• Journal of Broadcast Engineering
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• v.5 no.2
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• pp.273-280
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• 2000

Channel characteristics between the outdoor transmitter far away from the building and receivers inside the building are explored theoretically using ray tracing technique. In this paper, 29 receivers are located on the single floor of the building to observe the variation of channel properties depending on receiver location. For each receiver, amplitudes and phases of ail the possible rays form the transmitter to the receiver are traced to obtain impulse response. Statistical results for rms delay spread and power delay profiles for representative receiver location are given.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7A
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• pp.727-732
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• 2008

The transmit diversity as well as beamforming can increase the performance of wireless communication systems. It is well known that the requirement for the spacing between the neighboring antennas in transmit diversity and beamforming is contradictive to each other. Therefore it is necessary to find the optimum configuration of multiple antennas for getting the maximum performance under the condition that the total number of antennas at transmitter site and the total power of transmitter are fixed. In this paper, the procedure for finding the optimum configuration of multiple antennas was derived through searching the maximum capacity and BER in the combined system with the transmit diversity (Tx diversity) and beamforming.

• Journal of Sensor Science and Technology
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• v.26 no.6
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• pp.408-413
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• 2017

In this paper, we newly developed a byte-inverted transmission method for flicker-free visible light communication (VLC). The VLC transmitter sends original data in the former half period of the clock, and inverted data and in the latter half period of the clock. The VLC receiver receives the original data in the in the former half period of the clock. In this system, we used 480Hz clock that was generated from the 60Hz power line. The average optical power of the LED array in the transmitter is constant, thus flicker-free, in the observation time longer than the period of the clock that is about 2ms. This period is shorter than the maximum flickering time period (MFTP) of 5ms that is generally considered to be safe. This configuration is very useful in constructing indoor wireless sensor networks using LED light because it is flicker-free and does not require additional transmission channel for clock transmission.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.5
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• pp.173-178
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• 2011

In this paper, we analyze the total performance according to transmit probability of interfering transmitter in hetero systems. We analyze this criteria as a parameter for co-use when hetero systems share the same frequency channels. In order to make an analysis of relationship between transmit probability and performances of two systems. We take into consideration on the case that WLAN is a victim receiver and WiBro is an interfering transmitter. Analyzed coexistence results may be widely applied into the technique developed to get the coexisting condition for wireless devices using many communication protocols in same frequency.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1391-1392
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• 2008

The modulation quality of the I/Q modulator in a wireless transmitter usually affects system performance and it mostly depends on both a nonlinearity and a distortion, from the third order intermodulation(IM3) signal and the imperfection features such as an input amplitude error and a local phase error, respectively. This paper focused on how much the Single Sideband Ratio(SSR), which indicates the signal distortion, changes according to the variation of the imperfection features. Since a desired signal, side band and IM3 signals at the I/Q modulator output are also represented with those power series coefficients and the imperfection features, the effects of the imperfection features on SSR can be clearly analyzed.

• Journal of Communications and Networks
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• v.14 no.2
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• pp.130-139
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• 2012

Energy harvesting has emerged as a powerful technology for complementing current battery-powered communication systems in order to extend their lifetime. In this paper a general framework is introduced for the optimization of communication systems in which the transmitter is able to harvest energy from its environment. Assuming that the energy arrival process is known non-causally at the transmitter, the structure of the optimal transmission scheme, which maximizes the amount of transmitted data by a given deadline, is identified. Our framework includes models with continuous energy arrival as well as battery constraints. A battery that suffers from energy leakage is studied further, and the optimal transmission scheme is characterized for a constant leakage rate.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.1
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• pp.108-122
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• 2014

Massive antenna array is an attractive candidate technique for future broadband wireless communications to acquire high spectrum and energy efficiency. However, such benefits can be realized only when proper channel information is available at the transmitter. Since the amount of the channel information required by the transmitter is large for massive antennas, the feedback is burdensome in practice, especially for frequency division duplex (FDD) systems, and needs normally to be reduced. In this paper a novel channel feedback reduction scheme based on the theory of distributed compressive sensing (DCS) is proposed to apply to massive antenna arrays with spatial correlation, which brings substantially reduced feedback load. Simulation results prove that the novel scheme is better than the channel feedback technique based on traditional compressive sensing (CS) in the aspects of mean square error (MSE), cumulative distributed function (CDF) performance and feedback resources saving.

• ETRI Journal
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• v.43 no.2
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• pp.197-208
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• 2021

Single-carrier frequency division multiple access (SC-FDMA) is currently being used in long-term evolution uplink communications owing to its low peak-to-average power ratio (PAPR). This study proposes a new transceiver design for an SC-FDMA system based on Walsh-Hadamard transform (WHT). The proposed WHT-based SC-FDMA system has low-PAPR and better bit-error rate (BER) performance compared with the conventional SC-FDMA system. The WHT-based SC-FDMA transmitter has the same complexity as that of discrete Fourier transform (DFT)-based transmitter, while the receiver's complexity is higher than that of the DFT-based receiver. The exponential companding technique is used to reduce its PAPR without degrading its BER. Moreover, the performances of different ordered WHT systems have been studied in additive white Gaussian noise and multipath fading environments. The proposed system has been verified experimentally by considering a real-time channel with the help of wireless open-access research platform hardware. The supremacy of the proposed transceiver is demonstrated based on simulated and experimental results.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.314-315
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• 2020

현대의 많은 Internet of Thing (IoT)기기들의 충전방식이 유선 충전이 아닌 무선 충전을 사용함에 따라 다양한 연구들이 활발히 이루어지고 있다. 그 중 공진을 이용한 자기공진 방식의 무선충전 시스템은 전자기유도 방식보다 먼 거리에서 충전이 가능하고 공진부 코일의 중심점을 맞추지 않아도 효율에 큰 차이를 보이지 않는 장점이 있다. 점점 더 무선충전이 가능한 기기들이 많아짐에 따라 소모전력이 큰 기기들의 무선전력전송이 많이 연구되고 있다. 본 논문에서는 2개의 송신코일을 사용하여 기존의 1Transmitter - 1Rectifier (1Tx-1Rx) 방식보다 대용량 전력을 전송할 수 있음을 검증하고자 한다.

• Journal of Korea Society of Industrial Information Systems
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• v.21 no.6
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• pp.31-39
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• 2016

In this paper, we propose a new system for wireless remote control over single-tasking operating systems such as Microsoft's disk operating system(DOS). In order to control a DOS device in a windows operating system, the proposed architecture uses a video transmitter, a virtual network driver, and a wireless keyboard module. Analysis shows that the proposed system, over 15Mbps wireless LAN(802.11n), can transmit at least 10 to 15 video frames, achieves speed up to a maximum of 8Mbps roughly, and is able to satisfy real time processing with respect to key input. Therefore, the proposed system is well suited to a remote control solution based on DOS devices.