• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권9호
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• pp.3172-3193
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• 2022

Cognitive radio-simultaneous wireless information and power transfer (CR-SWIPT) has attracted much interest since it can improve both the spectrum and energy efficiency of wireless networks. This paper focuses on the resource sharing between a point-to-point primary system (PRS) and a multiuser multi-antenna cellular cognitive radio system (CRS) containing a large number of cognitive users (CUs). The resource sharing optimization problem is formulated by jointly scheduling CUs and adjusting the transmit power at the cognitive base station (CBS). The effect of accessing CUs' spatial channel correlation on the possible transmit power of the CBS is investigated. Accordingly, we provide a low-complexity suboptimal approach termed the semi-correlated semi-orthogonal user selection (SC-SOUS) algorithm to enhance the spectrum efficiency. In the proposed algorithm, CUs that are highly correlated to the information decoding primary receiver (IPR) and mutually near orthogonal are selected for simultaneous transmission to reduce the interference to the IPR and increase the sum rate of the CRS. We further develop a spatial correlation-based resource sharing (SC-RS) strategy to improve energy sharing performance. CUs nearly orthogonal to the energy harvesting primary receiver (EPR) are chosen as candidates for user selection. Therefore, the EPR can harvest more energy from the CBS so that the energy utilization of the network can improve. Besides, zero-forcing precoding and power control are adopted to eliminate interference within the CRS and meet the transmit power constraints. Simulation results and analysis show that, compared with the existing CU selection methods, the proposed low-complex strategy can enhance both the achievable sum rate of the CRS and the energy sharing capability of the network.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권7호
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• pp.1777-1791
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• 2012

This paper considers a downlink cognitive radio (CR) network where one secondary user (SU) and one primary user (PU) share the same base station (BS). The spectrum of interest is divided into a set of independent, orthogonal subchannels. The communication of the PU is of high priority and the quality of service (QoS) is guaranteed by the minimum rate constraint. On the other hand, the communication of the SU is of low priority and the SU opportunistically accesses the subchannels that were previously discarded by the PU during power allocation. The BS assigns fractions ?? and 1 ?? of the total available transmit power to the PU and the SU respectively. Two power allocation schemes with opportunistic subchannel access are proposed, in which the optimal values of ??'s are also obtained. The objective of one scheme is to maximize the rate of the SU, and the objective of the other scheme is to maximize the sum rate of the SU and the PU, both under the PU minimum rate constraint and the total transmit power constraint. Extensive simulation results are obtained to verify the effectiveness of the proposed schemes.

• 한국통신학회논문지
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• 제37권8A호
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• pp.632-638
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• 2012

이동통신시스템의 이동국이 소프트 핸드오프 상황에 놓여 있을 때, 제안되어 실제 시스템에 적용되고 있는 상향 링크 송신 전력 제어 방법의 성능을 다양한 환경에서 컴퓨터 시뮬레이션을 통하여 분석한다. 분석결과 소프트 핸드오프 중에는 두 기지국이 개별 수신한 데이터의 품질보다 기지국 제어기에서 선택 결합한 후의 데이터 품질이 더 나음을 확인한다. 또한, 목표 프레임 오류율을 달성하기 위한 외부 루프 전력 제어는 각 기지국에서가 아니라 기지국 제어기에서 이뤄져야 단말이 불필요한 송신 에너지를 소비하지 않고 보다 효과적으로 목표 프레임 오류율을 달성할 수 있음을 컴퓨터 시뮬레이션을 통해 확인한다.

• 한국통신학회논문지
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• 제34권4A호
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• pp.316-323
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• 2009

본 논문은 셀간 간섭을 제어하여 셀 경계 사용자의 데이터 전송율을 증가시키는 기술인 소프트 주파수 재사용시 전력 할당에 관한 것이다. 소프트 주파수 재사용 기술은 셀 경계 사용자의 데이터 전송율을 개선하는데 유용한 기술이나 주파수 재사용 지수가 증가되어 셀 평균 데이터 전송율을 감소시키는 문제가 있다. 본 논문에서는 하나의 중앙 제어기가 물리적 거리가 인접한 여러 개의 셀을 제어하는 환경에서, 셀 경계 사용자의 데이터 전송율 개선하면서도 셀 평균 전송율 감소를 최소화하도록 소프트 주파수 재사용을 위한 송신 전력 할당 기법을 제안한다. 시스템 시뮬레이션을 통하여 인접한 두 셀에 소프트 주파수 재사용 기술을 적용하여 소프트 주파수 재사용에 의한 셀 평균 데이터 전송율 감소 정도와 제안하는 전력 할당 기법에 의한 셀 평균 데이터 전송을 개선을 살펴본다.

• Journal of Communications and Networks
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• 제18권2호
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• pp.173-181
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• 2016

In this paper, we address a new robust optimization problem in a multiuser multiple-input single-output broadcasting system with simultaneous wireless information and power transmission, where a multi-antenna base station (BS) sends energy and information simultaneously to multiple users equipped with a single antenna. Assuming that perfect channel-state information (CSI) for all channels is not available at the BS, the uncertainty of the CSI is modeled by an Euclidean ball-shaped uncertainty set. To optimally design transmit beamforming weights and receive power splitting, an average total transmit power minimization problem is investigated subject to the individual harvested power constraint and the received signal-to-interference-plus-noise ratio constraint at each user. Due to the channel uncertainty, the original problem becomes a homogeneous quadratically constrained quadratic problem, which is NP-hard. The original design problem is reformulated to a relaxed semidefinite program, and then two different approaches based on convex programming are proposed, which can be solved efficiently by the interior point algorithm. Numerical results are provided to validate the robustness of the proposed algorithms.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.680-683
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• 1999

A thyristor controlled shunt compensator, which is installed in the middle of the transmission line is adopted for controlling real power flow in a simple power transmission system. By means on the Fourier series representation of the thyristor switching action and the system parameters, the thyristor current equations are derived, which transmit the required real power of the simple power transmission system and inform the thyristor firing angle, the thyristor conduction angle, the power flows and the harmonic characteristics EMTP simulations at the various operating points show the dynamic characteristics of the thyristor controlled shunt compensator and correspond to the results calculated with the Fourier series representation.

• 한국군사과학기술학회지
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• 제23권1호
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• pp.59-65
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• 2020

Many technologies are being studied to reduce the RCS(Radar Cross Section) of stealth aircraft. Most RCS-reduction technlogies correspond to platforms. It is important to identify factors that RCS performance through simulation analysis of aircraft Mounted equipment. In particular, there are no studies of RCS performance in the radar frequency band when antenna transmit signals are applied. In this paper, the RCS performance variation on the transmit signal on/off of antennas mounted on a stealth aircraft was verified. Antennas were selected for each frequency band and simulated analysis to the RCS performance changes during antenna transmitting signal. Finally, to verify the characteristics of the change in RCS performance, RCS test measurements on the low-profile antenna transmit signal on/off were performed. In addintion, antenna RCS test measurement was performed according to the change of transmit signal power output. As a result, it was confirmed that there is no change in RCS performance when an antenna transmit signal is applied.

• 한국통신학회논문지
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• 제30권9A호
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• pp.788-794
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• 2005

In this paper, we focus on the potential of dual polarized antennas in mobile system. thus, this paper designs exact dual polarized channel with Spatial Channel Model (SCM) and investigates the performance for certain environment. Using proposed the channel model; we know estimates of the channel capacity as a function of cross polarization discrimination (XPD) and spatial fading correlation. It is important that the MIMO channel matrix consists of Kronecker product dividable spatial and polarized channel. Through the channel characteristics, we propose an algorithm for the adaptation of transmit antenna configuration to time varying propagation environments. The optimal active transmit antenna subset is determined with equal power allocated to the active transmit antennas, assuming no feedback information on types of the selected antennas. We first consider a heuristic decision strategy in which the optimal active transmit antenna subset and its system capacity are determined such that the transmission data rate is maximized among all possible types. This paper then proposes singular values decision procedure consisting of Kronecker product with spatial and polarize channel. This method of singular value decision, which the first channel environments is determined using singular values of spatial channel part which is made of environment parameters and distance between antennas. level of correlation. Then we will select antenna which have various polarization type. After spatial channel structure is decided, we contact polarization types which have considerable cases It is note that the proposed algorithms and analysis of dual polarized channel using SCM (Spatial Channel Model) optimize channel capacity and reduce the number of transmit antenna selection compare to heuristic method which has considerable 100 cases.

• 전자공학회논문지
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• 제50권4호
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• pp.3-8
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• 2013

최근 들어 CDMA 기반 시스템에서 고속 데이터 서비스 지원을 위한 수신 성능 개선 방법의 하나로 칩 단위에서 동작하는 선형 최소 평균 제곱 오차(LMMSE: linear minimum mean-squared error) 수신기에 대한 연구가 활발히 진행되고 있다. 본 논문에서는 D-TxAA (dual stream transmit antenna array) 방식을 사용하는 단일 스트림(single stream) HSDPA MIMO 시스템에서 선부호화 계수(precoding weight) 적용이 LMMSE 수신기의 성능에 미치는 영향을 분석하고자 한다. 우선 D-TxAA 기반 $2{\times}2$ 다중입력 다중출력(MIMO: multiple input multiple output) 시스템에서 수신 신호 순간 파워 (instantaneous power)의 총 합이 최대가 되도록 하는 선부호화 계수 결정 방식을 유도할 것이다. 또한 선부호화 계수의 적용 지연 시간과 단말의 이동 속도가 LMMSE 수신기의 성능에 미치는 영향을 분석하고, 컴퓨터 모의실험을 통해 검증하고자 한다.

• 한국기계가공학회지
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• 제16권6호
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• pp.153-158
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• 2017

Reducer is a device to transmit and change torque and speed from drive shaft to driven shaft with excellent transmission efficiency, and it is widely used in many areas today. Reduction gear consists of two axes, gear, bearing supporting axes, and housing. The simplest method to transmit rotation or power to multiple axes is to attach circular plates to two axes and contact each other. However, in this case, if increasing number of rotations or if contact pressure is small, because of slipping, it cannot transmit power. For problems for the current reducer case, it is heavy and its assembling and repair is difficult. In addition, there are few studies about manufacturing and performance testing of worm gear reducer, causing lack of the foundation to improve the product competition and the performance.