• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12B
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• pp.1058-1067
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• 2006

In this paper, we propose a inband/outband broadcast method for hidden incumbent system detection of medium access control layer for wireless regional area network systems using cognitive radio technology. Through some extra channels that are not currently used, a short message is broadcasted. The message allows CPE detecting an appearance of incumbent system to send sensing report to CR BS. For the hidden incumbent system report message, the BS needs a process or method for allocation of upstream resource to CPEs. And transmitting multiple out-band signals has a possibility to collide with out-band signals of other co-located WRAN BSs. To avoid out-band signal collision, BSs randomly select it out-band signal broadcasting time within the pre-defined explicit out-band signaling, period. And fractional Bandwidth Usage allows WRAN BSs to efficiently use bandwidth.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.2 s.58
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• pp.38-49
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• 2006

In order to increase the spectrum efficiency, recently, there is the number of studies for CR technology. For instance, IEEE 802.22 WRAN(Wireless Regional Area Network) WG considered the CR technology as a solution of WRAN system to serve the high speed internet service(1.5 Mbps down stream and 384 kbps up stream) in 100 km overall coverage and 54 MHz-746 MHz band. Basically, in MAC point of view, the WRAN system have been standardizing based on the IEEE 802.16 MAC layer features such as Data transmission method, QoS provision and Bandwidth request schemes. Additionally, the WRAN system further include CR nature functions such as incumbent user protection, self coexistence which would be importantly considered. Also, the inherent WRAN functions are added such as channel bonding and fractional bandwidth usage. This paper mainly explained frame structure, IU protection, self coexistence which are key functions of WRAN system. Finally, in this paper, we expressed a prospect of IEEE 802.22 WRAN standardization.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.4
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• pp.1-8
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• 2011

In this paper, a microstrip bandpass filter(BPF) with 3 dB bandwidth of more than 50 % at center frequency of 30 GHz was implemented. The implemented BPF is to be used as ASK(Amplitude Shift Keying) transmission and reception filters in IF band for THz transmitter and receiver capable of 10 Gb/s wireless data transmission. The microstrip BPF with ultra-wideband characteristics was implemented using a stepped-impedance lowpass filter(LPF) and a composite quarter-wave short stubs where the LPF is functioning as attenuating the upper stopband and quarter-wave short stubs is functioning as attenuating the lower stopband. The measured results are as follows; the insertion loss is 0.65 dB at 30 GHz, the stopband characteristics are -10 dB and -16 dB at 10 GHz and 50 GHz, respectively, and the passband flatness is ${\pm}0.5$ dB at 20~40 GHz.

• Journal of Digital Contents Society
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• v.10 no.2
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• pp.357-365
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• 2009

To effectively exploit the underlying network bandwidth while maximizing user perceivable QoS, mandatory to make proper estimation on packet loss and queuing delay of the underling network. This issue is further emphasized in wireless network environment where network bandwidth is scarce resource. In this work, we focus our effort on developing performance model for wireless network. We collect packet trace from actually wireless network environment. We find that packet count process and bandwidth process in wireless environment exhibits long range property. We extract key performance parameters of the underlying network traffic. We develop an analytical model for buffer overflow probability and waiting time. We obtain the tail probability of the queueing system using Fractional Brown Motion (FBM). We represent average queuing delay from queue length model. Through our study based upon empirical data, it is found that our performance model well represent the physical characteristics of the IEEE 802.11b network traffic.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.5
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• pp.592-597
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• 2012

In this paper, a new small chip antenna for Wi-Fi application of the mobile handset is proposed. To miniaturize the chip antenna, the proposed antenna is designed to have the backside ground. The proposed antenna has S-shaped structure, which is designed on the LCP(Liquid Crystal Polymer) with ${\varepsilon}_r$=3.5. The size of the proposed antenna is $6.0mm{\times}2.5mm{\times}1.2mm$. The measured impedance bandwidth under a voltage standing wave ratio (VSWR) of 2 was 300 MHz(fractional bandwidth: 12.2 % 2.3~2.6 GHz), and peak gain is 1.42 dBi. The proposed antenna was designed using CST Microwave Studio commercial software tool. And the fabricated antenna is measured using a network analyzer and in anechoic chamber.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.3
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• pp.342-348
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• 2015

This paper presents a 1.9-GHz digital ${{\Delta}{\Sigma}}$ fractional-N PLL with a finite impulse response (FIR) filter embedded for noise suppression. The proposed digital implementation of FIR provides a simple method of increasing the number of taps without complicated calculation for gain matching. This work demonstrates 32 tap FIR filtering for the first time and successfully filtered the in-band phase noise generated from delta-sigma modulator (DSM). Design considerations are also addressed to find the optimum number of taps when the resolution of time-to-digital converter (TDC) is given. The PLL, fabricated in $0.11-{\mu}m$ CMOS, achieves a well-regulated in-band phase noise of less than -100 dBc/Hz for the entire range inside the bandwidth of 3 MHz. Compared with the conventional dual-modulus division, the proposed PLL shows an overall noise suppression of about 15dB both at in-band and out-of-band region.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2389-2391
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• 2005

In this paper, a compact S type resonator is presented, where the proposed resonator is surface micromachined over transmission lines or other resonators, in order to obtain a wide range of possible electromagnetic couplings. The structure has been applied in two compact, bandstop and bandpass filters with moderate fractional bandwidths (FBW) of 20% and 25% respectively. The bandstop filter presented, was designed by the combination of two design methods in order to obtain the proposed fractional bandwidth, where traditionally, coupled resonator bandstop filters have been used for narrow stopbands. The bandpass filter illustrates the use of the proposed suspended resonator structure to obtain a wide range of electric type coupling coefficients, and external quality factors for the filter. This paper describes the design methodology, concepts and fabrication method proposed for the design of these filters.

• The KIPS Transactions:PartC
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• v.11C no.3
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• pp.395-400
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• 2004

Being aware of growing needs for wireless communication led to the development of UWB systems, this study proposed an impulse for single band UWB systems which does not count a carrier; analyzed the characteristics and the problems of pulses suggested by the existing poise of the Un system; finally, proposed TDMG(Time Delay Multiple Gaussian) pulse that generates signals of UWB without attenuation of pulse width. The hardware structure of the TDMC pulse for the single band UWB system was modelled after describing the pulse in a mathematical method in an attempt to compare with performances of the existing pulses through computer simulation. The outcome of the test unveiled the fact that each center frequency of the TDMG pulse rose approximately 1GHz, and also each l0dB fractional bandwidth of the TDMG pulse was widened over 1GHz. In the case of derivative, center frequencies of the TDMG pulse rose over 1GHz each. As a consequence, the TDMG pulse appeared to have better quality frequency, satisfying the characteristics of spectrum and the band of frequency recommended by the FCC and decreasing interference with other wireless communication systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.5
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• pp.583-591
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• 2012

In this paper, using a folded parasitic patch, a hybrid metamaterial antenna having the enhanced bandwidth is presented. To obtain a broad bandwidth of the antenna, a zeroth-order resonance(ZOR) mode of a mushroom antenna and a $TM_{010}$ mode of a conventional patch antenna are combined. By employing an etched rectangular hole and a folded parasitic patch in the conventional patch antenna, a resonance frequency of the $TM_{010}$ mode can be down-shifted toward that of the ZOR mode without changing the size of the antenna. Therefore, the proposed antenna has broad bandwidth which ranges from the ZOR mode to the $TM_{010}$ mode. As a result, a fractional bandwidth of the proposed antenna is measured as 12 % and a radiation efficiency is above 75 % in whole band.

• Journal of Internet Computing and Services
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• v.19 no.1
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• pp.11-17
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• 2018

In this paper, we propose a novel frequency reuse method using the fractional frequency reuse (FFR) for enterprise femtocell networks (EFNs) in which a lot of femtocell base stations (fBSs) are deployed in a buinding, e.g., business companies, department stores, etc, and evaluate the system performance for the downlink of EFNs. First, we introduce the concept of the split reuse method to allocate the frequency bandwidth with considering the interference between the macrocell and femtocell. Then, we propose the resource allocation with the FFR for fBSs of EFNs to reduce the interference and increase the system capacity. Through simulations, we show that the proposed FFR method outperforms a traditional resource allocation method with frequency reuse factor 4 in terms of the mean fUE capacity, total EFN capacity, and outage probability.