• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.2
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• pp.565-581
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• 2019

This paper investigates the wireless powered two way relay network (WPTWRN), where two single-antenna users and one single-antenna relay firstly harvest energy from signals emitted by a multi-antenna power beacon (PB) and then two users exchange information with the help of the relay by using their harvested energies. In order to improve the energy transfer efficiency, energy beamforming at the PB is deployed. For such a network, to explore the performance limit of the presented WPTWRN, an optimization problem is formulated to obtain the achievable rate region bounds by jointly optimizing the time allocation and energy beamforming design. As the optimization problem is non-convex, it is first transformed to be a convex problem by using variable substitutions and semidefinite relaxation (SDR) and then solve it efficiently. It is proved that the proposed method achieves the global optimum. Simulation results show that the achievable rate region of the presented WPTWRN architecture outperforms that of wireless powered one way relay network architecture. Results also show that the relay location has significant impact on achievable rate region of the WPTWRN.

• Journal of Communications and Networks
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• v.14 no.6
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• pp.619-628
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• 2012

The ZigBee network has been considered to monitor electricity usage of home appliances in the smart grid network. ZigBee, however, may suffer from a coexistence problem with wireless local area network (WLAN). In this paper, to resolve the coexistence problem between ZigBee network and WLAN, we propose a new protocol constructing a cognitive smart grid network for supporting monitoring of home appliances. In the proposed protocol, home appliances first estimates the transmission timing and channel information of WLAN by reading request to send/clear to send (RTS/CTS) frames of WLAN. Next, based on the estimated information, home appliances transmit a data at the same time as WLAN transmission. To manage the interference between WLAN and smart grid network, we propose a cognitive beamforming algorithm. The beamforming algorithm is designed to guaranteeing zero interference to WLAN while satisfying a required rate for smart metering. We also propose an energy efficient rate adaptation algorithm. By slowing down the transmission rate while satisfying an imperceptible impact of quality of service (QoS) of the receiver, the home appliance can significantly save transmit power. Numerical results show that the proposed multiple antenna technique provides reliable communications for smart metering with reduced power comparing to the simple transmission technique.

• Journal of the Korea Society of Computer and Information
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• v.16 no.8
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• pp.119-128
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• 2011

This paper introduces design space exploration of many-core processors that meet high performance and low power required by the beamforming algorithm of image signals of mobile ultrasound. For the design space exploration of the many-core processor, we mapped different number of ultrasound image data to each processing element of many-core, and then determined an optimal many-core processor architecture in terms of execution time, energy efficiency and area efficiency. Experimental results indicate that PE=4096 and 1024 provide the highest energy efficiency and area efficiency, respectively. In addition, PE=4096 achieves 46x and 10x better than TI DSP C6416, which is widely used for ultrasound image devices, in terms of energy efficiency and area efficiency, respectively.

• ETRI Journal
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• v.38 no.5
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• pp.941-951
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• 2016

In this paper, cognitive radio and simultaneous wireless information and power transfer (SWIPT) are effectively combined to design a spectrum-efficient and energy-efficient transmission paradigm. Specifically, a novel SWIPT-based primary-secondary cooperation model is proposed to increase the transmission rate of energy/spectrum constrained users. In the proposed model, a multi-antenna secondary user conducts simultaneous energy harvesting and information forwarding by means of power splitting (PS), and tries to maximize its own transmission rate under the premise of successfully assisting the data delivery of the primary user. After the problem formulation, joint power splitting and beamforming optimization algorithms for decode-and-forward and amplify-and-forward modes are presented, in which we obtain the optimal PS factor and beamforming vectors using a golden search method and dual methods. Simulation results show that the proposed SWIPTbased primary-secondary cooperation schemes can obtain a much higher level of performance than that of non-SWIPT cooperation and non-cooperation schemes.

• The KIPS Transactions:PartA
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• v.18A no.2
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• pp.45-52
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• 2011

In the past, a patient went to the room where an ultrasound image diagnosis device was set, and then he or she was examined by a doctor. However, currently a doctor can go and examine the patient with a handheld ultrasound device who stays in a room. However, it was implemented with only fundamental functions, and can not meet the high performance required by the focusing algorithm of ultrasound beam which determines the quality of ultrasound image. In addition, low energy consumption was satisfied for the mobile ultrasound device. To satisfy these requirements, this paper proposes a high-performance and low-power single instruction, multiple data (SIMD) based multi-core processor that supports a representative beamforming algorithm out of several focusing methods of mobile ultrasound image signals. The proposed SIMD multi-core processor, which consists of 16 processing elements (PEs), satisfies the high-performance required by the beamforming algorithm by exploiting considerable data-level parallelism inherent in the echo image data of ultrasound. Experimental results showed that the proposed multi-core processor outperforms a commercial high-performance processor, TI DSP C6416, in terms of execution time (15.8 times better), energy efficiency (6.9 times better), and area efficiency (10 times better).

• Journal of Satellite, Information and Communications
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• v.6 no.1
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• pp.57-62
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• 2011

The VLC (visible light communication) system is communication technology using visible rays (RGB) that come out in LED device. It is energy curtailment effect and possible in ubiquitous network service applications. Also, VLC system has the above advantage about that the communication throughout the whole room is enabled by high power lighting and lighting equipment with white colored LED which are easy to install and have good outward appearance. However, the signal detection performance for the receiver near the network of transmitter boundary is severely degraded and the transmission efficiency decreased due to the influence of the interference signal from the adjacent networks. In this paper, we propose an interference mitigation method with optical beamforming in VLC systems, and evaluate the reception performance. For the system BER, the proposed optical beamforming transmission demonstrates the performance enhancement compared to the not using the optical beamforming scheme, and up to about 5~6dB SNR performance gain is achieved.

• Journal of Satellite, Information and Communications
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• v.7 no.3
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• pp.63-68
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• 2012

The VLC (visible light communication) system is communication technology using visible rays (RGB) that come out in LED device. It is energy curtailment effect and possible in ubiquitous network service applications. Also, VLC system has the above advantage about that the communication throughout the whole room is enabled by high power lighting and lighting equipment with white colored LED which are easy to install and have good outward appearance. However, the signal detection performance for the receiver near the network of transmitter boundary is severely degraded and the transmission efficiency decreased due to the influence of the interference signal from the adjacent networks. In this paper, we propose an interference mitigation method with optical relay and optical beamforming scheme in VLC systems, and evaluate the reception performance. For the system BER, the proposed system demonstrates the performance enhancement compared to the not using the optical relay and optical beamforming scheme, and SNR performance gain and higher channel capacity is achieved.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.4
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• pp.10-15
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• 2017

Feedback burden of a full-digital energy beamforming, which is known as the optimal precoding scheme for radio frequency (RF) energy transfer, is huge because it uses a vector quantization for a channel feedback. To reduce the feedback burden, we consider a beam steering based wireless energy transfer, which uses a scalar quantization. Researches related to the beam steering based wireless energy transfer have been studied in special channel model with an assumption of full channel state information at the transmitter. In this paper, we analyze the beam steering scheme compared with the full-digital energy beamforming for practical channel models with channel estimation errors. According to characteristics of the millimeter wave channel, the number of antennas of the base station and the user, the distance between them, and channel estimation errors, we simulate the performance of the beam steering scheme and analyze reasons why.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.704-705
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• 2014

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.2
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• pp.219-226
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• 2013

Distributed multi-hop relay scheme to reduce delay-constrained outage probability for broadcast network is proposed. We consider multi-hop relay scheme, which is similar to distributed beamforming, where multiple nodes simultaneously relay packets, and we propose channel access control and power control for relaying nodes to satisfy energy constraint. Compared with flooding which is multi-hop relay scheme used for ZigBee, the proposed scheme is better in terms of outage probability and average reception throughput.