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In magnetic resonant wireless power transfer (WPT), intermediate resonant coils (i-RCs) can be deployed between a transmitter and a receiver as a means of improving performance, but this entails a high additional cost. In the search for a cost-effective strategy for the use of additional components of WPT, we provide a comparative analysis of the achievable transmission efficiency (TE) between three-coil (3C) and four-coil (4C) systems. In particular, we find optimal control parameters, e.g., load resistance and inductive coupling coefficient, to derive the achievable TE for each system in closed-form expressions. In comparing the achievable TEs of the two systems, we also remark on the effective use of additional coils in two main ways; i) by optimizing the load resistance, the position of the i-RC is determined to be close to the transmitter or the receiver in a 3C system for improving the achievable TE depending on the strength difference between inductive and resonant couplings. Moreover, if the i-RC is placed near the transmitter, the 3C system shows the same achievable TE as the 4C system; ii) by optimizing the inductive coupling coefficient, the achievable TE of the 3C system is not affected by the location of the i-RC, whether it is placed nearer to the transmitter or the receiver, and the 4C system always outperforms the 3C system. Through a series of experiments conducted in a variety of environments, we verify both the validity of these observations and the accuracy of the theoretical analysis.

This article studies simultaneous wireless information and power transfer (SWIPT) for unmanned aerial vehicle (UAV)-enabled Internet-of-Things (IoT) networks. Specifically, it is assumed that a single UAV wishes to simultaneously send common and private data streams as well as energy to multiple IoT nodes, in which the common stream should be recovered by all nodes while private streams are recovered only by the dedicated nodes. In addition, it is assumed that each node uses a power-splitting method that divides the received signal into two parts for energy harvesting and information decoding. Under this setting, by applying a concave–convex procedure (CCCP) method, we propose a novel algorithm that maximizes the minimum rate of private streams of IoT nodes by properly allocating the transmit power of each stream, adjusting the power-splitting ratios at IoT nodes, and designing the trajectory of the UAV, while the common rate and energy harvesting constraints at each node should also be satisfied. Moreover, to enable multiuser communication, a superposition coding in conjunction with successive interference cancellation (SIC) decoding is considered for SWIPT. The performance of the proposed scheme is evaluated and compared with benchmark schemes in various aspects by numerical simulations.

In this article we describe a comparative study of the frequency-selective wireless power transfer (WPT) by considering two different configurations, Tx-Rx-Rx and Rx-Tx-Rx, in a multiple-receiver system. In this system, the receivers have different resonant frequencies and a transmitter can select a driving frequency to transfer power. Using an ECM, we analyze the power transfer efficiency (PTE) and the power distribution according to the variation of the driving frequency. We also find the achievable PTE (η max ) and the maximum power division ratio (α max ) in numerical terms for both configurations. The analysis and experimental results provide insightful information for understanding the effects of the arrangement of the resonators on η max and α max by comparison with the magnetic-resonant WPT, where the resonant frequencies of all the receivers are the same as the driving frequency. We find that the Rx-Tx-Rx configuration is generally more useful for distributing the power to the receivers than the Tx-Rx-Rx configuration, for both frequency-selective and magnetic-resonant WPT. In addition, the frequency-selective WPT enables a more adaptive power distribution than the magneticresonant WPT in the Rx-Tx-Rx configuration while maintaining η max . We further verify that the results of the analysis are in accordance with the measured values, by means of experiments conducted in a variety of environments.

A new interference management scheme based on integer forcing (IF) receivers is studied for the two-user multiple-input and multiple-output (MIMO) interference channel. The proposed scheme employs a message splitting method that divides each data stream into common and private sub-streams, in which the private stream is recovered by the dedicated receiver only while the common stream is required to be recovered by both receivers. Specifically, to enable IF sum decoding at the receiver side, all streams are encoded using the same lattice code. Additionally, the number of common and private streams of each user is carefully determined by considering the number of antennas at transmitters and receivers, the channel matrices, and the effective signal-to-noise ratio (SNR) at each receiver to maximize the achievable rate. Furthermore, we consider various assumptions of channel state information at the transmitter side (CSIT) and propose low-complexity linear transmit beamforming suitable for each CSIT assumption. The achievable sum rate and rate region are analytically derived and extensively evaluated by simulation for various environments, demonstrating that the proposed interference management scheme strictly outperforms the previous benchmark schemes in a wide range of channel parameters due to the gain from IF sum decoding., Comment: Submitted to IEEE Trans. Wireless Commun. (in revision), 31 pages, 6 figures

A new practical multiple-input multiple-output (MIMO) transceiver technique called spatially modulated integer-forcing (SM-IF) is proposed for hybrid beamforming array systems, which combines generalized spatial modulation (GSM) with integer-forcing (IF) MIMO multiplexing transmission to achieve improved spectral efficiency with low system complexity. In the proposed scheme, the transmitter first activates a subset of antennas using analog beamforming and delivers an SM information stream via the index of the activated antenna group. Then MIMO digital multiplexing is applied to send multiple MIMO information streams via multilevel coding (MLC) with binary channel codes through the activated antennas. At the receiver side, the receiver first estimates the index of the activated antenna group to recover the SM stream and then recovers the MIMO streams by IF sum decoding in conjunction with multi-stage decoding. The proposed scheme provides a unified coding framework to achieve a synergistic gain by integrating off-the-shelf practical binary codes and low complexity IF decoding into hybrid beamforming array systems. By extensive link-level numerical simulations, the proposed scheme is shown to outperform both the conventional plain IF MIMO and plain SM approaches. The results demonstrate that the proposed SM-IF can be a promising transceiver technique implementable in practical hybrid beamforming array systems.

The reduction of energy consumption in the reverse osmosis (RO) process is critical. The forward osmosis (FO)-RO hybrid process can be suggested to reduce RO energy consumption. In this study, a numerical FO-RO process model was developed to analyze the FO-RO hybrid process. The performance of the FO-RO hybrid process was compared with the stand-alone RO process. In addition, the impacts of the control parameters for operation, and the intrinsic membrane parameters, were analyzed using sensitivity analysis. In conclusion, the FO-RO hybrid process involves less RO energy consumption than the stand-alone RO process. The FO draw flow velocity and the RO applied pressure were derived as the major factors for controlling the FO-RO process. In addition, the control parameters for operation were found to be more important than the intrinsic membrane parameters in the minimization of RO energy consumption. Subsequently, the FO elements installed in front of the RO process should be configured with a parallel connection, in order to minimize RO energy consumption. The results in this study could be used to develop guidelines for the optimal design of the FO-RO hybrid process.

In this paper, we investigate the optimal configuration of receivers for a three-coil wireless power transfer system in which a transmitter is located between receivers. Based on an equivalent circuit model, we first find the compensatory reactance terms to eliminate cross coupling between receivers. Neglecting cross coupling, we derive an optimal coupling coefficient between a receiver and transmitter for a given arrangement of a second receiver, as a means of maximizing the transmission efficiency (TE). Using this theoretical analysis, it is revealed that the TE can be improved by locating the first receiver far from the transmitter when the first receiver has higher quality factor or the distance between the transmitter and the second receiver is lower. Results for various cases show that our analytical results are in a good agreement with experimental ones.

An Internet-of-Things (IoT) cellular network is considered in which IoT devices communicate with an IoT base station using IoT sub-bands placed between long-term evolution (LTE) bands. Due to spectral leakage, inter-band interference exists among IoT sub-bands and also between LTE and IoT bands. It is assumed that the IoT cellular network is responsible for reducing its interference to the LTE network to a certain threshold level. Under such interference regulation to LTE bands, we establish a joint sub-band assignment and power allocation optimization in order to maximize the sum rate of the IoT cellular network. A novel two-stage suboptimal algorithm that sequentially performs sub-band assignment and power control is proposed, reflecting the impact of spectral leakage in its optimization procedure. Simulation results demonstrate that the proposed algorithm considering the impact of spectral leakage outperforms the conventional optimization algorithms without considering spectral leakage. It is further shown that it provides almost the same sum rate achievable for a stand-alone network as if there were no LTE networks.

A novel blind interference alignment (IA) scheme in conjunction with interference decoding by virtue of integer forcing is proposed for downlink cellular networks without channel state information at the base station. In the proposed scheme, inter-user interference at each mobile user is aligned in blind manner, and by employing the same lattice code for all users, each user directly decodes integer-linear combinations of interfering codewords from the aligned interference signals in contrast to the previous works that simply null out the aligned interference by zero forcing. Numerical simulations demonstrate that the proposed scheme significantly improves the sum rate compared with the previous blind IA schemes.

Subpixel-based image down-sampling has been widely used to improve the apparent resolution of down-sampled images on display. However, previous subpixel rendering methods often introduce distortions, such as aliasing and color-fringing. This study proposes a novel subpixel rendering method that uses selective sampling and optimal filtering. We first generalize the previous frequency domain analysis results indicating the relationships between various down-sampling patterns and the aliasing artifact. Based on this generalized analysis, a subpixel-based down-sampling pattern for each image is selectively determined by utilizing the edge distribution of the image. Moreover, we investigate the origin of the color-fringing artifact in the frequency domain. Optimal spatial filters that can effectively remove distortions caused by the selected down-sampling pattern are designed via frequency domain analyses of aliasing and color-fringing. The experimental results show that the proposed method is not only robust to the aliasing and color-fringing artifacts but also outperforms the existing ones in terms of information preservation.

For the measurement of abrupt and large surface movements caused by earthquakes, volcanic eruption and melting glacier, Synthetic aperture radar (SAR) offset tracking method would be a feasible solution because it can provide unambiguous ground displacements in both the ground range and azimuth directions when the interferometric phase is not coherent. However, the measurement performance of the method largely depends on the kernel size, which denotes the size of search window to estimate the azimuth and range offsets between reference and target SAR images. Thus, there is a trade-off between sensitivity and measurement density depending on the search kernel size. In this study, an enhanced SAR offset tracking method based on multi-kernel processing has been developed to find an optimized measurement from the trade-off between resolution and measurement accuracy. It can obtain optimal surface displacement measurements by calculating multiple offset measurements and determining a final measurement from the statistical properties of the multiple measurements. The measurement performance of the proposed method was evaluated by using European Remote Sensing 2 (ERS-2) satellite SAR data sets of the Hector Mine earthquake event in 1999 and Advanced Land Observing Satellite-2 Phased Array type L-band Synthetic Aperture Radar-2 (ALOS-2 PALSAR-2) data sets of the 2016 Kumamoto earthquake event. Our results showed that an optimized measurement from the trade-off between the observation accuracy and resolution can be effectively determined by our proposed processing strategy. The results are improved results for measurement density and accuracy over previously published results. It further confirmed that our new method is allowed for the optimal measuring the large-scale fast surface displacements that cannot be sufficiently observed with the phase-based SAR method.

Ultra-short throw projectors (USTPs) that reduce throw distance greatly with a high resolution have been widely developed. However, the hardware characteristics of the USTP make projected image distorted easily comparing to the typical long throw projectors (LTPs). Therefore, keystone correction is an important feature to ensure the usability of the USTPs. Although many automatic keystone correction methods have been presented for the LTP, they are limited to be directly applied to the USTP. Due to this limitation, the commercial USTPs adopted a manual keystone correction. The manual method requires users to be familiar with keystone distortion and correction mechanism, otherwise it takes lots of time to complete and results are unsatisfactory. To solve this problem, we propose a novel keystone correction method with the touch interface. As a prerequisite of keystone correction, we need to know the optimal projected shape without distortion. In the proposed method, the user-specified shape which obtained from the touch interface is used as the optimal shape. In addition, we present the projection model which can explain the cause and the solution of the keystone distortion. Experimental results show that the proposed method outperforms the manual keystone correction in terms of correction performance and usability.

Wireless device-to-device (D2D) caching networks are studied, in which n nodes are distributed uniformly at random over the network area. Each node caches M files from the library of size m &ge, M and independently requires a file from the library. Each request will be served by cooperative D2D transmission from other nodes having the requested file in their cache memories. In many practical sensor or Internet of things (IoT) networks, there may exist simple sensor or IoT devices that are not able to perform real-time rate and power control based on the reported channel quality information (CQI). Hence, it is assumed that each node transmits a file with a fixed rate and power so that an outage is inevitable. To improve the outage-based throughput, a cache-enabled interference cancellation (IC) technique is proposed for cooperative D2D file delivery which first performs IC, utilizing cached files at each node as side information, and then performs successive IC of strongly interfering files. Numerical simulations demonstrate that the proposed scheme significantly improves the overall throughput and, furthermore, such gain is universally achievable for various caching placement strategies such as random caching and probabilistic caching.

Despite many kinds of research on pressure-retarded osmosis (PRO), feasibility studies for PRO are still insufficient. To provide a better understanding of PRO-hybridized processes, an energy efficiency analysis should reflect the hybridization features of three processes, including PRO, seawater reverse osmosis (SWRO), and membrane distillation (MD). To this end, a new dimensionless (i.e., unitless or scale-free) performance index is proposed to facilitate a fair comparison of energy efficiency between SWRO-PRO and SWRO-MD-PRO. The new performance index physically implies a ratio of the total energy recovered by PRO to the total energy consumed by SWRO and MD. The performances of hybridized processes were estimated with the new index and compared to each other after running several simulations. The simulation results showed that SWRO-MD-PRO generally has a higher energy efficiency than SWRO-PRO if an inexpensive heat source, such as waste heat, is used. However, the energy efficiencies of both PRO-hybridized processes were different according to the simulation conditions. Therefore, it can be concluded that energy optimization for PRO-hybridized processes should be conducted differently than for SWRO. The results from this study are expected to play a key role in providing a new roadmap for PRO-hybridized process research.