• The KIPS Transactions:PartC
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• v.12C no.7 s.103
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• pp.1025-1030
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• 2005

Cooperative communications among users in multiple access wireless environments is an efficient way to obtain the powerful benefits of multi-antenna systems without the demand for physical arrays. This paper proposes a solution to optimize the weights of partnering users' signals for the minimum error probability at the output of maximum likelihood (ML) detector under the transmit power constraints by taking advantage of channel state information (CSI) feedback from the receiver to the transmitter. Simulation programs are also established to evaluate the performance of the system under flat Rayleigh fading channel plus AWGN (Additive White Gaussian Noise).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.12
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• pp.873-875
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• 2014

In this paper we describe an asynchronous MAC protocol with receiver-initiated duty cycling for energy-efficiency in wireless sensor networks(WSN). Legacy asynchronous MAC protocols, X-MAC and PW-MAC, has weaknesses which generates too many control packets and has data collision problem between multiple transmitters, respectively. Therefore, we propose a receiver-initiated asynchronous MAC protocol which generates control packets from transmitter to complement these disadvantages. Compared to the prior asynchronous duty cycling approaches of X-MAC and PW-MAC, the proposed protocol shows a improvement in energy-efficiency, throughput and latency from simulation results.

• Transactions on Electrical and Electronic Materials
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• v.11 no.5
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• pp.238-241
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• 2010

The purpose of this study is to solve the problems of radio frequency bandwidth frequency depletion, confusion possibilities, and security that are in current wireless communications systems, and to confirm the possibility of applying those solutions for the next generation network. To solve the problems of the current wireless communications system, a visible light communications system for power line communication (PLC) via 8-bit microcontroller is created and the capacity is analyzed. The exclusive PLC chip APLC-485MA, an 8-bit ATmega16 microcontroller, high brightness 5pi light emitting diodes (LEDs), and the LLS08-A1 visible light-receiving sensor were used for the transmitter and receiver. The performance was analyzed using a designed program and an oscilloscope. The voltage change was measured as a function of distance from 10-50 cm. Blue LEDs showed the best performance among the measured LED types, with 0.47 V of voltage loss, but for a distance over 50 cm, precise data was not easy to obtain due to the weak light. To overcome these types of problems, specific values such as the changing conditions and efficiency value relevant to the light emitting parts and the visible light-receiving sensor should be calculated, and continuous study and improvements should also be realized for better communication conditions.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.3
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• pp.79-84
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• 2011

In this paper, we analyzed performance of vehicle detection for ITS (Intelligent Transport System) applications. We simulated the vehicle detection at Hi-Pass System is based on DSRC (Dedicated Short Range Communication). DSRC is a wireless network using ITS, including GPS (Global Positioning System) satellites in conjunction with the national transportation system. The system performance is evaluated in terms of bit error probability. In the simulation, the vehicle speed is set at 60 km/h and carrier frequency is 5.8 GHz. Wireless channel is modeled as the Rician fading channel. In the transmitter, the ASK (amplitude shift keying) modulation scheme is applied. From simulation results, we confirmed that performance of applied Alamouti scheme is better than other systems.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.5
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• pp.1-10
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• 1999

A low power concumption 2.4 GHz one-chip transceiver MMIC was designed and fabricated using $1.0\mu\textrm{m}$ ion-implantation MESFET process and packaged on a 24 lead SSOP. In the transmitter mode, it revealed conversion gain of 7.5 dB, output IP3 of -3.5 dBm, and noise figure of 3.9 dB at 2.44 GHz with 3.9 mA current consumption. In the receiver mode, it revealed voltage sensitivity of 6.5 mV/$\mu\$W with 2 .0 mA current consumption. Comparing the fabricated MMIC with the results of MMICs reported elsewhere, it was shown that the fabricated MMIC had good performance. The low power consumption 2.4 GHz transceiver MMIC is expected to be used for various applications such as wireless local area networks, wireless local loops and RFID tags in ISM-band.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.3
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• pp.80-85
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• 2008

Capsule endoscopes generally use primary cells as a power source due to its limited space. However, the primary cells have several limitations such as high cost, limited power and no reuse. To solve these problems, a new wireless energy transmission method is proposed. The proposed approach uses air-gap transformer concepts and LC resonance to transmit energy from transmitter(primary side) to capsule endoscopes(secondary side). The ferrite core with 3-axis winding is used to increase energy transfer efficiency regardless of direction and location. The experimental results show that the proposed method stably supplies 30mW power to secondary circuit.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.2
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• pp.703-722
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• 2016

Passive wireless devices have increasing civilian and military applications, especially in the scenario with wearable devices and Internet of Things. In this paper, we study indoor localization of a target equipped with radio-frequency identification (RFID) device in ultra-wideband (UWB) wireless networks. With known room layout, deterministic multipath components, including the line-of-sight (LOS) signal and the reflected signals via multipath propagation, are employed to locate the target with one transmitter and a single inaccurate receiver. A factor graph corresponding to the joint posterior position distribution of target and receiver is constructed. However, due to the mixed distribution in the factor node of likelihood function, the expressions of messages are intractable by directly applying belief propagation on factor graph. To this end, we approximate the messages by Gaussian distribution via minimizing the Kullback-Leibler divergence (KLD) between them. Accordingly, a parametric message passing algorithm for indoor passive localization is derived, in which only the means and variances of Gaussian distributions have to be updated. Performance of the proposed algorithm and the impact of critical parameters are evaluated by Monte Carlo simulations, which demonstrate the superior performance in localization accuracy and the robustness to the statistics of multipath channels.

• Journal of electromagnetic engineering and science
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• v.11 no.1
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• pp.34-41
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• 2011

This paper proposes a systematic design for a precoding codebook for a transmit-ing space-division multiple access (TN-SDMA) sharing spectrum with existing fixed wireless service (FWS). Based on an estimated direction angle of a victim FWS system, an interfering transmitter adaptively constructs a codebook, forming a transmit in the direction angle, while satisfying orthogonal beamforming constraints. Sum throughput results indicate that the throughput loss of TN-SDMA relative to a practical SDMA, called per user unitary and rate control ($PU^2RC$), is lower at larger number of transmission antennas, lower signal-to-noise ratio, or a smaller number of users. In particular, a small loss (12% throughput loss) is provided for practical system parameters. Spectrum sharing results confirm that TNSDMA efficiently shares spectrum with FWS systems by reducing protection distance to more than 66 %. Although a TN-SDMA system always has lower throughput compared to $PU^2RC$ in non-coexistence scenarios; it offers an intriguing opportunity to re-use a spectrum already allocated to an FWS.

• The KIPS Transactions:PartC
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• v.13C no.3 s.106
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• pp.317-322
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• 2006

This paper presents an efficient user-cooperation protocol associated with cyclic coding for WSNs (Wireless Sensor Networks) using LEACH(Low-Energy Adaptive Clustering Hierarchy). Since the proposed user-cooperation requires no CSI(Channel State Information) at both transmitter and receiver, and encoding and decoding of cyclic codes are simple, the processing complexity of sensor nodes is significantly reduced. Simulation results reveal such a combination can save the network energy up to 10dB over single-hop transmission at BER of $10^{-4}$.

• Journal of Communications and Networks
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• v.17 no.6
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• pp.634-646
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• 2015

Assuming perfect channel state information (CSI) at the transmitter and receiver, the optimization problem of maximizing the minimum Euclidean distance between two received signals by a linear precoder is considered for multiple-input multiple-output (MIMO) systems with arbitrary dimensions and arbitraryary quadrature amplitude modulation (QAM) input. A general precoding framework is first presented based on the Gram matrix, which is shown for 2-dimensional (2-D) and 3-dimensional (3-D) MIMO systems when employing the ellipse expanding method (EEM). An extended precoder for high-dimensional MIMO system is proposed following the precoding framework, where the Gram matrix for high-dimensional precoding matrix can be generated through those chosen from 2-D and 3-D results in association with a permutation matrix. A complexity-reduced maximum likelihood detector is also obtained according to the special structure of the proposed precoder. The analytical and numerical results indicate that the proposed precoder outperforms the other precoding schemes in terms of both minimum distance and bit error rate (BER).