Abstract
As an emerging paradigm, supplying power by radio frequency signal has been a key technology for the wireless powered communication network (WPCN) to prolong the lifetime. This paper considers a multiple input multiple output (MIMO) system where users are charged only by one source. The source is equipped with multiple antennas while each user with one antenna. Besides receiving information as the traditional way, the source has the capacity to transfer energy with beamforming, which can be harvested by users to store for information transmission in the later. However, the unknown channel state information (CSI), low energy efficiency, and various demands of transmitting volume jointly raise inaccurate, wasteful, and flexible conditions in transmitting design. On the other hand, energy and spectrum efficient solutions are indispensable to the success of Internet of Things (IoT). In this case, we put forward a novel design of downlink energy transfer, uplink information transmission, and channel estimation to achieve a practical efficient transmission. By jointly optimizing the source antenna number, power allocation, energy beamforming vectors, and each phase time of channel estimation, energy harvest, and information transmission, we aim to achieve the optimized system energy efficiency with constraints of signal-to-noise ratio (SNR), data transmission volume, and transmitting power. Based on fractional programming and Lagrangian dual functions, we also put forward a distributed iterative algorithm to solve the formulated problem optimally. Simulation results verify the convergence of our proposed algorithm and illustrate the relationship between variables of antenna number, data volume requirement, pathloss factor and system performance of sum-throughput, energy efficiency, and user fairness. Our proposed transmitting design can achieve the optimized energy efficiency, whose upper bound is improved by appropriate massive antenna employment.
Highlights
In recent years, the Internet of Things (IoT) is emerging as an important networking paradigm which enables communication among physical objects [1,2,3]
We study energy efficiency of a downlink energy transfer and uplink information transmission in the multiuser multiple input multiple output (MIMO) system with imperfect channel state information (CSI)
In the general trend, the less energy is reserved for the test phase in three cases, the more power is obtained by users in the energy harvesting phase
Summary
The Internet of Things (IoT) is emerging as an important networking paradigm which enables communication among physical objects [1,2,3]. Artificial intelligence (AI) management technologies adopting dynamic methods to control for IoT in smart cities are needed more and more. Long distance wireless energy transfer (WET) has been studied as a potential technology to solve the lifetime problem of the wireless powered communication system [4]. Users can be supplied by radio frequency (RF) signal to prolong the lifetime. It has been proved that a user equipped with proper circuit can receive signal and convert it into energy to store. When transmission frequency is 915 Hz, it is reported that 3.5 mW and 1uW can be harvested from RF signal with distances of 0.6 m and 1.1 m, respectively [5]
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