• 인터넷정보학회논문지
• /
• 제22권1호
• /
• pp.1-11
• /
• 2021

Estimation of distribution algorithm (EDA) is a popular stochastic metaheuristic algorithm. EDA has been widely utilized in various optimization problems. However, it has been shown that the diversity of the population gradually decreases during the iterations, which makes EDA easily lead to premature convergence. This article introduces a hybrid estimation of distribution algorithm (EDA) with differential evolution (DE) based on self-adaptive strategy, namely HEDADE-SA. Firstly, an alternative probability model is used in sampling to improve population diversity. Secondly, the proposed algorithm is combined with DE, and a self-adaptive strategy is adopted to improve the convergence speed of the algorithm. Finally, twenty-five benchmark problems are conducted to verify the performance of HEDADE-SA. Experimental results indicate that HEDADE-SA is a feasible and effective algorithm.

• 한국통신학회논문지
• /
• 제31권9A호
• /
• pp.844-855
• /
• 2006

다중 안테나 통신시스템은 서비스 및 채널 환경의 특성에 따라 송수신 다이버시티 기법, 공간 다중화 기법과 빔형성 기법 등을 이용하여 링크의 신뢰성 혹은 시스템 용량을 증가시킨다. 이러한 다중 안테나 통신 시스템은 공간 채널 환경에 민감한 특징을 갖는다. 다이버시티 기법의 경우, 각 링크 간 채널 상관도가 낮을수록 성능이 향상된다. 하지만, 실제 채널 환경은 안테나 간의 상관관계가 많이 존재하며, 이상적인 경우와 실제 성능의 차이가 클 수 있다. 이와 반대로 빔형성 기법의 경우, 채널 상관도가 높은 LoS (Line-of-Sight) 환경에서 가장 좋은 성능을 나타낸다. 이와 같은 공간 채널의 특성을 활용한 공간채널 적응전송기법을 사용할 경우, 최소한의 링크 성능을 유지하며, 전체적인 시스템 성능을 보장할 수 있게 된다. 본 논문에서는 채널의 이러한 특성을 이용하여 링크의 신뢰성이 요구되는 시스템에서 공간 채널 상관도에 따른 다이버시티 기법과 빔형성 기법 간의 적응 송 수신을 통한 성능 향상 방안을 제시한다.

• Journal of Communications and Networks
• /
• 제12권4호
• /
• pp.358-365
• /
• 2010

We develop a low complexity cooperative diversity protocol for low energy adaptive clustering hierarchy (LEACH) based wireless sensor networks. A cross layer approach is used to obtain spatial diversity in the physical layer. In this paper, a simple modification in clustering algorithm of the LEACH protocol is proposed to exploit virtual multiple-input multiple-output (MIMO) based user cooperation. In lieu of selecting a single cluster-head at network layer, we proposed M cluster-heads in each cluster to obtain a diversity order of M in long distance communication. Due to the broadcast nature of wireless transmission, cluster-heads are able to receive data from sensor nodes at the same time. This fact ensures the synchronization required to implement a virtual MIMO based space time block code (STBC) in cluster-head to sink node transmission. An analytical method to evaluate the energy consumption based on BER curve is presented. Analysis and simulation results show that proposed cooperative LEACH protocol can save a huge amount of energy over LEACH protocol with same data rate, bit error rate, delay and bandwidth requirements. Moreover, this proposal can achieve higher order diversity with improved spectral efficiency compared to other virtual MIMO based protocols.

• 한국통신학회논문지
• /
• 제29권7C호
• /
• pp.907-914
• /
• 2004

본 논문에서는 적응 변조 시스템에 수신안테나 교환(switching) 기술을 적용한 방식을 제안하고, 해당 방식이 제공하는 평균 비트 전송 속도를 최대로 하는 안테나 교환 임계값을 유도하였으며, 그에 따른 성능을 도출하였다. 아울러 제안한 시스템의 성능을 단일 안테나를 사용하는 적응 변조 시스템 그리고 안테나 선택 다이버시티(selection diversity)를 사용하는 적응 변조 시스템과 레일레이 페이딩 채널 환경에서 심볼 당 평균 비트 수와 송신 중단 확률 측면에서 비교하였다. 성능 비교 결과 심볼 당 평균 2 비트의 정보를 전달한다고 했을 때 제안한 방식은 단일 안테나를 사용하는 방식에 비해 1.4 dB의 SNR 이득이 있으며, 송신 중단 확률이 0.1일때 제안한 방식은 단일 안테나를 사용하는 방식에 비해 약 6 dB의 SNR 이득을 얻을 수 있음을 알 수 있었다.

• Journal of information and communication convergence engineering
• /
• 제9권2호
• /
• pp.183-186
• /
• 2011

In this work, we consider imperfectness of feedback channels in the adaptive transmission scheme which was previously studied with an assumption of error-free feedback channels. New method of mapping the modulation index into the feedback channel symbols and quantifying feedback error over fading channels are proposed. The presented method and results are expected to offer valuable tools for the system designer to efficiently implement adaptive diversity schemes to compensate for the performance degradation due to feedback error.

• Journal of Communications and Networks
• /
• 제9권2호
• /
• pp.112-117
• /
• 2007

In this paper, we focus on the total transmission power minimization problem for downlink beamforming multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems while ensuring each user's QoS requirement. Although the linear integer programming (LIP) solution we formulate provides the performance upper bound of the margin adaptive (MA) optimization problem, it is hard to be implemented in practice due to its high computational complexity. By regarding each user's equivalent channel gain as approximate independent values and using iterative descent method, we present a heuristic MA resource allocation algorithm. Simulation results show that the proposed algorithm efficiently converges to the local optimum, which is very close to the performance of the optimal LIP solution. Compared with existing space division multiple access (SDMA) OFDM systems with or without adaptive resource allocation, the proposed algorithm achieves significant performance improvement by exploiting the frequency diversity and multi-user diversity in downlink multiple-input single-output (MISO) OFDM systems.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제5권7호
• /
• pp.1293-1310
• /
• 2011

A simple modification of well known Low Energy Adaptive Clustering Hierarchy (LEACH) protocol is proposed to exploit cooperative diversity. Instead of selecting a single cluster-head, we propose M cluster-heads in each cluster to obtain a diversity of order M. The cluster-heads gather data from all the sensor nodes within the cluster using same technique as LEACH. Cluster-heads transmit gathered data cooperatively towards the destination or higher order cluster-head. We propose a code combining based cooperative diversity protocol which is similar to coded cooperation that maximizes the performance of the proposed cooperative LEACH protocol. The implementation of the proposed cooperative strategy is analyzed. We develop the upper bounds on bit error rate (BER) and frame error rate (FER) for our proposal. Space time block codes (STBC) are also a suitable candidate for our proposal. In this paper, we argue that the STBC performs worse than the code combining cooperation.

• ETRI Journal
• /
• 제26권5호
• /
• pp.443-451
• /
• 2004

Since the publication of Alamouti's famous space-time block code, various quasi-orthogonal space-time block codes (QSTBC) for multi-input multi-output (MIMO) fading channels for more than two transmit antennas have been proposed. It has been shown that these codes cannot achieve full diversity at full rate. In this paper, we present a simple feedback scheme for rich scattering (flat Rayleigh fading) MIMO channels that improves the coding gain and diversity of a QSTBC for 2$^n$ (n=3, 4, ${\cdots}$) transmit antennas. The relevant channel state information is sent back from the receiver to the transmitter quantized to one or two bits per code block. In this way, signal transmission with an improved coding gain and diversity near to the maximum diversity order is achieved. Such high diversity can be exploited with either a maximum-likelihood receiver or low-complexity zero-forcing receiver.

• 대한전기학회논문지:시스템및제어부문D
• /
• 제53권4호
• /
• pp.265-276
• /
• 2004

Genetic Algorithm(GA), that is shown stable performance to find an optimal solution, has been used as a method of solving large-scaled optimization problems with complex constraints in various applications. Since it takes so much time to execute a long computation process for iterative evolution and adaptation. In this paper, a hardware-based adaptive GA was proposed to reduce the serious computation time of the evolutionary process and to improve the accuracy of convergence to optimal solution. The proposed GA, based on steady-state model among continuos generation model, performs an adaptive mutation process with consideration of the evolution flow and the population diversity. The drawback of the GA, premature convergence, was solved by the proposed adaptation. The Performance improvement of convergence accuracy for some kinds of problem and condition reached to 5-100% with equivalent convergence speed to high-speed algorithm. The proposed adaptive GAP(Genetic Algorithm Processor) was implemented on FPGA device Xilinx XCV2000E of EHW board for face recognition.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2002년도 ITC-CSCC -3
• /
• pp.1960-1963
• /
• 2002

Transmit diversity schemes we an effective capacity improvement method for down link of wideband code division multiple access (W-CDMA) systems. In this paper, we propose to use transmit antenna subset selection scheme in conjunction with closed loop transmit adaptive array (TxAA). The proposed scheme selects N$\_$s/ optimum antennas among N$\_$${\gamma}$/(>N$\_$s/) transmit antennas in order to maximize diversity gain from selected antennas, and also reduces the cost of RE chains by employing two different types of RF modules fur the selected and the unselected antenna group, respectively. Computer simulation results show performance improvement by the proposed scheme over the conventional TxAA when considering up link control information feedback.