Energy-Efficient Power Allocation in OFDM Systems with Wireless Information and Power Transfer

This paper considers an orthogonal frequency division multiplexing (OFDM) downlink point-to-point system with simultaneous wireless information and power transfer. It is assumed that the receiver is able to harvest energy from noise, interference, and the desired signals. We study the design of power allocation algorithms maximizing the energy efficiency of data transmission (bit/Joule delivered to the receiver). In particular, the algorithm design is formulated as a high-dimensional non-convex optimization problem which takes into account the circuit power consumption, the minimum required data rate, and a constraint on the minimum power delivered to the receiver. Subsequently, by exploiting the properties of nonlinear fractional programming, the considered non-convex optimization problem, whose objective function is in fractional form, is transformed into an equivalent optimization problem having an objective function in subtractive form, which enables the derivation of an efficient iterative power allocation algorithm. In each iteration, the optimal power allocation solution is derived based on dual decomposition and a one-dimensional search. Simulation results illustrate that the proposed iterative power allocation algorithm converges to the optimal solution, and unveil the trade-off between energy efficiency, system capacity, and wireless power transfer: (1) In the low transmit power regime, maximizing the system capacity may maximize the energy efficiency. (2) Wireless power transfer can enhance the energy efficiency, especially in the interference limited regime.Comment: 6 pages, Accepted for presentation at the IEEE International Conference on Communications (ICC) 201

Wireless Power Transfer for High-precision Position Detection of Railroad Vehicles

Detection of vehicle position is critical for successful operation of intelligent transportation system. In case of railroad transportation systems, position information of railroad vehicles can be detected by GPS, track circuits, and so on. In this paper, position detection based on tags onto sleepers of the track is investigated. Position information stored in the tags is read by a reader placed at the bottom of running railroad vehicle. Due to limited capacity of battery or its alternative in the tags, power required for transmission of position information to the reader is harvested by the tags from the power wirelessly transferred from the reader. Basic mechanism in wireless power transfer is magnetic induction and power transfer efficiency according to the relative location of the reader to a tag is discussed with simulation results. Since power transfer efficiency is significantly affected by the ferromagnetic material (steel) at the bottom of the railroad vehicle and the track, magnetic beam shaping by ferrite material is carried out. With the ferrite material for magnetic beam shaping, degradation of power transfer efficiency due to the steel is substantially reduced. Based on the experimental results, successful wireless power transfer to the tag coil is possible when transmitted power from the reader coil is close to a few watts.Comment: 2015 IEEE Power, Communication and Information Technology Conference (PCITC) accepted, preprinte

Beamforming for Magnetic Induction based Wireless Power Transfer Systems with Multiple Receivers

Magnetic induction (MI) based communication and power transfer systems have gained an increased attention in the recent years. Typical applications for these systems lie in the area of wireless charging, near-field communication, and wireless sensor networks. For an optimal system performance, the power efficiency needs to be maximized. Typically, this optimization refers to the impedance matching and tracking of the split-frequencies. However, an important role of magnitude and phase of the input signal has been mostly overlooked. Especially for the wireless power transfer systems with multiple transmitter coils, the optimization of the transmit signals can dramatically improve the power efficiency. In this work, we propose an iterative algorithm for the optimization of the transmit signals for a transmitter with three orthogonal coils and multiple single coil receivers. The proposed scheme significantly outperforms the traditional baseline algorithms in terms of power efficiency.Comment: This paper has been accepted for presentation at IEEE GLOBECOM 2015. It has 7 pages and 5 figure

Analytical simulation of SPS system performance, volume 3, phase 3

The simulation model for the Solar Power Satellite spaceantenna and the associated system imperfections are described. Overall power transfer efficiency, the key performance issue, is discussed as a function of the system imperfections. Other system performance measures discussed include average power pattern, mean beam gain reduction, and pointing error