• Nuclear Engineering and Technology
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• 제29권6호
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• pp.468-475
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• 1997

The transient photocurrent in amorphous silicon radiation detectors (n-i-n and forward biased p-i-n) were analyzed. The transient photocurrents in these devices could be modeled using multiple trap levels in the forbidden gap. Using this model the rise and decay shapes of the photocurrents could be fitted. The decaying photocurrent shapes of the p-i-n and n-i-n devices after a short duration of light pulse showed a similar behavior at low dark current density levels, but at higher dark current density levels the photocurrent of the p-i-n diode decayed faster than that of the n-i-n, which could be explained by the decreased electron lifetimes in the forward biased p-i-n diode at high dark current densities. The transient photoconductive gain behaviors in the amorphous silicon radiation detectors are discussed in terms of device configuration, dark current density and time scale.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권10호
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• pp.5049-5062
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• 2016

This paper analyzes the secrecy performance of an amplify-and-forward (AF) relay network, where a multi-antenna eavesdropper attempts to overhear the transmitted message from a multi-antenna source to a multi-antenna destination with a single antenna relay. Firstly, we derive the approximate analytical expressions for the secrecy outage probability (SOP) and average secrecy rate (ASR) of the relay network. Then, asymptotic expressions of SOP and ASR at high main-to-eavesdropper ratio (MER) are also provided to reveal the diversity gain of the secure communication. Finally, numerical results are given to verify the theoretical analysis and show the effect of the number of antennas in the considered relay network.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권6호
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• pp.1606-1626
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• 2012

This paper investigates the performance of an amplify-and-forward (AF) two-way relaying system with antenna correlation. The system consists of two multiple-antenna sources, which exchange information via the aid of a single-antenna relay. In particular, we derive the exact outage probability expression. Furthermore, we provide a simple, tight closed-form lower bound for the outage probability. Based on the lower bound, we obtain the closed-form asymptotic outage probability and the average symbol error rate expressions at high signal-to-noise ratio (SNR), which reveal the system's diversity order and coding gain with antenna correlation. To investigate the system's throughput performance with antenna correlation, we also derive a closed-form lower bound for the average sum-rate, which is quite tight from medium to high SNR regime. The analytical results readily enable us to obtain insight into the effect of antenna correlation on the system's performance. Extensive Monte Carlo simulations are conducted to verify the analytical results.

• 한국정보통신학회논문지
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• 제12권7호
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• pp.1249-1255
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• 2008

1530nm 파장 대역이 L밴드 (long-wavelength-band) EDFA(erbium-doped fiber amplifler)를 위한 펌프 파장으로 연구되었다. 이 펌프 광원은 파장 가변 광원과 직렬 연결된 C 밴드 (conventional-band) EDFA로 제작되었다. 이 L밴드 EDFA는 순방향 펌핑 구조를 사용하였다. 1530nm 대역 내에서 1545nm 펌프 파장을 사용하였을 때 0.454B/mW 이득 계수를 얻었는데 이는 기존에 사용되는 1480nm 파장으로 펌핑 하였을 경우보다 2배 이상 높은 수치이다. 1530nm 파장 펌핑의 잡음지수는 가장 좋지 않은 경우가 6.36dB였는데 이는 1480nm 펌핑보다 0.75dB 높은 값이다. 제안된 펌핑 파장을 이용하는 L밴드 EDFA에서 얻은 이 같은 골은 이득 계수는 이 L밴드 EDFA가 전력 소모를 적게 한다는 것을 의미한다.

• 한국멀티미디어학회논문지
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• 제9권6호
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• pp.728-734
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• 2006

Carrier interferometry code is considered as a promising scheme that provides significant performance improvement via frequency diversity effect. Space-time coding is commonly employed to achieve a performance gain through space diversity. The combination of these techniques and forward error correction coding will lead to enhanced system capacity and performance. This paper presents a low-density parity check (LDPC) coded space-time orthogonal frequency division multiplexing (OFDM) transmission scheme with carrier interferometry code for high-capacity and high-performance mobile multimedia communications. Computer simulations demonstrate that the proposed mobile multimedia transmission system offers a considerable performance improvement of approximately 9dB in terms of Eb/No in the Rayleigh fading channel with relatively low delay spread, in comparison with space-time OFDM. Performance gains are further increased, comparing with traditional OFDM systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권7호
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• pp.3524-3542
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• 2017

In a single-source and multi-relay amplify-forward (AF) cooperative network, the outage probability and the power allocation are two key factors to influence the performance of an entire system. In this paper, an optimized AF relay selection by an exclusive method and near optimal power allocation (NOPA) is proposed for both good outage probability and power efficiency. Given the same power at the source and the relay nodes, a threshold for selecting the relay nodes is deduced and employed to minimize the average outage probability. It mainly excludes the relay nodes with much higher thresholds over the aforementioned threshold and thus the remainders of the relay nodes participate in cooperative forwarding efficiently. So the proposed scheme can improve the utility of the resources in the cooperative multi-relay system, as well as reduce the computational complexity. In addition, based on the proposed scheme, a NOPA is also suggested to approach sub-optimal power efficiency with low complexity. Simulation results show that the proposed scheme obtains about 2.1dB and 5.8dB performance gain at outage probability of $10^{-4}$, when compared with the all-relay-forward (6 participated relays) and the single-relay-forward schemes. Furthermore, it obtains the minimum outage probability among all selective relay schemes with the same number of the relays. Meanwhile, it approaches closely to the optimal exhaustive scheme, thus reduce much complexity. Moreover, the proposed NOPA scheme achieves better outage probability than those of the equal power allocation schemes. Therefore, the proposed scheme can obtain good outage probability, low computational complexity and high power efficiency, which makes it pragmatic efficiently in the single-source and multi-relay AF based cooperative networks.

• 한국전자통신학회논문지
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• 제3권3호
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• pp.170-176
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• 2008

인터넷의 발달로 인해 국제간 대용량의 광신호를 장거리 전송하기 위해서는 DWDM 시스템의 성능향상이 필수적으로 요구된다. 전송 용량을 높이기 위해서는 전송 속도를 높이거나, 채널수를 늘려야 하며 이런 요구 조건을 충족시키기 위하여 라인 코딩, 변조기술, 최적화된 광섬유, 광대역 광증폭 기술, 분산보상 기술, 순방향 에러정정기술 등이 적용되고 있다. 특히, 순방향 에러정정기술은 고속 대용량 트래픽을 장거리 전송하기 위한 혁신적인 기술로 각광 받고 있다. 본 논문에서는 순방향 에러정정기술의 세대별 발전 현황과 코딩이득을 분석하여 상용 시스템에 구현하는 방법을 제시하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권12호
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• pp.4432-4450
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• 2014

It is widely observed that in practical wireless cooperative communication systems, different links may experience different fading characteristics. In this paper, we investigate into the outage probability and channel capacity of two-way amplify-and-forward (TWAF) relaying systems operating over a mixed asymmetric Rician and Rayleigh fading scenario, with different amplification policies (AP) adopted at the relay, respectively. As TWAF relay network carries concurrent traffics towards two opposite directions, both end-to-end and overall performance metrics were considered. In detail, both uniform exact expressions and simplified asymptotic expressions for the end-to-end outage probability (OP) were presented, based on which the system overall OP was studied under the condition of the two source nodes having non-identical traffic requirements. Furthermore, exact expressions for tight lower bounds as well as high SNR approximations of channel capacity of the considered scenario were presented. For both OP and channel capacity, with different APs, effective power allocation (PA) schemes under different constraints were given to optimize the system performance. Extensive simulations were carried out to verify the analytical results and to demonstrate the impact of channel asymmetry on the system performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권10호
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• pp.4957-4976
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• 2016

This paper investigates the error performance of the amplify-and-forward (AF) relaying systems in the context of full-duplex (FD) communication. In addition to the inherent self-interference (SI) due to simultaneous transmission and reception, coexistent FD terminals may cause crosstalk. In this paper, we utilize the information exchange via the crosstalk channel to construct a particular distributed space-time code (DSTC). The residual SI is also considered. Closed-form pairwise error probability (PEP) is first derived. Then we obtain the upper bound of PEP in high transmit power region to provide more insights of diversity and coding gain. The proposed DSTC scheme can attain full cooperative diversity if the variance of SI is not a function of the transmit power. The coding gain can be improved by lengthening the frame and proper power control. Feasibility and efficiency of the proposed DSTC are verified in numerical simulations.

• 전자공학회논문지
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• 제51권4호
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• pp.49-58
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• 2014

본 논문에서는 저전력 고속 모바일 I/O 인터페이스를 위한 저스윙 차동 니어-그라운드 시그널링 (NGS) 트랜시버를 소개한다. 제안하는 트랜스미터는 온-칩 레귤레이터로 정류된 프로그래머블한 스윙을 가지는 전압-모드 드라이버와 비대칭 상승/하강시간을 가지는 전단드라이버를 사용한다. 제안하는 리시버는 고주파이득을 신장시키는 피드-포워드 커패시터를 이용한 새로운 다중경로이득 차동앰프를 사용한다. 또한, 이 리시버는 가변적인 트랜스미터 출력스윙에 의한 입력 공통모드 변화를 보상하며, 리시버 입력단 증폭기의 전류 미스매치를 최소화하기 위하여 새로운 적응형 바이어스 생성기를 포함한다. 트랜스미터와 리시버에 적용된 새로운 간단하고 효과적인 임피던스 매칭 기술들의 사용으로 우수한 시그널 인테그리티와 높은 파워 효율을 이뤄냈다. 65 nm CMOS 공정으로 설계된 제안하는 트랜시버는 10 cm 길이의 FR4 PCB에서 채널당 13 Gbps의 전송속도와 0.3 pJ/bit (= 0.3 mW/Gbps)의 높은 파워 효율을 갖는다.