Abstract
In multi-antenna simultaneous wireless information and power transfer (SWIPT) system, beamforming strategy has been widely analyzed due to the increasing signal strength. It can not only increase the signal strength in the direction of the antenna array but also reduce the interference strength, which is a good option for SWIPT system to achieve directional transmission of information and energy. However, the traditional beamforming strategy only uses single beamforming vector, and it does not consider the differences between information and energy in SWIPT system. Actually, interference can also be collected as energy. Based on the traditional beamforming strategy, the resources in SWIPT system are not properly utilized. Therefore, this paper proposes a joint beamforming strategy in multi-input and single-output (MISO) SWIPT system. We extend the traditional single beamforming vector into two beamforming vectors to realize independent control of information and energy based on time switching (TS) receiving mode. In information receiving phase, information beamforming vector is used to carry specific user’s information for information alignment. Since there is an orthogonal relationship between information beamforming vector and channel gain vector, we can achieve to eliminate interference and realize error-free information transmission. In energy receiving phase, energy beamforming vector is used to carry user’s energy. Energy beamforming vector and channel gain vector do not require the orthogonality so that the interference can also be collected as energy. In this paper, we model it as a transmission power optimization (TPO) problem, which is a complex non-convex problem. We firstly transform it into a convex problem, and then, it can be solved using CVX toolbox. Simulation results show that the proposed strategy could increase the energy collection at the same transmission power and also decrease the transmission power at the same energy collection.
Highlights
With the development of Internet of Things and communication, low-power sensors are becoming ubiquitous, which increasingly leads to convenient electric charging
By observing the form of the problem in (14), we find that the constraints of the information beamforming vector vk and the energy beamforming vector wk are separated, namely, the value of information beamforming vector vk is irrelevant with the value of energy beamforming vector wk and time switching ratio α
5 Conclusions Traditional beamforming strategy uses the same beamforming vector to align information resources and energy resources, which does not consider the diversity of resources in the simultaneous wireless information and power transfer (SWIPT) system and the utilization of interference
Summary
With the development of Internet of Things and communication, low-power sensors are becoming ubiquitous, which increasingly leads to convenient electric charging. A power line is the most popular way to transmit power for charging the battery [1]. There are obvious limitations for cable charging, such as sensors in the wall and furniture for a smart home or in the body for medical implantation [2, 3]. The wireless charging is a prominent solution to a wide range of applications. In a SWIPT system, there are two kinds of receivers, information receiver (IR) and energy receiver (ER) for information reception and energy collection, respectively. Ma et al EURASIP Journal on Wireless Communications and Networking (2018) 2018:172
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