• ETRI Journal
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• v.42 no.2
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• pp.163-174
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• 2020

Numerous wearable technology companies have recently developed several headmounted display (HMD) products for virtual reality (VR) services. 5G wireless networks aim at providing high-quality 3D multimedia services such as VR, augmented reality, and mixed reality. In this study, we examine the application of millimeter-wave (mmWave) technology to realize low-latency wireless communication between an HMD and its content server. However, the propagation characteristics of mmWave present several challenges such as the deafness, blockage, and beam alignment problems, and interference among content servers. In this study, we focus on an environment that provides VR services in the mmWave band and introduce existing techniques for addressing such challenges. In addition, we employ a commercialized IEEE 802.11ad VR dongle to measure the actual data rate of an mmWave VR application and identify the degree to which the performance deteriorates when the above problems occur. Finally, we verify the feasibility of the proposed solutions through a simulation of several VR scenarios in the mmWave band.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.8
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• pp.52-59
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• 2007

In this paper, we analyzed and measured implant isolation characteristics for a 1.25 Gbps monolithic integrated hi-directional (M-BiDi) optoelectronic system-on-a-chip, which is a key component to constitute gigabit passive optical networks (PONs) for a fiber-to-the-home (FTTH). Also, we derived an equivalent circuit of the implant structure under various DC bias conditions. The 1.25 Gbps M-BiDi transmit-receive SoC consists of a laser diode with a monitor photodiode as a transmitter and a digital photodiode as a digital data receiver on the same InP wafer According to IEEE 802.3ah and ITU-T G.983.3 standards, a receiver sensitivity of the digital receiver has to satisfy under -24 dBm @ BER=10-12. Therefore, the electrical crosstalk levels have to maintain less than -86 dB from DC to 3 GHz. From analysed and measured results of the implant structure, the M-BiDi SoC with the implant area of 20 mm width and more than 200 mm distance between the laser diode and monitor photodiode, and between the monitor photodiode and digital photodiode, satisfies the electrical crosstalk level. These implant characteristics can be used for the design and fabrication of an optoelectronic SoC design, and expended to a mixed-mode SoC field.

• Information and Communications Magazine
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• v.30 no.12
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• pp.37-50
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• 2013

아이폰을 비롯한 새로운 스마트 기기의 도입으로 촉발된 폭발적인 데이터 트래픽의 증가는 사회.경제적으로 큰 변화를 가져 왔으며, 앞으로도 그 추세가 계속될 것으로 예측되고 있다. 국내의 경우 증가하는 데이터 트래픽을 수용하기 위해 10MHz의 LTE 시스템을 도입하여 상용 서비스를 시작한 바 있으며, 올해 하반기부터는 20MHz의 광대역 LTE 서비스와 함께 2개의 반송파를 집성하는 CA(Carrier Aggregation) 기술이 적용된 LTE-Advanced, 즉 4G 상용 서비스를 이미 개시하였다. LTE 상용 서비스가 본격화 되기 시작하면서 제조업체와 대학, 연구소 등을 중심으로 다음 세대 이동통신 기술에 대한 관심이 보다 높아졌으며, 최근 LTE-Advanced 상용 서비스 개시를 계기로 5G 이동통신에 대한 논의가 본격적으로 시작되고 있다. ITU-R WP(Working Party) 5D는 2012년 7월에 개최된 제13차 회의에서 2020년 및 그 이후의 미래 IMT 시스템을 위한 비전(Vision) 및 기술동향 연구를 수행하기로 결정하였으며, 2013년부터 본격적인 연구에 착수하여 미래 IMT 기술동향 보고서와 미래 IMT 비전 권고를 각각 2014년과 2015년까지 개발할 계획이다. 이와 관련하여 3GPP와 IEEE 802도 현재 표준화가 진행되거나 진행 예정인 최신 기술들을 중심으로 미래 IMT 기술동향 보고서에 대한 기고를 제출하였다. 향후 ITU-R WP 5D는 전례로 볼 때 현재 진행 중인 2020년 및 그 이후의 미래 IMT 시스템을 위한 비전 및 기술동향 연구 작업이 마무리하면, 4G인 IMT-Advanced의 경우와 마찬가지로 5G의 기술적 요구사항을 정의하고, 5G 후보 기술규격을 외부 표준화 기구들로부터 제안 받아 5G 기술로 승인하는 과정을 밟게 될 것이며, 이후 이 요구사항을 만족하는 시스템을 5G 이동통신 시스템이라고 명명하게 될 것이다. 5G 이동통신 시스템에 대한 요구사항은 다양한 의견 교류를 통해 큰 틀에서 컨센서스를 이루어가는 중이며, 이러한 내용이 ITU-R WP 5D의 기술적 요구사항에 반영되어 보다 구체화 될 것이다. 반면 5G에 대한 기술적 접근방법에 대해서는 여러 시각들이 존재하는 것이 사실이나, 현재 이에 대한 논의가 활발히 진행되고 있으며, 결국은 관련 표준화 기구들에서의 논의를 통해 그 접근방법이 최종적으로 결정될 것으로 보인다. 본 고에서는 먼저 5G 이동통신 요구사항과 4G 이후의 표준화 기술에 대해 살펴 본 후, 향후 이동통신 기술이 어떤 시나리오에 따라 발전할 것인지, 5G 네트워크는 어떤 구조를 갖게 될지, 그리고 어떤 기술이 적용될 지 등에 대해 개인적인 시각에서 전망해보고자 한다.

• Journal of the Korea Convergence Society
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• v.11 no.6
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• pp.43-49
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• 2020

In spite of the notable advancements of millimeter wave communication technologies, the 60 GHz Wi-Fi is still not widespread yet, mainly due to the high limitation of coverage. Conventionally, it has been hardly possible to support a high data rate with fast beam adaptation while keeping atmospheric beamforming coverage. To solve these challenges in the 60 GHz communication system, holistic system designs are considered. we implemented an enhanced design LDPC decoder enabling 6.72 Gbps coded-throughput with minimal implementation loss, and our proposed phase-tracking algorithm guarantees 3.2 dB performance gain at 1 % PER in the case of 16 QAM modulation and LDPC code-rate 3/4.

• Journal of Navigation and Port Research
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• v.33 no.3
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• pp.193-197
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• 2009

In this paper, the EM wave absorber was designed and fabricated for improvement of Wireless LAN environment at 2.4 GHz. We fabricated several samples in different composition ratios of Sendust and CPE(Chlorinated Polyethylene). Absorption abilities were simulated in accordance with different thicknesses of the prepared absorbers and changed complex relative permittivity and permeability due to composition ratio. The mixing ratio of Sendust and CPE was searched as 80: 20 wt.% by experiments and simulation Then the EM wave absorber was fabricated and tested using the simulated data. As a result, the EM wave absorber was fabricated based on simulated data. Simulated and measured results agreed well. As a result, the developed EM wave absorber with thickness of 3.25 mm has absorption ability of 19 dB at 2.4 GHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.755-761
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• 2005

In this paper, we proposed a channel estimation method by impulse signal train in OFDM. In order to estimate the channel response, 4 impulse signals are generated and transmitted during one OFDM (Orthogonal Frequency Division Multiplexing) symbol. The intervals between the impulse signals are all equal in time domain. At the receiver, the impulse response signals are summed and averaged. And then, the averaged impulse response signal is zero padded and fast Fourier transformed to obtain the channel estimation. The BER performance of the proposed method is compared with those of conventional estimation method using the long training sequence in fast fading environments. The simulation results show that the proposed method improves by 3 dB in terms of Eb/No, compared with the conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.282-290
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• 2006

In this paper, we propose an enhanced Timing Estimator algorithm for 2.45GHz LR-WPAN receiver. Because an expensive and highly efficient oscillator can't be used for low-cost implementation, a Timing Estimator algorithm having stable operation in the channel environment with center frequency tolerance of 80 ppm is required. To enhance the robustness to frequency offset and the stability of receiver performance, multiple delay differential filter is adopted. By utilizing the characteristic that the correlation result between the output signal of Multiple delay differential filter and reference signal is restricted on the In-phase part of the correlator output, a coherent detection scheme instead of the typical noncoherent one is adopted for Timing Estimator. The application of the coherent detection scheme is suitable for LR-WPAN receiver aimed at low-cost, low-power, and low-complexity, since it can remove performance degradation due to squaring loss of I/Q squaring operation and decrease implementation complexity. Computer simulation results show that the proposed algorithm achieved performance improvement compared with the differential detection-based noncoherent scheme by 2dB in average.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4A
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• pp.324-329
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• 2009

In this paper, a novel Snowflake-shaped microstrip patch antenna for application in the WLAN(5.2/5.8GHz) band is designed and fabricated. The size of antenna is $21.2{\times}16mm^2$ and substrate is used Taconic-RF30. To obtain sufficient bandwidth in Return loss <-10dB and dual resonance characteristic, the Short-pin is inserted on the patch and the coaxial probe source is used. The measured results of fabricated antenna show 220MHz and 135MHz bandwidth in Return loss <-10dB referenced to the WLAN(5.2/5.8GHz) band. The measured antenna gain is $4.7{\sim}6.9dBi$ in the WLAN(5.2/5.8GHz) band. The experimental 3-dB beam width in I-plane and H-plane are $73.2^{\circ}/82.75^{\circ}$ for 5.1500Hz, $74.56^{\circ}/83.63^{\circ}$ for 5.3500Hz, and $86.24^{\circ}/85.15^{\circ}$ for 5.7850Hz, respectively.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.5 s.335
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• pp.55-62
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• 2005

In this paper, we propose an efficient symbol detection algorithm for space-frequency OFDM (SF-OFDM) transmit diversity scheme and present the implementation results of the SF-OFDM WLAN baseband processor with the proposed algorithm. When the number of sub-carriers in SF-OFDM scheme is small, the interference between adjacent sub-carriers may be generated. The proposed algorithm eliminates this interference in a parallel manner and obtains a considerable performance improvement over the conventional detection algorithm. The bit error rate (BER) performance of the proposed detection algorithm is evaluated by the simulation. In the case of 2 transmit and 2 receive antennas, at $BER=10^{-4}$ the proposed algorithm obtains about 3 dB gain over the conventional detection algorithm. The packet error rate (PER), link throughput, and coverage performance of the SF-OFDM WLAN with the proposed detection algorithm are also estimated. For the target throughput at $80\%$ of the peak data rate, the SF-OFDM WLAN achieves the average SNR gain of about 5.95 dB and the average coverage gain of 3.98 meter. The SF-OFDM WLAN baseband processor with the proposed algorithm was designed in a hardware description language and synthesized to gate-level circuits using 0.18um 1.8V CMOS standard cell library. With the division-free architecture, the total logic gate count for the processor is 945K. The real-time operation is verified and evaluated using a FPGA test system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.9
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• pp.46-53
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• 2007

The link-fault recovery in the normal Ethernet bridged networks has relied on the Spanning Tree Protocol(STP) or Rapid STP. However, STP can not offer fast error recovery which is needed real-time services such as aircraft. In this paper, we compare automatic protection switching(APS) providing fault-tolerant function in the BcN back bone system with Avionic Full Duplex Switched Ethernet(AFDX) which is recently equipped in the A380 for Airbone Databuses. Also, we propose a link-bypass scheme for improving fault-tolerant performance of the AFDX by connecting switches and bypass fault section when a fault is originated on the link. For comparing and verifying the performance of proposed scheme, we simulated Ethernet, AFDX, APS and proposed AFDX with link-bypass scheme using NS-2. The proposed AFDX with link-bypass scheme can be applied to aircrafts, BcN backbone networks and industrial automatic networks.