• The KIPS Transactions:PartC
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• 제18C권4호
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• pp.251-254
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• 2011

In a WLAN, the data reception rate of a user station depends not only on the received signal strength (RSS) from an AP (Access Point) but also on the contention level of the AP. However, since only the RSSs measured at the physical layer have been used for a station to select an AP to associate with, the station may not satisfy the minimum quality requirements necessary for a seamless IPTV service. Thus, in this paper, we propose an AP selection method to support quality requirements of the IPTV service in a wireless LAN without modifying the IEEE 802.11 standard. A user station keeps monitoring a contention level of APs around it and a quality of an ongoing IPTV service. If the quality deteriorates below a threshold, the station reassociates with another AP having the least load so that the ongoing IPTV program is played without disruption.

• Journal of Advanced Navigation Technology
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• 제23권5호
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• pp.373-379
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• 2019

AeroMACS spectrum is a national resource internationally allocated by ITU at WRC-07. AeroMACS is an airport broadband mobile communication infrastructure based on WiMAX-based IEEE 802.16e that enables real-time video, graphics, voice, and high-speed data transmission. With the approval of ICAO's development technology standards in 2008, 50 airports in 11 countries have already completed the testing of D-TAXI or A-SMGCS technology using the AeroMACS infrastructure in 2019, starting in the United States in 2009. With many advantages in safety and convenience in terrestrial telecommunications operations, the system is becoming an area of performance improvement for airport operations in accordance with ICAO's ASBU plan. This paper examines the current status of domestic development of AeroMACS and lists service areas applicable to airlines and operators. It also seeks to promote safe and efficient next-generation airport mobile communication system services by presenting feasible partners management in the mobile area and use of aircraft communication systems for active technology development.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제44권3호
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• pp.92-97
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• 2007

Switching mode amplifiers have been studied widely for use at microwave frequency range, and the class E amplifier which is a type of switching mode amplifier offers very high efficiency approaching 100%. In this paper, 2.4GHz microwave class E amplifier with 66% power added efficiency (PAE) and 17.6dBm output has been linearized for use at wireless LAN transmitter, and digital predistortion technique with look up table is applied. With -3dBm input power of wireless LAN, measured output spectrum can meet the required IEEE 802.11g standard spectrum mask, and the digital predistortion output spectrum has been improved by 5dB of ACPR at 20MHz offset from center frequency.

• Journal of Satellite, Information and Communications
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• 제11권3호
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• pp.133-137
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• 2016

Millimeter wave wireless communication systems, especially those targeting indoor high rate data transfer, have a strong requirement for high quality wireless link. Unfortunately, in this frequency band, the electromagnetic wave has to sustain the high propagation loss caused by the smaller wavelengths. In this scenario, beamforming technique, which enhances the link quality by focusing the radiation power on a direction, becomes one of the most important techniques in millimeter wave band wireless communication. In recent year, there been conducted many research on beamforming to improve the performance of wireless system. In this paper, we evaluate the performance of a simplified codebook-based beamforming scheme which is based on multiple-procedure and three-state beam selection. The simplified scheme significantly reduces beamforming setup time, comparing to the exhaustive searching, two-level searching adopted in IEEE 802.15.3c standard, and also conventional multi-level scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제32권11C호
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• pp.1087-1094
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• 2007

In this paper, we propose a new peak-to-average power ratio (PAPR) reduction scheme of orthogonal frequency division multiplexing (OFDM) system, called a modified selected mapping (SLM) scheme, which considerably reduces the computational complexity with keeping the similar PAPR reduction performance compared with the conventional SLM scheme. The proposed scheme is analytically and numerically evaluated for the OFDM system specified in the IEEE 802.16 standard. For the OFDM system with 2048 subcarriers, the proposed scheme with 4 binary phase sequences can reduce the complex multiplications by 63.5% with the similar PAPR reduction compared with the SLM scheme with 16 binary phase sequences.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제44권4호
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• pp.28-39
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• 2007

This paper presents a programmable RF DFT (Radio Frequency Design-for-Testability) circuit for low noise amplifiers. We have developed a new on-chip RF DFT circuit that measures RF parameters of low noise amplifier (LNA) using only DC measurements [1, 2]. This circuit is extremely useful for today's RFIC devices in a complete RF transceiver environment. The DFT circuit contains test amplifier with programmable capacitor banks and RF peak detectors. The test circuit utilizes output DC voltage measurements and these measured values are translated into the LNA specifications such as input impedance and gain using the mathematical equations. Our on-chip DFT circuit can be self programmed for 1.8GHz, 2.4GHz and 5.25GHz low noise amplifiers for GSM, Bluetooth and IEEE802.11g standards. The circuit is simple and inexpensive.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제45권5호
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• pp.1-11
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• 2008

Wireless Sensor Networks is applied to improvement of life convenience or service like U-City as well as environment pollution, tunnel and structural health monitoring, storm, and earthquake diagnostic system. To increase the usability of sensor data and applicability, mobile devices and their facilities allow the applications of sensor networks to give mobile users and actuators the results of event detection at anytime and anywhere. In this paper, we present MUSNEMO(Multi-sensor centric Ubiquitous Smart sensor NEtwork using Mobile devices) developed system for providing more efficient and valuable information services with a variety of mobile devices and network camera integrated to WSN. Our system is performed based on IEEE 802.15.4 protocol stack. To validate system usability, we built sensor network environments where were equipped with five application sensors such magnetic, photodiode, microphone, motion and vibration. We also built and tested proposed MUSNEMO to provide a novel model for event detection systems with mobile framework.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제18권3호
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• pp.257-264
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• 2007

In this paper, we have designed and fabricated a wide-band and high gain antenna which can integrate a standard of IEEE 802.1la$(5.15\sim5.25\;GHz,\;5.25\sim5.35\;GHz,\;5.725\sim5.825\;GHz)$. We inserted a parallel dual slot into a rectangular patch to have wide-band, and we offset an element of capacitance from the slot by using coaxial probe feeding method. We also designed a converter of $\lambda_g/4$ impedance with taper type line so that wide-band impedance can be matched easily. We finally designed structure with $2\times2$ array in order to improve the antenna gain, and the final fabricated antenna could have a good return loss(Return loss$\leq$-10 dB) and a high gain(over 13 dBi) at the range of $5.01\sim5.95\;GHz(B/W\doteqdot940\;MHz)$.

• Proceedings of the Korean Information Science Society Conference
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• 한국정보과학회 2007년도 한국컴퓨터종합학술대회논문집 Vol.34 No.1 (D)
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• pp.238-242
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• 2007

무선이동기기의 에너지 소모를 줄이기 위해서는 무선인터페이스의 전력소모를 최대한 줄이는 것이 중요하다. 대표적인 무선통신인 IEEE 802.11 표준에서는 무선인터페이스를 수면모드로 전환하는 전력절약모드(PSM, Power Save Mode)를 정의하고 있다 그러나 수면모드로 동작하는 도중에는 데이터를 수신할 수 없으므로 전력절약과 전송지연 사이에서 조정(trade-off)을 하여야 한다. HTTP와 같이 요청-응답을 기본으로 하는 통신 응용에서는 요청 발생 후 응답이 도착할 때까지 걸리는 시간을 노드의 수면시간에 반영하면 데이터의 수신이 지연되는 문제를 완화하면서 전력절약을 할 수 있으며, 기존 연구들도 이에 착안하는 기법을 제안하고 있다. 그러나 기존 연구들은 HTTP통신이 다중적으로 발생하면 그 효과는 사라지게 된다. 본 연구에서는 기존에 제안된 기법이 갖는 문제점을 분석하고 이를 완화하기위해 응답시간 지연비율을 적용한 지연수면(Delayed Sleep) 스케줄링 기법을 제안하며 시뮬레이션을 통해 이를 검증하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 한국해양정보통신학회 2007년도 추계종합학술대회
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• pp.958-961
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• 2007

Recently, research and deployment have been very active on wireless mesh technologies. Wireless mesh networks extends the coverage of the WLAN easily and economically. Although existing protocols developed for MANET and WSN can be used for wireless mesh WLANs, considerable amount of research are still required, because they exhibit poor performance, when applied as they are, due to a few critically different requirements This paper examine research issues on physical and link layers of WLANs considering those requirements.