• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.923-926
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• 2001

In this paper, we investigate a new approach pilot-symbol-aided channel estimation for orthogonal frequency division multi-plexing (OFDM) systems. Until now, lots of channel estimation methods are proposed. The pilot symbol assisted modulation (PSAM) has good performance. But, our proposed Algorithm has more good performance than the conventional PSAM system. Our algorithm is that channel estimation performance using the less inserted pilot-symbols systems is almost same to the two times inserted pilot-symbols system. The proposed method is highly robust to fast Rayleigh fading channel. Simulation results are presented to demonstrate the performance of our proposed algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.7
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• pp.1448-1458
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• 1997

In this paper the reverse link of the GLOBALSTAR-the representative CDMA LEO satellite system and LEO mobile satellite channel are developed by the SPW software simulation tool. And the performance of the system is evaluated. GLOBALSTAR is designed to give cellular-type service to hand-held user terminals through a constellation of 48 LEO satellites in circular orbites with 1414 Km altitude. Since LEO mobile satellite system communicates with mobile unit, it is suffered from severe multipath fading and shadowing. The fast mobility of LEO satellites makes the channel condition time vering. So, the LEO mobile satellite channel is different from land mobile channels. In this unique LEO satellite channel, it is shown that the performance of the GLOBALSTAR reverse link is varied according to the elevational angle, but this variation is overcome by satellite path diversity.

• Annual Conference of KIPS
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• 2009.11a
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• pp.679-680
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• 2009

Radio jamming attack is the most effective and easiest Denial-of-Service (DOS) attack in wireless network. In this paper, we proposed a multi-channel MAC protocol to mitigate the jamming attacks by using cognitive radio. The Cognitive Radio (CR) technology supports real-time spectrum sensing and fast channel switching. By using CR technologies, the legitimate nodes can perform periodic spectrum sensing to identify jamming free channels and when the jamming attack is detected, it can switch to un-jammed channel with minimum channel switching delay. In our proposed protocol, these two CR technologies are exploited for thwarting the jamming attacks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.2
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• pp.440-456
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• 2011

In this paper, we introduce a novel Public Key Infrastructure (PKI) based message authentication scheme that takes advantage of temporal and spatial uniqueness in physical layer channel responses for each transmission pair in vehicular communication networks. The proposed scheme aims at achieving fast authentication and minimizing the packet transmission overhead without compromising the security requirements, in which most messages can be authenticated through an extreme fast physical-layer authentication mechanism. We will demonstrate that the proposed secure authentication scheme can achieve very short message delay and reduced communication overhead through extensive analysis and simulation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.399-403
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• 2004

In this paper, we have analyzed the TCP throughput of Portable Internet system in 2.3GHz wireless environment with considering user's mobility speed. As the Portable Internet uses large cells compared to wireless LAM and supports user's nobility, we have adapted different wireless channel model to derive the TCP throughput of the system. We have assumed wireless channel is Rayleigh fading channel and the channel is modeled as two-state Markov model with which user's nobility speed can be considered by varying transition matrix of the model. from the simulation results, we have known that higher TCP throughput under the slow fading than under the fast fading. Because the TCP throughput is closely related to the sender's congestion control, the more congestion control is done by the sender, the lower TCP throughput we have. The more congestion control is caused in the sender under the fast fading than the slow fading so the lower TCP throughput is resulted in the fast fading environment.

• Journal of information and communication convergence engineering
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• v.4 no.4
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• pp.131-135
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• 2006

In this paper, we discusses that the theoretical analysis is made for the performance of FS MC-CDMA by the aid of the Nakagami fading channels and the block error probabilities of the FS MC-CDMA in Nakagami fading channel are presented. The channel fading speed, slow or fast, is considered in evaluating block error probabilities. The effectiveness of diversity combining in improving block error performance is examined.

• Journal of the Korea Society of Computer and Information
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• v.3 no.2
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• pp.155-160
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• 1998

We applied a pilot symbol assisted modulation technique to QPSK system for improving BER performance over mobile communication channel. We demonstrate through computer simulation, that the proposed scheme achieves a prominent improvement comparison to that of conventional QPSK in a fast flat Rayleigh fading environment.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.6
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• pp.608-614
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• 2015

A multi-channel audio CODEC with inter-channel interference suppression is proposed, in which channel switching noise-referred sampling error is significantly reduced. It also supports a coarse/fine mode operation for fast frequency tracking with good harmonic performance. The proposed multi-channel audio CODEC was designed in a 65 nm CMOS process. Measured results indicated that SNR and SNDR of ADC were 93 dB and 84dB, respectively, with SNDR improved by 43 dB. Those of DAC were 96 dB and 87 dB, respectively, with SNDR improved by 45 dB when all the channels are running independently.

• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.982-985
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• 2000

This paper presents channel estimation of an asynchronous W-CDMA reverse link using the interpolation and moving average algorithm in frequency-selective Rayleigh fading channel. The proposed algorithm is an interpolated decision-directed (IDD) block-wise moving average (BWMA) algorithm. The IDD-BWMA algorithm performs two- stage processes. The first stage performs data decision to make a virtual pilot channel by using linear interpolation channel estimation scheme. Then, the second stage performs the channel estimation of the “block-wise moving average” type by using a virtual pilot channel obtained in the first stage. By using Monte-Carlo computer simulations, we show that the proposed channel estimator is superior to other estimation schemes such as the WMSA(K=1) and DD-RAKE at higher Doppler frequencies, especially.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.05a
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• pp.95-98
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• 2009

RFID(Radio Frequency IDentification) technology is an automatic identification method using radio frequencies between RFID reader which collects the informatin and tag which transmits the information. RFID technology develops passive RFID which transmit the only ID to active RFID which transmit the additional information such as sensing information. there is ISO/IEC 18000-7 as typical standard of active RFID. it is single channel system of 433.92MHz and has limitation of collection of a number of tags. to overcome limitation of collection of many tags, we propose the new 2.4GHz active RFID technology which can use the multi-channel. if reader has multi-interface and uses another channel in each, reader could fast collect the tags. but, if a reader which has many interfaces collects tags through the specific interface, the performance may not improve any more comparing with a reader using single interface. in this paper, we show the fast collection through design and implementation of protocol for load balancing between interfaces in multi-interface RFID reader.