• 한국정보통신학회논문지
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• 제24권6호
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• pp.744-750
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• 2020

본 논문에서는 무선통신 시스템의 주파수 효율과 에너지 효율을 개선하기 위하여 딥러닝 기반의 송신 전력 제어 기법을 제안한다. 무선통신 시스템에서 다수의 송수신기의 위치는 균일 분포를 따르고 송수신기 간 채널은 나카가미 페이딩 채널을 가정하여 제안하는 송신 전력 제어 기법에 대한 주파수 효율과 에너지 효율의 성능을 분석한다. 제안하는 송신 전력 제어 기법은 딥러닝 기반의 학습에서 주파수 효율과 에너지 효율을 개선하기 위하여 배치 정규화 기법을 이용한다. 시뮬레이션을 통해 송수신기의 위치 범위를 제한하는 지형적 크기와 나카가미 페이딩 지수에 대하여 제안하는 송신 전력 제어 기법과 기존의 송신 전력 제어 기법의 주파수 효율과 에너지 효율의 성능 결과를 비교한다. 성능 결과의 비교를 통해 제안하는 기법이 기존의 기법보다 우수한 성능을 제공함을 입증한다.

• ETRI Journal
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• 제43권3호
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• pp.389-399
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• 2021

In this paper, we propose one-bit feedback-based distributed beamforming (DBF) techniques for simultaneous wireless information and power transfer in interference channels where the information transfer and power transfer networks coexist in the same frequency spectrum band. In a power transfer network, multiple distributed energy transmission nodes transmit their energy signals to a single energy receiving node capable of harvesting wireless radio frequency energy. Here, by considering the Internet-of-Things sensor network, the energy harvesting/information decoding receivers (ERx/IRx) can report their status (which may include the received signal strength, interference, and channel state information) through one-bit feedback channels. To maximize the amount of energy transferred to the ERx and simultaneously minimize the interference to the IRx, we developed a DBF technique based on one-bit feedback from the ERx/IRx without sharing the information among distributed transmit nodes. Finally, the proposed DBF algorithm in the interference channel is verified through the simulations and also implemented in real time by using GNU radio and universal software radio peripheral.

• ETRI Journal
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• 제39권6호
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• pp.794-802
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• 2017

In this paper, a wireless powered communication network (WPCN) consisting of a hybrid access point (H-AP) and multiple user equipment (UE), all of which operate in full-duplex (FD), is described. We first propose a transceiver structure that enables FD operation of each UE to simultaneously receive energy in the downlink (DL) and transmit information in the uplink (UL). We then provide an energy usage model in the proposed UE transceiver that accounts for the energy leakage from the transmit chain to the receive chain. It is shown that the throughput of an FD WPCN using the proposed FD UE (FD-WPCN-FD) can be maximized by optimal allocation of the UL transmission time to the UE by solving a convex optimization problem. Simulation results reveal that the use of the proposed FD UE efficiently improves the throughput of a WPCN with a practical self-interference cancellation capability at the H-AP. Compared to the WPCN with FD H-AP and half-duplex (HD) UE, FD-WPCN-FD achieved an 18% throughput gain. In addition, the throughput of FD-WPCN-FD was shown to be 25% greater than that of WPCN in which an H-AP and UE operated in HD.

• 전자공학회논문지
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• 제52권6호
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• pp.3-9
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• 2015

본 논문에서는 짧은 지연시간을 요구하는 CDMA 시스템 환경에서 전송률 스케줄링과 전력량 할당 문제를 연구한다. 구체적으로, 본 논문은 각각의 단말이 짧은 구간 동안의 평균 전송률을 유지하는 동시에 에너지 효율적인 스케줄링 방안을 제안한다. 다중 코드를 적용한 CDMA 시스템을 고려하며, 각각의 코드는 가상의 사용자로 해석할 수 있다. 논문의 최종 목적은 전송률 과정에서 소모하는 에너지가 최소화되도록 각각의 시간슬럿에 가상의 사용자를 스케줄링하는 방안을 제안하는 것이다. 주목할만한 점은, 본 논문에서 고려하는 전송률 최적화 문제가 최단 경로 알고리즘으로 해결 가능하다는 점이다. 마지막으로, 본 논문이 제안하는 에너지 최적화 스케줄링 방안을 TDMA 형식의 스케줄링 방안과 성능 비교 분석한다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(5)
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• pp.199-202
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• 2000

RFID (Radio Frequency Identification) is a technique which is used for identifying different types of objects and tracking people and animals. Passive RFID consists of reader, a passive tag. The reader transmit energy to a tag and read information back from tag. The tag is energized by a carrier frequency which is transmitted by the reader and transmit information back to the reader. In this paper, the circuit for read and write RFID system is presented. The presented RFID system adopts 125kHz carrier frequency, backscattering and PSK for communication method.

• Journal of Communications and Networks
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• 제18권5호
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• pp.688-698
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• 2016

In this paper, we investigate the achievable sum rate and energy efficiency of downlink massive multiple-input multiple-output antenna systems with zero-forcing precoding, by taking into account the randomness of user locations. Specifically, we propose two types of non-uniform user distributions, namely, center-intensive user distribution and edge-intensive user distribution. Based on these user distributions, we derive novel tight lower and upper bounds on the average sum rate. In addition, the impact of user distributions on the optimal number of users maximizing the sum rate is characterized. Moreover, by adopting a realistic power consumption model which accounts for the transmit power, circuit power and signal processing power, the energy efficiency of the system is studied. In particular, closed-form solutions for the key system parameters, such as the number of antennas and the optimal transmit signal-to-noise ratio maximizing the energy efficiency, are obtained. The findings of the paper suggest that user distribution has a significant impact on the system performance: for instance, the highest average sum rate is achieved with the center-intensive user distribution, while the lowest average sum rate is obtained with the edge-intensive user distribution. Also, more users can be served with the center-intensive user distribution.

• 전자공학회논문지
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• 제51권11호
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• pp.33-39
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• 2014

본 논문에서는 다중 사용자 다중 안테나 하향링크 시스템에서 maximal ratio transmission (MRT) 기법 사용 시, 에너지 효율을 최대화하는 최적의 송신 안테나 수에 대해 알아본다. Full channel state information at the transmitter (CSIT) 환경에서 평균 채널 이득, 각 단말 간 채널 독립성, 평균 path loss를 사용하여 최적화 식을 근사하고 편미분을 이용하여 closed form으로 최적의 송신 안테나 수를 구한다. 또한 limited feedback 환경에서는 동일한 방법으로 근사한 목적함수에 대하여 bisection method를 이용하여 최적의 송신 안테나 수를 찾는다. 모의실험 결과를 통해, 구해진 최적의 송신안테나 수가 exhaustive search로 찾은 최적의 송신안테나 수에 비해 오차가 크지 않음을 확인하고, 단말의 피드백 비트 수가 최적의 송신 안테나 수에 미치는 영향을 분석한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권4호
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• pp.1889-1910
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• 2017

This paper investigates a protocol so-called Adaptive Harvest Then Transmit (AHTT) for wireless powered communication networks (WPCNs) in multiple-input single-output (MISO) downlink systems, which assists in transmitting signals from a multi-antenna transmitter to a single-antenna receiver. Particularly, the power constrained relay is supplied with power by utilizing radio frequency (RF) signals from the source. In order to take advantage of multiple antennas, two different linear processing schemes, including Maximum Ratio Combining (MRC) and Selection Combination (SC) are studied. The system outage capacity and ergodic capacity are evaluated for performance analysis. Furthermore, the optimal power allocation is also considered. Our numerical and simulation results prove that the implementation of multiple antennas helps boost the energy harvesting capability. Therefore, this paper puts forward a new way to the energy efficiency (EE) enhancement, which contributes to better system performance.

• 한국통신학회논문지
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• 제34권2A호
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• pp.107-112
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• 2009

Spectral efficiency of current two-phase cooperative communications protocols is low since in the second time the relay forwards the same signal received from the source to the destination, the source keeps silent in this time. In this paper, we propose a novel cooperative communications protocol where the signal needed to transmit to the destination is sent in both phases, the source and the relay also transmit different signal to the destination thus no loss of spectral efficiency. This protocol performs signal selection based on log-likelihood ratio (LLR) at relay and maximum likelihood (ML) detection at destination. While existing protocols pay for a worse performance than direct transmission in the low SNR regime which is of special interest in ad hoc networks, ours is better over the whole range of SNR. In addition, the proposal takes advantages of bandwidth efficiency, long delay and interference among many terminals in ad hoc network. Simulation results show that the proposed protocol can significantly save total energy for wireless ad hoc networks.

• Interaction and multiscale mechanics
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• 제7권1호
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• pp.543-561
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• 2014

We present a full energy and force formulation of the quasicontinuum method with non-local and local transition elements. Non-local transition elements are developed to transmit inhomogeneity from the atomistic to the continuum regions. Local transition elements are developed to resolve the mathematical mismatch between non-local atoms and the local continuum. The rationale behind these transition elements is provided by analyzing the energy and force transitions between atoms and continuum under the Cauchy-Born rule. We show that breakdown of the Cauchy-Born rule occurs for slaved atoms of local elements within the cutoff of non-local atoms. The inadequacy of the Cauchy-Born rule at the transition region naturally leads to the need of atomistic treatment of transition slaved and transition representative atoms. Such an atomistic treatment together with a full or cutoff sampling allows non-local transition elements containing these transition entities to transmit inhomogeneity. Different force formulations for transition representative atoms and pure local representative atoms allow the local transition elements to resolve non-local and local mismatches. The method presented herein is validated by force calculations in an unstressed perfect crystal as well as an unrelaxed grain boundary model. A nanoindentation simulation in 3D is conducted to demonstrate the accuracy and efficiency of the proposed method.