• ETRI Journal
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• 제28권5호
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• pp.615-620
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• 2006

In this paper, we discuss the quantification of Mach-Zehnder interferometer (MZI) thermal stabilization which is needed in optical phase shaped binary transmission (PSBT) links. Considering the thermo-optic and thermal expansion effects, we revisit the analytical expression for the thermal drift (GHz/$^{\circ}C$) of the MZI center frequency (denoted here by the 'MZI spectral drift'). An MZI is then used in an experimental transmission system using the optical PSBT format. We study the effect of spectral MZI drift by using a thermally stabilized interferometer and applying a frequency shift to the optical carrier. By using the thermal drift coefficient of the MZI, we find that to ensure low bit error rate fluctuations due to the MZI drift, the thermal stabilization of the device must have an accuracy of $0.5^{\circ}C$.

• ETRI Journal
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• 제28권6호
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• pp.826-829
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• 2006

A novel method for optical phase shaped binary transmission (PSBT) generation has been recently reported and experimentally evaluated. An amelioration of the optical signal-to-noise ratio (OSNR) sensitivity of the optical PSBT modulation format is proposed with the application of the concepts of enhanced electrical PSBT signal generation. Enhanced optical PSBT is proposed here as a modulation format producing a 0.7 dB gain in OSNR sensitivity compared to OPSBT, while maintaining a good robustness to group velocity dispersion: 100 ps/nm for enhanced optical PSBT and 120 ps/nm for optical PSBT, compared to 50 ps/nm for standard NRZ signals.

• ETRI Journal
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• 제44권6호
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• pp.966-976
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• 2022

Optical wireless communication, or free space optics, is a promising solution for backhauls in sixth-generation mobile systems. However, the susceptibility of optical links to weather conditions has led to FSO links being furnished with radio frequency (RF) backups. These Hybrid FSO/RF systems provide enhanced link availability but lead to RF resource wastage. Cognitive radio technology, in contrast, is well known for its optimal use of RF resources and may be combined with an FSO link to create a Cognitive Hybrid FSO/RF system. This work uses such a system to analyze a configuration for a mobile backhaul in sixth-generation mobile systems. This configuration can seamlessly coexist with established large scale RF cellular networks. The performance of this configuration is analyzed with respect to outage probability and average bit error by considering the impact of optical channel turbulence, misalignment loss, RF interference, and noise. Mathematical closed-form expressions are verified by simulations.

• ETRI Journal
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• 제30권2호
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• pp.261-267
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• 2008

In this paper, we propose and demonstrate a cost-effective technique to upgrade the capacity of dense wavelength division multiplexing (DWDM) networks to a 40 Gb/s line rate using the existing 10 Gb/s-based infrastructure. To accommodate 40 Gb/s over the link optimized for 10 Gb/s, we propose applying a combination of super-FEC, carrier-suppressed return-to-zero, and pre-emphasis to the 40 Gb/s transponder. The transmission of 40 Gb/s DWDM channels over existing 10 Gb/s line-rate long-haul DWDM links, including $40{\times}40$ Gb/s transmission over KT's standard single-mode fiber optimized for 10 Gb/s achieves successful results. The proposed upgrading technique allows the Q-value margin for a 40 Gb/s line rate to be compatible with that of 10 Gb/s.

• ETRI Journal
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• 제34권1호
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• pp.122-125
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• 2012

A video signal through a high-density optical link has been demonstrated to show the reliability of optical link for high-data-rate transmission. To reduce optical point-to-point links, an electrical link has been utilized for control and clock signaling. The latency and flicker with background noise occurred during the transferring of data across the optical link due to electrical-to-optical with optical-to-electrical conversions. The proposed synchronization technology combined with a flicker and denoising algorithm has given good results and can be applied in high-definition serial data interface (HD-SDI), ultra-HD-SDI, and HD multimedia interface transmission system applications.

• ETRI Journal
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• 제29권2호
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• pp.162-168
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• 2007

A new scheme for bi-directional HDTV/Gigabit Ethernet/CATV transmission over a hybrid dense-wavelength-division-multiplexing passive optical network (DWDM-PON) is proposed and demonstrated. It is based on injection-locked vertical-cavity surface-emitting lasers and distributed-feedback laser diodes as transmitters. Services with 129 HDTV channels, a 1.25 Gbps Gigabit Ethernet connection, and 77 CATV channels are successfully demonstrated over 40 km single-mode fiber links. Good performance of bit error rate, carrier-to-noise ratio, composite second order, and composite triple beat is achieved in our proposed bidirectional DWDM-PON.

• ETRI Journal
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• 제28권4호
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• pp.517-520
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• 2006

In this letter, a new sharing mechanism, SRLG sharing, is proposed, which allows the links of the same shared risk link group (SRLG) in a primary light tree to share protections in WDM optical networks. In previous studies, how to share spare resources with SRLG constraints has not been studied in multicast optical networks. In this letter, considering SRLG sharing, we propose a novel algorithm -multicast with SRLG sharing (MSS)- to establish a protection light tree. Finally, the algorithm MSS and the algorithm multicast with no SRLG sharing (MNSS) are compared through a simulation to show that our new sharing scheme of SRLG sharing is more efficient than that of no SRLG sharing in terms of spare resource utilization and blocking probability.

• 전자공학회논문지
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• 제49권11호
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• pp.24-35
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• 2012

본 논문에서는 광 이더넷 시스템에 대하여 상용 광 트랜시버 모듈의 사용이 가능하면서도 에너지 절감기능을 제공할 수 있도록 트래픽 예측모듈을 사용하는 동적 레인제어방식을 제안한다. 40/100Gbps급 상용 광 트랜시버는 4개 또는 10개의 광 트랜시버를 사용하는데 이들 각각은 트래픽 부하와 상관없이 항상 켜져 있어 많은 에너지를 소모한다. 이러한 에너지 소모를 감소시키기 위하여 제안된 동적 레인제어방식은 부하에 따라 일부 레인의 트랜시버를 끄고 나머지 활성화된 레인으로만 프레임을 처리하도록 한다. 이때 레인의 갯수가 변동될 때 발생할 수 있는 바이트 전송순서 어긋남을 보완하기 위하여 새로운 전송율 제어모듈을 xGMII 인터페이스 상위에 위치한 정합부계층에 설치하는 것을 제안하였다. 이것은 비활성화된 레인상으로 가상적인 바이트열을 삽입하는 기능을 수행하는 것으로써 이 바이트열들은 비활성화된 PMD에서 무시된다. 실제 이 모듈의 구현은 PHY모듈과 별개로 동작하므로 상용 PHY모듈의 사용이 가능한 장점을 제공한다. 이러한 시스템에서 변동되는 부하에 적응하여 활성화된 레인의 갯수를 결정하는 것이 중요하므로 구현관점에서 용이한 트래픽 예측기를 제시하였다. 이것은 주기적으로 샘플링된 현재의 송신버퍼크기와 지금까지 사용되었던 버퍼크기 예측값에 서로 다른 가중치를 부여하여 변화하는 트래픽에 적응하도록 한다. 이러한 시스템에 대하여 OMNET++기반의 시뮬레이터를 구현하여 적응정도와 에너지 절감효과를 분석하였다.

• Journal of Multimedia Information System
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• 제6권1호
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• pp.23-30
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• 2019

A communications profile is a system that acquires information from communication links to an ambulance or other vehicle moving on a road and compiles a database based on this information. The equipment (six sets of HDTVs, fish-eye camera, satellite antenna with tracking system, and receiving power from the satellite beacon of the N-star) mounted on the roof of the vehicle, image data were obtained at Yokohama Japan. From these data, the polygon of the building was actually produced and has arranged on the map of the Geographical Survey Institute of a 50 m-mesh. The optical study (relationship between visibility rate and elevation angle) were performed on actual data taken by fish-eye lens, and simulated data by 3D-Map with polygons. There was no big difference. This 3D map system then predicts the communication links that will be available at a given location. For line-of-sight communication, optical analysis allows approximation if the frequency is sufficiently high. For non-line-of-sight communication, previously obtained electric power data can be used as reference information for approximation in certain cases when combined with predicted values calculated based on a 3D map. 3D maps are more effective than 2D maps for landing emergency medical helicopters on public roadways in the event of a disaster. Using advanced imaging technologies, we have produced a semi-automatic creation of a high-precision 3D map at Yokohama Yamashita Park and vicinity and assessed its effectiveness on telecommunications and ambulatory merits.

• ETRI Journal
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• 제37권6호
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• pp.1055-1064
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• 2015

We demonstrate a next-generation high-capacity mobile fronthaul based on radio over fiber (RoF) technology, which links between a digital unit and a radio unit supporting two frequency assignments and $2{\times}2$ multiple input, multiple output antennas. To confirm the technical feasibility of a mobile fronthaul, we experimentally investigate its down- and uplink end-to-end performances including the optical and radio frequency (RF) signal path. Frequency-dependent performance deviations, error vector magnitude variations, overall system performance variations caused by optical to electrical conversion, and intermediate frequency to RF conversions are examined. Experimental verifications on multiple LTE uplink signals are performed for the first time. We also demonstrate several commercial mobile Internet services, YouTube video streaming, and file transfers using off-the-shelf mobile devices, through a mobile fronthaul based on RoF.