• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.8
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• pp.2663-2674
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• 2014

For cognitive radio sensor networks (CRSNs) that use underlay-based spectrum access, the location of the primary user (PU) plays an important role in the power control of the secondary users (SUs), because the SUs must keep the minimum interference level required by the PU. Received signal strength (RSS)-based localization schemes provide low-cost implementation and low complexity, thus it is suitable for the PU localization in CRSNs. However, the RSS-based localization schemes have a high localization error because they use an inexact path loss exponent (PLE). Thus, applying a RSS-based localization scheme into the PU localization would cause a high interference to the PU. In order to reduce the localization error and improve the channel reuse rate, we propose a RSS-based PU localization scheme that uses distance calibration for CRSNs using underlay model-based spectrum access. Through the simulation results, it is shown that the proposed scheme can provide less localization error as well as more spectrum utilization than the RSS-based PU localization using the mean and the maximum likelihood calibration.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.238-241
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• 2002

With the popularity of utilization of the Internet among people, the amount of data in the network rapidly increased. So that, the fall of response time from WWW server, which is caused by the network traffic and the burden on m server, has become more of an issue. This problem is encouraged the rearch by redundancy of requesting the same pages by many people, even though they browse the same the ones. To reduce these redundancy, WWW cache server is used commonly in order to store m page data and reuse them. However, the technical uses of WWW cache that different from CPU and Disk cache, is known for its difficulty of improving the cache hit rate. Consecuently, it is difficult to choose effective WWW data to be stored from all data flowing through the WWW cache server. On the other hand, there are room for improvement in commonly used cache replacement algorithms by WWW cache server. In our study, we try to realize a WWW cache server that stresses on the improvement of the stresses of response time. To this end, we propose the new cache replacement algorithm by focusing on the utilizable information of network distance from the WWW cache server to WWW server that possessing the page data of the user requesting.

• Journal of KIISE:Software and Applications
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• v.37 no.11
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• pp.845-850
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• 2010

Incremental parsing has been developed to reuse the parse result of the original string during the parsing of a new string. The previous incremental LL(1) parsing methods precomputed the reusable point information before parsing and used it during parsing. This paper proposes an efficient reusable point computation by factoring the common part of the computation. The common symbol storing method and the distance storing method were previously suggested to find the reusable point, and by combining the methods, this paper gives the storing method of the distance to common symbols. Based on it, an efficient incremental LL(1) parser is constructed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.8
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• pp.2003-2012
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• 1996

The 16- and 32-state Trellis-coded M-ary 4-dimensional (4-D) orthogonal modulation scheme with a frequency-reuse technique have been investigated. Here, 5 coded bits form a rate 4/5 convolutional encoder provide 32 possible symbols. Then the signals are mapped by a M-ary 4-D orthogonal modulator, where each signal has equal energy and is PSK modulated. In the M-ary 4-D modulator, we have employed the vectors which is derived by the optimization technique of signal waveforms in a 4-D sphere. This technique is usedin maximizing the minimum Euclidean distance between a set of signal poits on a multidimensional sphere. By combinig trellis coding with M-ary 4-D modulation and proper set-partitioning, we have obtained a considerable impeovement in the free minimum distance of the system over an AWGN channel. The 16-state scheme obtains coding gains up to 5.5 dB over the uncoded two-independent QPSK scheme and 2.5 dB over the two-independent 2-D TCM scheme. And, the 32-state scheme obtains coding gains up to 6.4 dB over the uncoded two-independent QPSK schemeand 3.4 dB over the two-independent 2-D TCM scheme.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.3
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• pp.341-346
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• 2017

In this paper, we present a 60 GHz on-off keying (OOK) modulator in a 90 nm CMOS. The modulator employs a current-reuse technique and a switching modulation for low DC power dissipation, high on/off isolation, and high data rate. The measured gain of the modulator, on/off isolation, and output 1-dB compression point is 9.1 dB, 24.3 dB, and 5.1 dBm, respectively, at 60 GHz. The modulator consumes power consumption of 18 mW, and is capable of handling data rates of 8 Gb/s at bit error rate of less than $10^{-6}$ for $231^{-1}$ PRBS over a distance of 10-cm with an OOK receiver module.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.1025-1031
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• 2001

In this paper, we derive the outage probability of cellular mobile system with STTB(Space Time Transmitter Diversity) scheme where the received radio signals and interferers experience Rayleigh fading and AWGN. The new probability density function of L independent identically distributed interferers is derived using Laplace transforms. We express the probability of outage as a function of the average-signal to average-interference power ratio and the signal to noise ratio. In addition, the frequency reuse distance which is one of the key parameters in the design of cellular systems is analyzed.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1993.06a
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• pp.1342-1345
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• 1993

In the cellular mobile communications as decreasing the cell radius to increse the reuse factor of frequencies, the handoff requests are increasing so that the efficient handoff decision making becomes a crucial problem. In this simulation study, we evaluate a set of handoff algorithms based on fuzzy-multicriteria decision making. These algorithms uses the parameters including the received signal strength intensity, the bit error rate and the distance between a mobile station and a base station. We compare the fuzzy algorithms in terms of call block ratio and handoff request ratio and call force ratio, and show the applicability of those algorithms in the cellular mobile communication systems.

• The Transactions of the Korea Information Processing Society
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• v.7 no.3
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• pp.901-908
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• 2000

Satellite communication in the 21 century's high tech information world is developing rapidly, marked by high levels of applications and functions. For example, satellite communication can process and switch the speed of the service provided by a broad and vast digital multimedia system such as a long-distance all between nations or broadcasting transfer service, which is supplied by a contemporary satellite system. So, it bring about problems which lack of satellite orbit and gibes out frequency resource by increment of satellite universally. To support this, an OBP satellite system is need, which includes an on-board IF/RF switch, baseband signal processing, multi-beam antenna technology, as well as a simple transponder system. In this paper, we have outlined the next generation of satellite communication; satellite OBP transport network architecture, which offers multimedia service and applied frequency reuse method for multi-spot beam. The satellite B-ISDN transport network architecture is also analyzed.

• Journal of Information Technology Services
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• v.9 no.2
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• pp.163-177
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• 2010

In this paper, we consider a channel ordering problem that seeks to maximize the service quality in mobile radio communication systems. If a base station receives a connection request from a mobile user, one of the empty channels belonging to the base station is assigned to the mobile user. In case multiple empty channels are available, we can choose one that incurs least interference with other channels assigned to adjacent base stations. However, note that a pair of channels that are not separated enough generates interference only if both channels are assigned to mobile users. That is, interference between channels may vary depending on the channel assignment sequence for each base station and on the distribution of mobile users. To find a channel assignment sequence that seems to generate minimum interference, we develop an optimization model considering various scenarios of mobile user distribution. Simulation results show that channel assignment sequence determined by the scenario based optimization model significantly reduces the interference provided that scenarios and interference cost are properly generated.

• Journal of the Optical Society of Korea
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• v.12 no.4
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• pp.346-350
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• 2008

In this paper, we analyze the performance of a reliable, scalable, and cost-effective switchless wavelength division multiplexing (WDM) network based on an arrayed waveguide grating (AWG). The network efficiency is significantly increased by spatially reusing wavelengths and exploiting multiple free spectral ranges (FSRs) of the AWG employed in the architecture. We have analyzed the performance of this architecture by simulating in $Optsim^{TM}$ with a control channel which exploits the broadband light source, i.e., an LED. The data was successfully transmitted to a distance of 30 km without using any EDFA's in the network, with a reasonable BER of $4.0530{\times}10^{-14}$. We have analyzed the performance of this architecture with a control channel which exploits the broadband light source, i.e., an LED, by simulating in $Optsim^{TM}$.