• The Journal of the Acoustical Society of Korea
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• v.14 no.1
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• pp.48-55
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• 1995

The capacity of a digital cellular CDMA system is evaluated by computer simulation for reverse link (mobile-to-base) with 37 hexagonal cells including 3 rings from a center cell. It is assumed that the channels have shadow fading and the system is ideally power controlled. In this paper the capacity of CBMA system is evaluated for various propagation exponents, voice activity factors and neighboring cell traffics. The following results are obtained. The capacity of CDMA system is increased according to the increase of the propagation exponents and the decrease of the voice activity factors. Its capacity is about 15 and 5 times larger thari that of analog cellular FM/FDMA and digital cellular TDMA for $\gamma=4$ respectively, and is very sensitive to the neighboring cell traffics.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.4
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• pp.51-58
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• 2004

Push-pull structure with balun transformer is presented for load modulation technique which improves the overall efficiency of power amplifier Under the assumption that output impedance of fumed-off amplifier is high, conventional Doherty amplifier is composed of impedance inverter and peaking amplifier, of which operation is controlled by the input power level. In many case, however, impedance of 'off'amplifier is very low due to matching network or parasitic output capacitance. This paper introduces novel load modulation technique which uses low output impedance of 'off'amplifier. Experimental results show that good linearity and efficient!'enhancement of the proposed push-pull structure

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.11
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• pp.1311-1317
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• 2010

In this paper, for a uplink space division multiple access system named cooperative spatial multiplexing(CSM), radio resource management(RRM) algorithms are proposed based on sharing uplink channel information among a serving base station(BS) and interfering BSs in a uplink coordinated wireless communication system. A constrained maximum transmit power algorithm is proposed for mobile station(MS) to limit uplink inter-cell interference(ICI). And joint scheduling algorithm among coordinated BSs is proposed to enhance uplink capacity through ICI mitigation by using channel information from interfering BSs. It is shown that the proposed RRM algorithm provides a considerable uplink capacity enhancement by effective ICI mitigation only with moderate complexity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.2
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• pp.159-164
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• 2005

When an optical pulse propagates through the atmospheric channel, the atmospheric turbulence attenuates and spreads this pulse. This attenuation and broadening of pulse are occurred by the fluctuation in the arrival time of pulse at the optical receiver. This pulse broadening induces the intersymbol interference (ISI) between the adjacent pulses. finally, the adjacent pulses are overlapped and the bit rate and the repeaterless transmission length are limited by the ISI. In digital communication system, therefore, the pulse broadening is more important factor than the attenuation. In this paper, thus, we find the ISI in the atmospheric turbulence as the function of the structure constant for the refractive index fluctuation that presents the strength of turbulence using the temporal momentum function and present it by numerical analysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9A
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• pp.1005-1012
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• 2004

In this paper, we have analyzed minimum performance required for W-CDMA Handset from standard and Implemented the receiver for W -COMA Handset. We have derived the noise figure and IIP3 of receiver and determined the selectivity about adjacent channel and minimum performance for front-end stage. Before the Implementation, we have verified the performance using AOS simulator In conclusion, we have implemented the receiver for W-COMA Handset using the heterodyne architecture and performed measurement. Therefore, this paper wlll gIVe a guideline for design of the W -COMA Handset.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.5
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• pp.724-730
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• 2002

Digital communication systems are required to cause the minimum interference to adjacent channels, they must therefore employ the linear power amplifiers. In respect to linear power amplifiers, there are many linearization techniques. Feedforward power amplifier represent very wide bandwidth and high linearization capability. In the feedforward systems, overall efficiency is reduced due to the loss of delay line. In this paper, delay filter instead of transmission delay line adapted to get more high efficiency. Experimental results showed that ACLR (Adjacent Channel Leakage Ratio) has improved 17.43(dB), which is added 3.44(dB) by using the delay filter.

• Journal of Navigation and Port Research
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• v.26 no.3
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• pp.295-302
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• 2002

Currently digital communication system adapt various digital modulation schemes. All these communication systems are required to cause the minimum interference to adjacent channels, they must therefore employ the linear power amplifiers. In respect to linear power amplifiers, there are many linearization techniques. Feedforward power amplifier represent very wide bandwidth and high linearization capability. In the feedforward systems overall efficiency is reduced due to the loss of delay line. In this paper, delay filter instead of transmission delay line adapted to get more high efficiency. Experimental results showed that ACLR has improved 17.04dB which is added 2.54dB by using the delay filter.

• Journal of Advanced Navigation Technology
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• v.6 no.4
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• pp.273-278
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• 2002

In this paper, we provide the Interference Canceller Systems(ICS) in the wireless environments in the presence of co-existing ETACS and CDMA digital cellular systems to effectively cancel the interference than the established canceller systems. We proved the enhanced cancelling performances more than 29 dB cancellation characteristics between co-existing ETACS and CDMA digital cellular systems and the stabilized system characteristics in the rapidly changing wireless circumstances.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6C
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• pp.429-437
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• 2008

Multiple-input multiple-output (MIMO) techniques can be used for the spectral efficiency enhancement of the cellular systems, which can be categorized into spatial multiplexing (SM) and spatial diversity schemes. MIMO systems suffer a severe performance degradation due to the intercell interference from the adjacent cells as the mobile terminal moves toward the cell boundary. Therefore for the spectral efficiency enhancement, an appropriate transmission scheme for the given channel environment and reception scheme which can mitigate the intercell interference are required. In this paper, we propose an adaptive signal transmission/reception scheme for the spectral efficiency improvement of $M_R{\times}M_T$ MIMO systems, present the decision criteria for the adaptive operation of the proposed scheme, and demonstrate the performance gain. The proposed scheme performs adaptive transmission using spatial multiplexing and spatial diversity, and adaptive reception using maximal ratio combining (MRC) and intercell spatial demultiplexing (ISD) when the spatial diversity transmission is used at the transmitter. Spatial multiplexing/demultiplexing is performed at the high signal-to-interference ratio (SIR) range, and the transmit diversity in conjunction with the adaptive reception uses either conventional MRC or ISD which can mitigate the $M_R-1$ interference signals, based on the mobile location. For the performance evaluation of the proposed adaptive scheme, the probability density function (pdf) of the effective SIR for the transmission/reception methods in consideration are derived for $M_R{\times}M_T$ MIMO systems. Using the results, the average effective SIR and spectral efficiency are presented and compared with simulation results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.8
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• pp.683-691
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• 2013

This paper address a new scheme that alleviates the packet collision problem caused by contentions among nearby coordinators (CNs) in IEEE 802.15.4 meshed sensor networks. In existing studies, the number of retransmissions is reduced by adjusting the proper backoff period (BP) of sensor nodes, or unnecessary energy consumption is diminished by increasing channel utilization efficiently based on traffic load. In contrast, the proposed scheme avoids contentions among nearby CNs, thereby it enhances the energy efficiency of sensor nodes. To achieve this, the proposed scheme separates the starting points of CNs' contention periods and reduces contentions and collisions among overlapping CNs. According to our simulation results, the proposed scheme shows improved performance in terms of energy consumption, throughput, the number of collisions, and average delay for all conditions.