We developed an optical neural network (ONN) for efficient processing and recognition of 2-dimensional (2D) images, employing a conventional liquid crystal display panel as optical neurons and ...synapses. This configuration allowed for optical signal outputs proportional to matrix-vector multiplication for 2D image inputs. However, our experimental results revealed a 26.6% decrease in the optical classification accuracy, despite utilizing digitally pre-trained parameters with 100% accuracy for 500 handwritten digits. This decline can be attributed to system imperfections associated with non-ideal functions of optical components and optical alignment. Rather than pursuing an elusive, imperfection-free ONN or attempting to calibrate these defects individually, we addressed these challenges by introducing a self-correction mechanism that utilizes a machine learning algorithm. This approach effectively restored the recognition accuracy and minimized loss of our ONN to levels comparable to the digitally pre-trained model. This study underscores the potential of constructing defect-tolerant hardware in ONNs through the application of machine learning techniques.
In this paper, we propose a uplink (UL) non-orthogonal multiple access (NOMA) systems equipped with multiple antennas to enhance the sum capacity of UL. In the proposed UL NOMA system, a base station ...(BS) with N antennas can support 2N users by sharing the space resource. However, sharing the space resource leads to interference between users. Therefore, to mitigate the interference and improve the sum capacity, we additionally propose a set selection algorithm and power control scheme. The set selection algorithm, which selects 2N users based on orthogonality and gain-difference between their channels, reduces the interference between users. Furthermore, the power control scheme can maximize the sum capacity with ensuring minimum target rate. Numerical results show that the proposed system improves the sum capacity over that of the conventional orthogonal multiple access (OMA) system.
In this letter, we propose a novel hybrid type of power-domain non-orthogonal multiple access (NOMA) in downlink environments, called partial NOMA (P-NOMA). In conventional NOMA, where the signals of ...user equipments (UEs) are fully overlapped, the utilization of the bandwidth can be maximized, but doing so also maximizes the interference from the other UEs. P-NOMA partially overlaps the UEs' signals by controlling the extent of the overlap and can thus reduce the interference from other UEs. To verify whether this is a possibility with P-NOMA, we observed the performance tendency of the achievable rate versus the overlap ratio and then confirmed that there is an overlap ratio that achieves performance that is better than that of conventional NOMA with respect to the sum of the achievable rate. In other words, slightly reducing the overlap ratio improves the sum of the achievable rate compared to the full overlap ratio.
We consider a mixed numerology spectrum sharing (SS) system where the users have different subcarrier spacing (SCS). Unlike in single numerology SS systems, mixed numerology SS systems suffer from ...inter-numerology interference (INI). We first derive the interference pattern and find that the variance of interference energy increases due to the difference in SCS. This increase in variance negatively affects decoding performance, since the interference energy is unbalanced between subcarriers. However, previous works on this issue did not take this interference pattern into account for interference management. In order to suppress the increase in variance of the interference energy, we propose a transceiver structure for large SCS users by using simple cyclic shift and frequency shift operations. The proposed transceiver disperses the effect of INI, reducing the variance in the interference energy. From the derived distribution characteristics of the interference energy in closed-form expressions, we show that the proposed transceiver achieves better decoding performance.
We investigate the impact of the time offset (TO) and carrier frequency offset (CFO) on the performance of a filter bank multicarrier - quadrature amplitude modulation (FBMC-QAM) system. As opposed ...to conventional FBMC system where offset QAM (OQAM) is utilized due to the intrinsic interference, the FBMC-QAM system cancels the intrinsic interference based on the orthogonality conditions between the two kinds of filters. Because the FBMC-QAM system uses two kinds of filters, the effects on the TO and CFO are different compared to the conventional FBMC system. The performance of this system is degraded by TO because the two-filter orthogonality conditions are not satisfied, resulting in severe inter-symbol interference (ISI). With respect to the CFO, the orthogonality between the two filters protects from performance degradation caused by intercarrier interference (ICI). Numerical results show that FBMCQAM is more robust against CFO while it is more sensitive to TO compared to the FBMC-OQAM system.
In this paper, we propose a non-orthogonal multiple access-based multiuser beamforming (NOMA-BF) system designed to enhance the sum capacity. In the proposed NOMA-BF system, a single BF vector is ...shared by two users, so that the number of supportable users can be increased. However, sharing a BF vector leads to interference from other beams as well as from the other user sharing the BF vector. Therefore, to reduce interference and improve the sum capacity, we additionally propose a clustering and power allocation algorithm. This clustering algorithm, which selects two users with high correlation and a large gain-difference between their channels, can reduce the interference from other beams and from the other user as well. Furthermore, power allocation ensures that each user's transmit power is allocated so as to maximize the sum capacity. Numerical results verify that the proposed NOMA-BF system improves the sum capacity, compared to the conventional multiuser BF system.
Abundant Li resources in the ocean are promising alternatives to refining ore, whose supplies are limited by the total amount and geopolitical imbalance of reserves in Earth's crust. Despite advances ...in Li
extraction using porous membranes, they require screening other cations on a large scale due to the lack in precise control of pore size and inborn defects. Herein, MoS
nanoflakes on a multilayer graphene membrane (MFs-on-MGM) that possess ion channels comprising i) van der Waals interlayer gaps for optimal Li
extraction and ii) negatively charged vertical inlets for cation attraction, are reported. Ion transport measurements across the membrane reveal ≈6- and 13-fold higher selectivity for Li
compared to Na
and Mg
, respectively. Furthermore, continuous, stable Li
extraction from seawater is demonstrated by integrating the membrane into a H
and Cl
evolution system, enabling more than 10
-fold decrease in the Na
concentration and near-complete elimination of other cations.
Abundant Li resources in the ocean are promising alternatives to refining ore, whose supplies are limited by the total amount and geopolitical imbalance of reserves in Earth's crust. Despite advances ...in Li+ extraction using porous membranes, they require screening other cations on a large scale due to the lack in precise control of pore size and inborn defects. Herein, MoS2 nanoflakes on a multilayer graphene membrane (MFs‐on‐MGM) that possess ion channels comprising i) van der Waals interlayer gaps for optimal Li+ extraction and ii) negatively charged vertical inlets for cation attraction, are reported. Ion transport measurements across the membrane reveal ≈6‐ and 13‐fold higher selectivity for Li+ compared to Na+ and Mg2+, respectively. Furthermore, continuous, stable Li+ extraction from seawater is demonstrated by integrating the membrane into a H2 and Cl2 evolution system, enabling more than 104‐fold decrease in the Na+ concentration and near‐complete elimination of other cations.
MoS2 passivated multilayer graphene membrane provides the ionic channels for Li+ extraction from seawater. The ion transport measurement of the membrane reveals ≈6‐ and 13‐fold higher selectivity for Li+ compared to Na+ and Mg2+, respectively. In addition, the continuous Li+ extraction system from seawater shows more than 104‐fold decrease in the Na+ concentration and near‐perfect elimination of other cations.
There is a global focus on adding renewable energy sources to the mix of energy supplies. In this study, the grid connections for large-scale offshore wind farms in areas that have high penetration ...of renewable energy sources were examined. System strength evaluation considering the interaction of wind farms and inverter-based resources (IBRs) was performed; the fault current was then analyzed to determine their contribution to the total fault current at a bus level. These studies revealed that the interaction between offshore wind farms and IBRs may make the power system weaker, and it is possible that fault current contributions from offshore wind farms can violate the capacity limit of existing circuit breakers. The results of steady-state analysis were verified through case studies focused on the southwest area of the Korea Electric Power Corporation (KEPCO) system where large-scale offshore wind farms are planned to be established and connected. Power system planners will benefit from the results of this study with a better understanding of the factors to consider when integrating large-scale wind farms in areas with high penetration of renewables.
In this paper, we consider the user fairness in partial non-orthogonal multiple access (P-NOMA) system which was proposed in our previous work. In the P-NOMA system, the interference of NOMA can be ...managed by adjusting the overlap ratio between users. In our previous works, we considered the enhancement of sum of achievable rate. In this paper, we investigate the performance of P-NOMA in terms of user fairness. For reflecting user fairness on P-NOMA systems, we first define the metric to represent user fairness and then observe the target performance metric according to overlap ratio. In addition, we propose a feasible operating method to achieve the user fairness.
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