremendous evolution, billions of physical objects are being connected to the Internet, shaping Internet of Things (IoT) as one of the most disruptive technologies that has ever been witnessed. This revolutionary technology, however, encounters the key challenge of sustainability. Wireless information and energy transfer (WIET) has emerged as a promising solution to overcome this significant challenge. This thesis focuses on developing WIET with respect to the realistic applications and enhancing the system performance through devising effective signal processing methods and novel system designs. We study point-to-point WIET systems with bidirectional communication. Multiple-input multiple-output (MIMO) with antenna switching (AS) and beamforming are investigated to improve the achieved downlink-uplink rate region in such systems. An optimal and a low-complexity algorithm are proposed to solve the problem of joint optimization of AS and beamforming. It is shown that the computational complexity can be substantially alleviated and also a near-optimal performance can be obtained by the proposed low-complexity algorithm. Moreover, we investigate the orthogonal and non-orthogonal multiple access (OMA and NOMA) in the downlink WIET systems. The analytical results show that OMA can achieve a larger rate region than NOMA when the channel power gains of users are not sufficiently different. Also, we show that cognitive-radio-inspired NOMA (CR-NOMA) as an important variation of NOMA can outperform OMA only if the channel power gains of users are sufficiently different and the target rate of the weak user is above a threshold. Finally, we propose novel coordinated multi-point NOMA (CoMP-NOMA) schemes, namely joint transmission NOMA (JT-NOMA) and Alamouti NOMA (A-NOMA), to combat the key challenge of inter-cell interference (ICI) in the multicell WIET networks. We show that A-NOMA can achieve a larger outage rate region than JT-NOMA and joint transmission OMA (JT-OMA) in high signal-to-noise ratio. A particularly interesting observation is that when the difference between the expectations of effective channel power gains is not sufficiently large, JT-OMA performs better than JT-NOMA. This dissertation contributes to transforming WIET form a potential solution into an enabling technology which can significantly improve the spectral efficiency and sustainability in wireless networks and IoT systems.