• 한국정보통신학회논문지
• /
• 제10권4호
• /
• pp.752-757
• /
• 2006

고속데이터 전송이 요구되는 경우, OFDM(Orthogonal Frequency Division Multiplexing)은 다중경로에 의해 발생되는 주파수 선택성 페이딩에 쉽게 대처할 수 있다는 장점 때문에 다양한 고속 무선 통신 시스템에 채택되어왔다. 본 논문에서는 최적의 적응 비트로딩 알고리즘을 제안하고, 이를 확인하기 위해 SISO(Single Input Single Output)-OFDM 시스템에 이 알고리즘을 적용하고 고정 변조를 사용하는 SISO-OFDM과 비교 분석 하였다. 특히 다중 경로페이딩 채널에서 채널을 알고 있는 경우, MIMO(Multiple Input Multiple Output) 시스템의 적응 비트로딩을 시험하기 위해, 특이치 분해(SVD : Singular Value Decomposition)를 사용하여 MIMO 채널을 SISO 채널로 병렬 분해하여, 제안한 적응비트로딩 알고리즘을 적용하였다. 시뮬레이션 결과, 적응 비트로딩 MIMO-OFDM 시스템은 SISO-OFDM 시스템 보다 BER 성능이 우수함을 확인하였다.

• 대한전자공학회논문지TC
• /
• 제44권4호
• /
• pp.10-16
• /
• 2007

본 논문은 MMSE 수신기를 가지는 MIMO MC-CDMA시스템에서의 출력 SINR을 분석한다. 단일 안테나에서의 분석을 위한 가정들이 다중안테나에 바로 확장 적용되지 않기 때문에 단일 안테나를 가지는 MC-CDMA시스템에 대한 기존의 성능 분석은 MIMO MC-CDMA 시스템에 바로 적용하지 못한다. 그러므로 본 논문에서는 Marcenko Pastur law와 확장된 Haar 유니터리 행렬의 특성을 이용하여 MIMO system에 대한 성능 분석을 시도한다. 분석을 통해 확산 코드 길이가 무한대로 갈 때 출력 SINR이 특정값으로 접근함을 보이고 그 값을 freeness가정을 통해 구하여 비트 오차확률을 구하고 실험과 비교한다.

• 한국통신학회논문지
• /
• 제38A권5호
• /
• pp.443-450
• /
• 2013

본 논문에서는 셀룰러 시스템 상향 링크에서 가상 여러입력 여러출력 (multiple input multiple output: MIMO)를 적용할 때 사용자 쌍 선택 및 자원 할당 문제를 고려한다. 다중 접속 방식으로 LTE (long term evolution) 시스템의 SC-FDMA (single carrier frequency division multiple access)보다 자원 할당이 유연한 DFTS-OFDMA(discrete Fourier transform spread orthogonal FDMA) 방식을 적용하고 서로 다른 제약 조건에서 전송률을 최대로 하는 사용자 쌍 및 자원 할당 최적화 문제를 공식화하였다. 이 때 비연속 부반송파 자원을 할당하고 중복 사용자 할당을 허용하는 DFTS-OFDMA 방식은 SC-FDMA보다 전달해야 할 자원 할당 제어 정보 양은 늘어나지만 최적화 해를 쉽게 얻을 수 있고 전송률을 향상시킴을 볼 수 있다.

• 대한전기학회논문지
• /
• 제39권3호
• /
• pp.301-311
• /
• 1990

A multiple controller structure consisting of a typical feedback controller and an additive redundant controller is proposed for enhancing the reliability of the control system. For the case where the main controller is chosen as a pole assignment controller with input/output measurements and the redundant controller as the Model Reference Adaptive Controller (MRAC) whose reference model is the closed-loop combination of the plant and the main controller, it is proven that the tracking error between the command input and plant output converges to zero under failure in one of the controllers or parameter perturbations of the plant, and further that the reliability measured by Mean Time To Failure (MTTF) is greater than that of the system with only a single main controller. A simulation Example is provided to illustrate reliable operation of the proposed control system against the controller failure.

• ETRI Journal
• /
• 제32권2호
• /
• pp.222-229
• /
• 2010

A conventional pseudorandom sequence generator creates only 1 bit of data per clock cycle. Therefore, it may cause a delay in data communications. In this paper, we propose an efficient implementation method for a pseudorandom sequence generator with parallel outputs. By virtue of the simple matrix multiplications, we derive a well-organized recursive formula and realize a pseudorandom sequence generator with multiple outputs. Experimental results show that, although the total area of the proposed scheme is 3% to 13% larger than that of the existing scheme, our parallel architecture improves the throughput by 2, 4, and 6 times compared with the existing scheme based on a single output. In addition, we apply our approach to a $2{\times}2$ multiple input/multiple output (MIMO) detector targeting the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) system. Therefore, the throughput of the MIMO detector is significantly enhanced by parallel processing of data communications.

• Current Optics and Photonics
• /
• 제1권4호
• /
• pp.289-294
• /
• 2017

A high-performance time-division multiplexing (TDM) -based multiuser (MU) multiple-input multipleoutput (MIMO) system for efficient indoor visible-light communication (VLC) is presented. In this work, a MIMO technique based on RGB light-emitting diodes (LEDs) with selection combining (SC) is utilized for data transmission. That is, the proposed scheme employs RGB LEDs for parallel transmission of user data and transmits MU data in predefined slots of a time frame with a simple and efficient design, to schedule the transmission times for multiple users. Simulation results demonstrate that the proposed scheme offers an approximately 6 dB gain in signal-to-noise ratio (SNR) at a bit error rate (BER) of $3{\times}10^{-5}$, as compared to conventional MU single-input single-output (SISO) systems. Moreover, a data rate of 66.7 Mbps/user at a BER of $10^{-3}$ is achieved for 10 users in indoor VLC environments.

• 제어로봇시스템학회논문지
• /
• 제21권11호
• /
• pp.1076-1080
• /
• 2015

An inventory control system was developed for a distribution system consisting of a single multiproduct warehouse serving a set of customers and purchasing products from multiple vendors. Purchase orders requesting multiple products are delivered to the warehouse in a process. The receipt of customer orders by the warehouse proceeded in order intervals and in order quantities that are subject to random fluctuations. The objective of warehouse operation is to minimize the total cost while maintaining inventory levels within the warehouse capacity by adjusting the purchase order intervals and quantities. An adaptive model predictive control algorithm was developed using a periodic square wave model to represent the material flows. The adaptive concept incorporated a stabilized minimum variance control-type input calculation coupled with input/output stream parameter predictions. The effectiveness of the scheme was demonstrated using simulations.

• Advances in aircraft and spacecraft science
• /
• 제1권4호
• /
• pp.427-441
• /
• 2014

Orbit-raising is an important step to place spacecraft from parking orbits into working orbits. Attitude control system design is crucial in the success of orbit-raising. Several text books have discussed this design and focused mainly on the traditional methods based on single-input single-output (SISO) transfer function models. These models are not good representations for many orbit-raising control systems which have multiple thrusters and each thruster has impact on the attitude defined by all outputs. Only one published article is known to use a more suitable multi-input multi-output (MIMO) Euler angle model in spacecraft orbit-raising attitude control system design. In this paper, a quaternion based MIMO model for the orbit-raising attitude control system design is proposed. The advantages of using quaternion based model for orbit-raising control system designs are (a) there is no need for mathematical transformations because the attitude measurements are normally given by quaternion, (b) quaternion based model does not depend on rotational sequences, which reduces the chance of human errors, and (c) the singular point of reduced quaternion model is the farthest from the operational point where linearization is performed. We will show that performance of quaternion model based design will be as good as the performance of Euler angle model based design for orbit-raising problem.

• Journal of Communications and Networks
• /
• 제17권3호
• /
• pp.241-246
• /
• 2015

In this paper, we consider a relaying system which employs a single relay in a wireless network with distributed sources and destinations. Here, all source, destination, and relay nodes are equipped with multiple antennas. For amplify-and-forward relay systems, we confirm the achievable sum rate through a joint multiple source precoders and a single relay filter design. To this end, we propose a new linear processing scheme in terms of maximizing the sum rate performance by applying a blockwise relaying method combined with geometric programming techniques. By allowing the global channel knowledge at the source nodes, we show that this joint design problem is formulated as a standard geometric program, which can guarantees a global optimal value under the modified sum rate criterion. Simulation results show that the proposed blockwise relaying scheme with the joint power allocation method provides substantial sum rate gain compared to the conventional schemes.

• 한국통신학회논문지
• /
• 제39A권10호
• /
• pp.579-584
• /
• 2014

본 논문에서는 패치형 ESPAR(Electronically Steerable Parasitic Array Radiator) 안테나를 이용한 빔 공간 MIMO(beamsapce mulitple input multiple output) 시스템을 제안한다. 기존의 모노폴 ESPAR 안테나의 경우 단일 RF 체인을 갖기 때문에 하드웨어의 비용과 RF회로의 전력 소모를 절감할 수 있는 장점을 가진다. 하지만 공간적 제약이 큰 휴대용 이동기기에 적용하기 문제점이 있다. 따라서 부피를 간소화 시키는 방법으로써 패치형 ESPAR 안테나를 설계하고 단일 RF 체인으로 MIMO 기술이 가능한 빔 공간 MIMO 시스템에서의 성능을 분석한다. 본 논문에서 설계한 패치형 ESPAR 안테나를 통해 빔패턴이 ${\pm}15$도의 앙각의 변화를 가지는 것을 확인하였고, 또한 이 ESPAR 안테나를 사용하여 빔 공간 MIMO 시스템을 구현하고 이 시스템의 BER 성능을 확인하였다.