• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12C
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• pp.1197-1207
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• 2009

Orthogonal Frequency Division Multiple Access (OFDMA) is widely used as a multiple access technique for next generation mobile communication systems, however, its main drawback is the high peak-to-average ratio (PAPR). Thus for the uplink case where the transmit power is strictly limited due to the battery life of mobile units, single carrier frequency division multiple access (SC-FDMA) with low PAPR is preferred to OFDMA method. In this paper, we propose a method to improve the performance of SC-FDMA using frequency domain MMSE equalization. The proposed improved log-likelihood ratio (LLR) generation method exploits both the diversity characteristic of channels and the reciprocity that is obtained from the received signals. The complexity of the proposed method is analyzed and its performance gain is demonstrated via a set of computer simulations.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.422-423
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• 2010

직렬 연결된 배터리는 각 셀의 내부 화학적 특성 차이로 인해 동일 전류로 충전 및 방전 과정을 진행하여도 셀 간에 미세한 전압 차이가 발생한다. 이러한 셀 간 전압 불균형은 배터리 셀에 해로운 영향을 끼치게 되는데, 2차 전지의 경우 배터리 용량의 변화를 야기한다. 이러한 문제를 해결하기 위해서 배터리 운용 범위를 제한하는 보호회로가 있지만 보호회로는 직렬 연결된 배터리 셀 중 가장 전압이 높거나 가장 낮은 셀을 기준으로 충전과 방전 사이클을 종료시키므로 배터리 팩의 용량을 최대한으로 사용하지 못하게 하는 문제를 발생시킨다. 배터리 균등화 회로는 셀 간의 전압 차이를 줄여 배터리의 최대 용량을 사용하고자 하는 목적을 가진다. 저항을 기반으로 하는 수동적인 방법과는 달리 스위칭 소자를 이용하는 능동적인 방법에서는 스위칭으로 인해 입출력 전압 변동이 발생하여 컨버터 내부에 흐르는 전류가 수시로 변하는 문제가 생긴다. 위 문제를 해결하기 위한 방법으로 본 논문에서는 배터리 균등화 회로에 전하 제어(Charge control)기법을 제안하고, 그에 따른 회로 설계 요소를 제시한다.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.5
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• pp.393-400
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• 2012

The modularized equalizers normally use additional components among the modules in the long series-connected lithium-ion battery string. In these approaches, the overall systems are heavy, bulky, and high-priced. Furthermore, the losses related to additional components decrease the system efficiency. To avoid these problems, a modularized equalizer, which has no additional components among the modules, is required. This paper proposes a novel control scheme using the magnetizing energy of the multi-winding transformer for the module equalization. In this scheme, the high duty cycle is applied to the module where the voltage is higher than the reference voltage and the low duty cycle is applied to the module where the voltage is lower than the reference voltage. Due to the different duty cycle, more electric charges are transferred from high voltage module to the low voltage module during the turn-off switching interval. Using the proposed control scheme, the equalizer system does not suffer from the size, cost, and loss related to the modularization. The experimental results are provided to verify the effectiveness of the proposed modularized equalizer.

• Journal of Internet of Things and Convergence
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• v.10 no.5
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• pp.53-63
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• 2024

The rapid development of wireless sensor network technology has garnered significant attention from researchers. In extensive distributed networks, these applications often rely on battery power. Given the limited energy capacity of batteries, effective energy management is crucial for improving network performance. Wireless sensor networks consist of numerous sensor nodes, where energy consumption is primarily driven by these nodes. In clustering protocols, certain nodes repeatedly serve as cluster heads, resulting in increased energy consumption compared to other nodes. This energy-balancing algorithm employs pruning techniques to evaluate and analyze a node's position, its frequency of acting as a cluster head, and its remaining energy. Additionally, it includes a dynamic adjustment mechanism for selecting the cluster head node. Experimental results demonstrate that this algorithm extends the operational duration of sensor nodes, thereby effectively prolonging the lifespan of the wireless sensor network.