• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.1
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• pp.115-125
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• 1998

This paper examined the feasibility of adding a new NGSO/MSS(Non-Geostationary orbit/Mobile satellite service) service link to a frequency band which is already allocated to fixed-service microwave(M/W) system. To achieve this goal, the NGSO/MSS handset performance under the influence of the M/W multiple stations and the influence of handsets on the M/W station were both analyzed. Sharing criterions were also obtained by means of coordination contour in the former case, and handset capacity in the latter case. As the results, it was proven that sharing was feasible only when the vertical distance between handset and trendline was above 4 km except front and back points of M/W antenna bore sight under influence of 9 hops(the distance between hops = 50 km) M/W system on the NGSO/MSS handset, and only when the capacity of handset was below $7.0\times10^{-14}$ handsets/ $m^{2}$ under influence of handsets on the M/W station.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.4B
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• pp.624-628
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• 2000

In this paper, the phenomenon to show in CDMA handset in case of which CDMA handset do not meet Traffic Rho value of IS-98B specifications, which have minimum requirements of CDMA handset about electrical performance is analyzed. This paper proposed method to improve Traffic Rho through improving the matching circuit of TX IF SAW FILTER and deleting noise of LDO(Low Dropout Regulator) to generate 3.OV_TX in TX block. HP8924C(CDMA Mobile Station Tester Set) and HP8595E(Spectrum Analyzer) measures the improved CDMA waveform.

• Proceedings of the IEEK Conference
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• 2003.07c
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• pp.2899-2902
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• 2003

Mobile communication is one of the fastest growing industries in the world and especially in Korea, where we have well over 30 million voice subscribers. Mobile communication now offers variety of data communication services such as wireless internet, multimedia messages, and color graphic displays. Handsets also have grown to accommodate such services, thus with functionalities such as programmable virtual machines that users can download and execute their own programs. In this paper, we have demonstrated a PCS handset monitoring system which can monitor biometry signals - in this case ECG over wireless internet and wireless data network (IS95C) based on programmable virtual machine architecture. The remote client handset receives data signals from a centralized server and processes and displays them in human friendly form in real time. Since every single handset on sales in Korea has programmable virtual machine and more than 10 million handsets are in distribution already, proper applications may have substantial impact on the related fields.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.9
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• pp.899-903
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• 2003

In this paper, a wide band helical antenna for mobile handset using parasitic element effect has been investigated. To obtain the effect of parasitic element, we utilized the cylindrical conductor which is not feed. As thickness of cylindrical conductor is increasing, second and third resonance frequency become abruptly variable. In case of that 4.5mm diameter parasitic element cylindrical conductor is inserted, normal mode helical antenna obtained bandwidth of around 900 MHz on the limit of R. L., - 5 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.9 s.112
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• pp.821-828
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• 2006

In this paper, we investigated SAR(Specific Absorption Rate) value variation by the position and size of the loop-type ground located in a test mobile handset. We carried out simulations on SAR value with loop-type grounds in rear case of a mobile handset, and obtained results showed that different positions and sizes of loop-type grounds had different SAR values. Among investigated positions and sizes of loop-type grounds, the small size case-C showed the best performance; i.e., it showed a decrease efficiency of 8.70 %. And in this case, it showed the highest induced electric-field distribution in the loop-type ground. In the simulation, the folding angle was set to $160^{\circ}$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.9 s.100
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• pp.903-908
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• 2005

In this paper, in order to consider SAR(Specific Absorption Rate) problem at the beginning stage of a handset development, we investigated the Shh value change by using simulation method according to various EMI(Electromagnetic Interference) paint patterns on front case of a handset and folding angles. First, we made some experiments with EMI paint pattern on front case of a handset, and obtained results showed that different patterns of EMI paint had different SAR values. Among the simulation results on SAR value according to EMI paint patterns, the hairpin pattern showed the best performance, i.e. the decrease efficiency of $8.04\%$ and completely removed pattern showed the decrease efficiency of $5.94\%$. Orignal pattern was set as the reference and the folding angle was $150^{\circ}$. Second, simulation was carried out with changing folding angle from $150^{\circ}$ to $140^{\circ}$ and $160^{\circ}$. Simulation results for the modeled handset showed that SAR value was decreased with increasing the folding angle. When the folding angle was $160^{\circ}$ and with original pattern, we got the SAR value of about 1,61 W/kg. When we applied hairpin pattern with the folding angle of $160^{\circ}$, we got the lowest SAR value of about 1.45 W/kg.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.7
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• pp.784-795
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• 2007

In this thesis, the Multi element antenna with wideband and enhanced gain characteristic is proposed to operate at both frequency range from 824 MHz to 896 11Hz for the CDMA and frequency range from 908.5 MHz to 914 MHz for the RFID band. The proposed antenna has tile size of $35{\times}15{\times}5mm^3$ in order to put it in the A model of S company and each element of the proposed antenna is folded to obtain the minimum size. To obtain the antenna with wideband and high gain characteristic, the radiator of the antenna is divided into 4 elements. As a result, bandwidth of the proposed antenna become broader and lower center frequency is appeared due to increased and lengthened current path. Moreover, the enhanced gain characteristic is verified because divided element structure that induct uniform current distribution can get increased antenna efficiency. To attain more uniform current distribution, modified structure of the feeding point that can deliver currents directly is designed. The antenna that alters the feeding structure has higher gain value. Each element is folded to increase the current paths considering the current directions to attain the miniaturization of the antenna. To measure the handset antenna, the handset case must be considered. Even though antenna is designed for predicted characteristic, the resonance frequency is shifted and antenna gain is deteriorated at predicted frequency while antenna is set in the handset case. 1.08 GHz of the resonant frequency is determined after frequency shift from 150 MHz to 200 MHz is confirmed and the maximum gain is measured as 3.1 dBi while antenna is not set in the handset. In case handset case is considered, the experimental results show that the impedance bandwidth for VSWR<2 is from 0.824 GHz to 0.936 GHz(110 MHz). This result appears that the proposed antenna can cover both CDMA and RFID band at once. The measured gain is from -3.4 dBi to -0.5 dBi and it has omni-directional pattern practically.

• Journal of IKEEE
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• v.12 no.4
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• pp.185-195
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• 2008

In this paper, PIFA(Planar Inverted F Antenna) which operates in PCS(Personal Communication System) band is designed and characteristics are investigated. Designed PIFA was installed in three types of handsets, folder, bar, slide, and the performance was evaluated. Head and hand phantom were added to make the most similar environment to real condition of mobile phone use, and influences on antenna performance were analyzed. The simulation results confirm radiation patterns are greatly changed and antenna efficiency is decreased by the effect of human body. Performance variation of the mobile handset antenna was observed as changing the angle between mobile handset and head phantom from $0^{\circ}$ to $2^{\circ},\;4^{\circ}$ to confirm the variation caused by the relative position of mobile handset and head phantom. Directivity was decreased gradually as the antenna goes away from head phantom, and showed the trend of increasing efficiency. But in the case of bar type, where the position of antenna is relatively close to head phantom, that trend didn't show. It was confirmed that the shape of handset has a great effect on the performance.

• Proceedings of the KIEE Conference
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• 2008.10b
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• pp.137-138
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• 2008

This paper proposes the modified image contrast enhancement technique for small-sized display of mobile handset. Sample images are user interface images, in which scaled up wVGA($800{\times}480$) from qVGA($320{\times}240$) that we can see easily in mobile handset. The display size of mobile handset is relatively small, so the goal of this paper is to simplify image contrast enhancement algorithm based on conventional HE (Histogram Equalization) algorithm and improve computational effectiveness to minimize power consumption in real hardware IC. In this paper, we adopt HE technique, which is classical and widely used for image contrast enhancement. At first, the input frame image is partitioned to temporal sub-frames and then analyzes gray level histogram of each sub-frame. In case that the analyzed histogram of some sub-frames deviates so much from reference level (it means that the sub-frame image components consist of too bright ones or dark ones), apply DHE(Dynamic Histogram Equalization) algorithm. In the other case, apply classical Histogram Linearization (or Global HE) algorithm. Also we compare the HE technique with gamma LUT (Look-Up Table) method, which is known as the simplest technique to enhance image contrast.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.10a
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• pp.636-639
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• 2008

The paper deals with the improvement of various characteristics of antenna for VHF mobile handset. In the general case, $1/4{\lambda}$ monopole and helical antenna are used for VHF mobile handset. However, various characteristics of antenna have different result for effect of hand. Especially, radiation efficient is reduced about several dB. In this paper, characteristics of loaded helical antenna have been evaluated. And we propose a method to improve a radiation efficient of antenna consider with hand effect.