IEEE Journal on Selected Areas in Communications · 2015 · 162 citations · 30 references
EngineeringCommunicationElectrical EngineeringAntennasOptimizationWireless CommunicationsBeamformingChannel EstimationEnergy EfficiencyWireless Channel ModelingWireless NetworksWireless Power TransferBeam Energy OptimizationChannel State InformationEnergy AllocationEnergy BeamformingEnergy-efficient CommunicationMulti-receiver SystemsRfid TagsTransmit Beamforming
Acquiring forward‑channel state information (F‑CSI) at the energy transmitter in backscatter systems is difficult because tags lack the energy and hardware to estimate or feed back the channel. This work investigates RF‑enabled wireless energy transfer via energy beamforming from a multi‑antenna transmitter to multiple receivers in an RFID‑style backscatter communication system. The transmitter estimates backscatter‑channel state information (BS‑CSI) from observed backscatter signals, analyzes the resulting harvested energy, and optimizes resource allocation—including channel‑training energy, beam weights, and a block‑coordinate‑descent algorithm for proportional‑fair energy maximization—to maximize total harvested energy. We show that optimal channel‑training energy can be derived in closed form for a single receiver, that a single‑beam weighted‑sum‑energy scheme is optimal yet unfair, motivating a proportional‑fair approach solved by a biconvex block‑coordinate‑descent algorithm, and that the optimized solutions achieve harvested energy within 10 % of the perfect‑CSI benchmark.
We study RF-enabled wireless energy transfer (WET) via energy beamforming, from a multi-antenna energy transmitter (ET) to multiple energy receivers (ERs) in a backscatter communication system such as RFID. The acquisition of the forward-channel (i.e., ET-to-ER) state information (F-CSI) at the ET (or RFID reader) is challenging, since the ERs (or RFID tags) are typically too energy-and-hardware-constrained to estimate or feedback the F-CSI. The ET leverages its observed backscatter signals to estimate the backscatter-channel (i.e., ET-to-ER-to-ET) state information (BS-CSI) directly. We first analyze the harvested energy obtained using the estimated BS-CSI. Furthermore, we optimize the resource allocation to maximize the total utility of harvested energy. For WET to single ER, we obtain the optimal channel-training energy in a semiclosed form. For WET to multiple ERs, we optimize the channel-training energy and the energy allocation weights for different energy beams. For the straightforward weighted-sum-energy (WSE) maximization, the optimal WET scheme is shown to use only one energy beam, which leads to unfairness among ERs and motivates us to consider the complicated proportional-fair-energy (PFE) maximization. For PFE maximization, we show that it is a biconvex problem, and propose a block-coordinate-descent-based algorithm to find the close-to-optimal solution. Numerical results show that with the optimized solutions, the harvested energy suffers slight reduction of less than 10%, compared to that obtained using the perfect F-CSI.
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Handbook of Mathematical Functions
Milton Abramowitz, I. A. Stegun · 1972 · 15.4K citations
Charging and rate control for elastic traffic
F. P. Kelly · European Transactions on Telecommunications · 1997 · 3K citations · Full text