Wireless Energy Transfer in Extra-Large Massive MIMO Rician Channels
Abstract : In application scenarios such as Internet of Things, a large number of energy receivers (ERs) exist and line-of-sight (LOS) propagation could be common. Considering this, we investigate wireless energy transfer (WET) in extra-large massive MIMO Rician channels. We derive analytical expressions of the received net energy for different schemes, including 1) training-based WET, where the ER sends beacon signal for channel training and the energy transmitter (ET) uses the channel estimate for energy beamforming, 2) LOS beamforming, where the ET transmits to the LOS direction of the ER, and 3) energy harvesting, which allows an ER to harvest the training energy from the other ERs. We derive a path loss threshold for switching between training and LOS beamforming-based WET. We further show that the WET scheme selection of one ER is not affected by the other ERs, and the energy harvested from training is minimal in practice. With these insights, we propose an algorithm for the multi-ER scenario, which minimizes the power consumption by iteratively updating the WET scheme selection and power allocation for all ERs. Simulations show that the proposed algorithm achieves near-optimal performance as compared to exhaustive searching, while with much lower implementation complexity.
? In contrast to most existing works in the literature, we focus on ascertaining whether the use of large antenna arrays could substantially extend the feasible range of WET while maintaining the receive power level in the same order such that a reasonable rectenna efficiency can be maintained.
? A rich literature modeling the EH circuits exists, and it has been known that different types of RF-DC conversion circuits lead to different optimal waveforms.
? The same linear increase of the mean sum-power also exists when using a precoder with access to instantaneous full-CSIT.
? In this paper, we aim to fill in this gap by investigating the impact of hardware impairments on the achievable rate of regular and LS-MIMO systems over Rician fading channels.
? Some researchers have analyzed the impact of transceiver hardware impairments on MIMO system performance.
? Therefore, it is important to analyze the impact of transceiver hardware impairments on the performance of MIMO systems to provide useful guidance for practical systems design.
? Moreover, the impact of the Rician K-factor and hardware impairments on the achievable rate performance are investigated.
• The precoders proposed in the present paper are based on statistical CSIT (mean and correlation) and attain power gains very close to the optimal precoder with instantaneous fullCSIT available at the BS.
• To assess the proposed precoding techniques, this paper adopts one model that still mimics important features such as the sensitivity and saturation phenomena.
• The advantage of the proposed precoding scheme stands out in comparison with the energy harvesting ability of both the SA and AA schemes.
• To withstand that effect, a constrained optimization of the precoders is proposed which, besides naturally enforcing inter-cluster fairness, can also conform the power domain at the terminals’ antennas to the linear domain of their non-linear EH circuit.
? In LS-MIMO systems, each base station is equipped with a large number of antennas to improve the spectral and energy efficiency.
? Moreover, reveals that the residual hardware impairments dominate on the achievable rate performance of MIMO systems in the high-SNR regime.
? However, we show that the non-ideal LS-MIMO system can still achieve high spectra l efficiency due to its huge degrees of freedom.
? By employing multiple antennas at the transceiver, wireles s systems can significantly increase the spectral efficiency and transmission reliability.
? It is very attractive to deploy LS antenna elements with cheap, compact and power-efficient radio and digital-processing hardware.
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