• 한국통신학회논문지
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• 제29권10A호
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• pp.1177-1188
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• 2004

본 논문에서는 UWB Application을 위하여 IEEE 802.15 TG3a 의 표준안의 하나로 제안된 MB-OFDM 시스템의 성능을 분석하고, IEEE 802.15 SG3a 에서 제안된 60Hz의 광대역 UWB 채널모델을 MB-OFDM 시스템의 주파수 대역 및 중심 주파수 호핑을 고려하여 기존의 UWB 채널을 필터링한 3개의 서브 맨드 채널로 재성형한다. 시뮬레이션을 통해서 AWGN 과 UWB 채널 환경에서 bm-OFDM 시스템의 성능을 비교하고, 시간 영역 확산 및 주파수 영역 확산 기법으로부터 얻을 수 있는 주파수 및 시간 영역 다이버서티 이득을 검증하며, SFBC MB-OFDM 시스템과 기존 MB-OFDM 시스템과의 성능을 비교 분석한다. 시뮬레이션 결과에 의하면, SFBC를 사용하는 경우 기존의 MB-OFDM 시스템보다 10-4 BER 에서 약 1.5dB 정도의 Eb/No 성능을 향상시킴을 알 수 있다.

• 한국통신학회논문지
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• 제33권1A호
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• pp.50-58
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• 2008

다중사용자 무선 채널 환경에서 공간분할 다중접속 기법을 사용함으로서 전체 시스템의 전송률을 대폭 증가시킬 수 있다. 송신단에서 정확한 채널정보를 알고 있는 경우, 전송률을 적절하게 조절함으로서 시스템 성능을 보다 향상시킬 수 있다. 뿐만 아니라, 주파수 선택적 페이딩 특성을 갖는 광대역 무선 채널에서는 채널 부호화를 통해 채널 다이버시티를 활용하여 신뢰성이 높은 데이타 전송이 가능하도록 BIC-OFDM 기술을 사용한다. 본 논문에서는 제한된 궤환정보를 이용한 기회적 스케줄링 기법과 결합된 적응 변조 시스템을 제안하고자 한다. 제안된 기법은 주파수 다이버시티와 다중 사용자 다이버티시를 이용하여 링크 성능을 항샹시킬 수 있다. 또한, 적은양의 궤환정보를 위해 모든 부채널 대신 하나의 OFDM심볼을 기준으로 적응 변조 기법을 사용한다. 모의 실험에서는 본 논문에서 제안한 기법이 적절한 계산복잡도를 가지면서도 상당한 링크 성능 향상이 있음을 보여주고자 한다.

• Journal of electromagnetic engineering and science
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• 제5권1호
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• pp.31-35
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• 2005

This paper presents low form factor dual polarized antenna incorporating low profile annular ring patch antenna having 90$^{\circ}$ phase delay element for circular polarization(CP) and a reactive-loaded monopole linear polarized(LP) antenna. Both types of receiving antennas operate in the same frequency region from 2.320 GHz to 2.345 GHz, while different polarizations are used to take advantage of polarization diversity. The proposed CP antenna has good broadside radiation patterns, while the LP antenna reveals monopole-like radiation patterns. The gains of the antennas are measured to be 1.93 dBi and 2.24 dBi for CP and LP, respectively.

• 한국멀티미디어학회논문지
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• 제19권3호
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• pp.620-625
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• 2016

In this paper, we offer the secrecy outage probability of the amplify-and-forward (AF) transmission, which consists of one source, one destination, one relay, and one passive eavesdropper. Particularly, we consider that the relay is equipped with multiple antennas while other terminals is utilized with single antenna and apply diversity techniques (for both the reception and the transmission) at the relay to achieve gains in a secrecy outage performance. Additionally, we analyze the exact secrecy outage probability of the proposed systems in a one-integral form. Finally, some numerical examples are given to verify our provided analytical results for different system conditions.

• Journal of information and communication convergence engineering
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• 제6권3호
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• pp.353-357
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• 2008

One objective in developing the next generation of wireless communication systems is to increase data rates and reliability. A promising way to achieve this is to combine multiple-input and multiple-output signal processing with a space-time coding scheme, which offers higher coding and diversity gains and improves the spectrum efficiency and reliability of a wireless communication system. It is noted, however, that time delay differences and phase differences among different channels increase symbol interference and degrade system performance. In this letter, we investigate phase differences and their effects on multiple-input and multiple-output systems, and propose a compensation algorithm for the Rayleigh fading model to minimize their effects.

• 전자공학회논문지A
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• 제32A권4호
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• pp.24-31
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• 1995

In this paper, the dual-mode burst-error-correcting decoding algorithm is adapted to the multiple trellis-coded .pi./4 shift QPSK in order to achieve the improvement of bit error rate (BER) performance over fading channels. The dual-mode adaptive decoder which combines maximum likelihood decoding with a burst detection scheme usually operates as a Viterbi decoder and switches to time diversity error recovery whenever an uncorrectable error pattern is identified. Rayleigh fading channels and Rician fading channels having the Rician parameter K=5dB are used in computer simulation, and the simulation results are compared with those of interleaving techniques. It is shown that under the constraint of the fixed overall memory quantity, the dual-mode adaptive decoding scheme gains an advantage in the BER performance with respect to interleaving strategies.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.490-490
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• 2000

Parallel genetic algorithms are particularly easy to implement and promise substantial gains in performance. Its basic idea is to keep several subpopulations that are processed by genetic algorithms. Furthermore, a migration mechanism produces a chromosome exchange between subpopulation. In this paper, a new selection method based on non-linear fitness assignment presented. The use of proposed ranking selection permits higher local exploitation search, where the diversity of populations is structure. Experimental results show that the relation between local-global search balance and the probabilities of reaching a desired solution.

• ETRI Journal
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• 제28권5호
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• pp.680-683
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• 2006

One objective in developing the next generation of wireless communication systems is to increase data rates and reliability. A promising way to achieve this is to combine multiple-input and multiple-output signal processing with a space-time coding scheme, which offers higher coding and diversity gains and improves the spectrum efficiency and reliability of a wireless communication system. It is noted, however, that time delay differences and phase differences among different channels increase symbol interference and degrade system performance. In this letter, we investigate phase differences and their effects on multiple-input and multiple-output systems, and propose a compensation algorithm for the Rayleigh fading model to minimize their effects.

• 전기학회논문지
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• 제65권12호
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• pp.2177-2182
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• 2016

Using the existing exact but quite complicated symbol error rate (SER) expressions for M-ary phase shift keying (M-PSK) and M-ary differential phase shift keying (M-DPSK), we derive effective and concise closed-form asymptotic SER formulas especially in Rician-Nakagami fading channels. The derived formulas can be utilized to efficiently verify the achievable error rate performances of M-PSK and M-DPSK systems for the Rician-Nakagami fading environments. In addition, by exploiting the modulation gains directly obtained from the asymptotic SER formulas, we also theoretically demonstrate that M-DPSK suffers an asymptotic SER performance loss of 3.01dB with respect to M-PSK for a given M in Rician-Nakagami fading channels at high signal-to-noise ratio (SNR).

• Journal of Communications and Networks
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• 제18권1호
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• pp.19-26
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• 2016

In this paper, the performance of dual-hop multi-relay maximum ratio transmission (MRT) over Rayleigh flat fading channels is studied with both conventional (all relays participate the transmission) and opportunistic (best relay is selected to maximize the received signal-to-noise ratio (SNR)) relaying. Performance analysis starts with the derivation of the probability density function, cumulative distribution function and moment generating function of the SNR. Then, both approximate and asymptotic expressions of symbol error rate (SER) and outage probability are derived for arbitrary numbers of antennas and relays. With the help of asymptotic SER and outage probability, diversity and array gains are obtained. In addition, impact of imperfect channel estimations is investigated and optimum power allocation factors for source and relay are calculated. Our analytical findings are validated by numerical examples which indicate that multi-relay MRT can be a low complexity and reliable option in cooperative networks.