• Proceedings of the IEEK Conference
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• 2001.06a
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• pp.213-216
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• 2001

In this paper, the performance of an OFDM/CDMA system with turbo coding is analyzed and simulated in a multipath fading channel. Bit error probability is derived fDr a Rayleigh fading channel. In an OFDM/CDMA system, an OFDM and a CDMA techniques are combined to exploit the advantages of both techniques. For decoding of turbo code, MAP decoding algorithm is employed. From the simulation results. it is demonstrated that turbo coding offers considerable coding gain with reasonable encoding/decoding complexity. Also, it is shown that the BER performance is substantially improved by increasing the interleaver length for a fixed code rate and the increasing number of iterations used in the decoding process. The results in the paper can be applied to the design of OFDM-based CDMA system.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.9
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• pp.26-33
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• 1994

In this paper, the performance of the trellis coded CPFSK with the coherent detection over mobile communication channels is calculated. The characteristics of channels, including phase jitter effects and fading effects, are examined and modeled. The phase jitter channel is modeled to have a nonzero mean and a gaussian distribution. The fading channel has a Rayleigh distribution in the multipath. For the optimal decoding method(MLSE), the Viterbi algorithm is used for the trellis structure of trellis coded CPFSK. The results indicate that the trellis coded CPFSK with a small moulation indes gets more sensitive, as the index gets smaller, to the phase noise under the phase jitter channel. Using the interleaving method. It gives considerable improvements in the error rate under the fading channel.

• Journal of the Korea Computer Industry Society
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• v.2 no.9
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• pp.1209-1218
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• 2001

In this dissertation, we propose a dynamic source routing protocol supporting asymmetric path for mobile ad hoc networks. At present, the existing dynamic source routing protocol supports only symmetric path for routing. However, in fact, there can exist unidirectional links due to asymmetric property of mobile termenals or current wireless environment. Thus, we implement a mobile ad hoc routing protocol supporting asymmetric routing path, which is fit for more general wireless environment. Especially, the proposed protocol uses an improved multipath maintenance method in order to perform rapid route reconfiguration when route error due to mobility is detected.

• Proceedings of the Korea Information Processing Society Conference
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• 2016.10a
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• pp.106-107
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• 2016

Vehicular Adhoc Network는 accident warning, road condition message와 같은 도로상의 정보를 vehicle-to-vehicle 통신을 통해 주어진 목적지까지 얼마나 빠르고 정확하게 전송하는 것이 주요 이슈이다. 무선 센서 네트워크의 많은 타입들 중에서 VANET 환경에 적합한 source 기반의 라우팅 프로토콜은 불안정한 이동 네트워크의 역할을 충실히 수행할 수 있다. Source 라우팅 기법들을 연구하는데 road topology와 map 정보가 사용되며, 본문에서는 도로의 상황과, 라우팅이 직접 수행되는 영역을 부분으로 나누어 각 영역에 속한 이동 노드를 파악하여 다중 경로 라우팅 방안을 제시하여 error 발생과 link fail에 대한 신속한 대처를 수행한다.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 1997.11a
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• pp.407-415
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• 1997

In this paper, we apply a digital modulation scheme called Multi-Carrier CDMA (MC-CDMA) to the technique for cochannel interference cancellation using reference correlator, previously proposed. The cancellatoin method will be effective for reducing the interference components which are other users'signal components in a common channel, but fading effect of channel remains as the degrading factor of channel condition. For compensating it, MC-CDMA scheme is introduced to combat agianst the multipath fading. We analize above system and derive the average probability of error in AWGN and Rayleigh fading environment.

• 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.

• The Journal of the Acoustical Society of Korea
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• v.17 no.4
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• pp.28-34
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• 1998

미래 개인 휴대통신에서는 고속의 데이터 서비스를 위하여 높은 대역폭 효율을 요 구하게 된다. 무선통신 서비스를 향상시키기 위하여 코딩기법, 변조기법, 다중화기법 등의 다양한 방법이 연구되고 있다. 이중에서 특히 변조기법은 시스템의 성능을 결정하는 중요한 요소가 된다. 본 논문에서는 PSK. OQPSK, π/4 DQPSK, MSK, GMSK의 다섯가지 변조기 법에대한 BER성능을 시뮬레이션하였다. 시뮬레이션을 위한 다중경로 페이딩채널로서 3가지 서로 다른 채널을 적용하였다. 이때 시뮬레이션을 위하여 1.544Mbps의 전송속도와 1.9GHz 의 반성주파수 환경을 고려하였다. 또한 fractional 선형 등화기를 적용하여 변조방식에 따른 성능향상 정도를 비교하였다. 채널 Ⅰ, Ⅱ, Ⅲ에 대해 각각 30dB, 20dB, 10dB 정도에서 error floor현상이 발생했으며 π/4 DQPSKS가 가장 낮은 BER 특성을 보인 반면 QPSK는 가장 높은 BER을 나타냈다. 등화기를 적용했을 때는 GMSK의 성능향상이 가장 크게 나타 났다.

• Journal of information and communication convergence engineering
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• v.5 no.3
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• pp.229-232
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• 2007

This paper investigates on the use of constant-amplitude zero-autocorrelation (CAZAC) sequence for channel estimation in multiple-input multiple-output (MIMO) system over indoor wireless channel. Since the symbol-length of the conventional 4-phase CAZAC sequence is short, there is a limitation to use it for MIMO system in multipath environments. An algorithm which generates longer CAZAC sequences is proposed to overcome that problem. Flexible symbol-length of 4-phase CAZAC sequences can be made by the proposed algorithm. Therefore appropriate symbol-length of CAZAC sequences could be utilized as preambles in accordance with the number of transmit antennas and channel condition. The effect of the number of CAZAC sequences for channel estimation is presented in terms of mean square error (MSE).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.4
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• pp.817-823
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• 2010

MC-DS-CDMA is technique where a single data symbol is transmitted at multiple subcarriers which are orthogonal to each other. With this technique, frequency diversity can be achieved. The performance of PSAM MC-DS-CDMA system with the application of MRRC antenna diversity is analyzed. The BER performance of this system over multipath fading environment is evaluated, considering the channel estimation error, carrier frequency offset, and the nonlinear high power amplifier.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.7
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• pp.1777-1786
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• 1996

This paper describes theories and implementation techniques of a digital high-definition television(HDTV) modem based on 32-QAM for terrestrial broadcasting. We proposed a digital demodulation scheme and a symbol timing recovery structure based on the band edge component maximization(BECM) method. The adaptive equalizer has 256 complex taps to remove the multipath of delays ranging from -2.mu.s~+24.mu.s with a new T/2-spaced blind equalization algorithm. computer simulation results reveal that the proposed algorithm outperforms other conventional blind equalization algorithm a digital HDTV modem with 4.91MHz symobol rate is implemented by utilizing the proposed algorithms. All processings for modem operations such as demodulation, estimation of symbol timing phase error, adaptive equalization, and carrier recovery except IF signal processing and sampling phase control part of the AD converter are done in digital domain. Especially, the carrier recovery loop can track a carrier offset of upto .+-.350KHz.