• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.7 no.3
• /
• pp.201-210
• /
• 1996

In this paper, we analyzed performance of a symbol timing recovery scheme for 16QAM Radio system. As a symbol timing recovery scheme, both maximum amplitude method(MAM) and wave difference method(WDM) are analyzed employing a pulse shaping filter, such as raised cosine filter(RCF) and nonlinear filter(NLF). Simulation result shows that the jitter performance of MAM or WDM using NLF is better than that using square root RCF. In order to estimate and compensate for the Rayleigh fading PSAM(Pilot Symbol Assisted Modulation) and space diversity are also employed. Consequently, BER performance of about $10^{-4}$ is obtained for $E_b/N_o$= 20 dB.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.25 no.5A
• /
• pp.634-640
• /
• 2000

This paper proposes a new extended decision directed-decision estimated phase recovery algorithm based on maximum likelihood parameter estimation for OQPSK. In this scheme, comparing conventional one, the data dependent noise of phase recovery loop is reduced by inserting filter with 2 taps to in-phase and quadrature-phase channel respectively before phase detector. The proposed scheme is compared to conventionalscheme and OQPSK in aspect to BER(Bit Error Rate) and phase error according to the roll-off factor of baseband filter, the output back-offs of nonlinear satellite channel, and loop bandwidth.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.10 no.7
• /
• pp.2936-2951
• /
• 2016

An emerging satellite technology, Operationally Responsive Space (ORS) is expected to provide a fast and flexible solution for emergency response, such as target tracking, dense earth observation, communicate relaying and so on. To realize large distance transmission, we propose the use of available relay satellites as relay nodes. Accordingly, we apply software defined network (SDN) technology to ORS networks. We additionally propose a satellite network architecture refered to as the SDN-based ORS-Satellite (Sat) networking scheme (SDOS). To overcome the issures of node failures and dynamic topology changes of satellite networks, we combine centralized and distributed routing mechanisms and propose a fast recovery routing algorithm (FRA) for SDOS. In this routing method, we use centralized routing as the base mode.The distributed opportunistic routing starts when node failures or congestion occur. The performance of the proposed routing method was validated through extensive computer simulations.The results demonstrate that the method is effective in terms of resoving low end-to-end delay, jitter and packet drops.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2021.10a
• /
• pp.661-663
• /
• 2021

Network performance is degraded when the UE is disconnected because the outage occurs at the base station in a mobile communication system. Therefore it is important to detect and recover the outage. In this paper, detecting the outage base station by using the KPI and the network scanning in the neighbor base station, and increasing the transmit power and changing the frequency band to recovery the outage scheme is proposed. The proposed scheme uses not only the KPI of the base station but also the network scanning of the neighbor base stations to detect the outage base station, so that it is possible to detect the outage base station more accurately. In addition, when the outage occurred, the neighbor base station changes the transmit power and frequency band to recover the outage with less signal interference.

• Journal of Broadcast Engineering
• /
• v.19 no.2
• /
• pp.184-194
• /
• 2014

The CBS methodology has been utilized in order to make a rapid broadcast of emergency alert based on cellular systems. We present a synchronous cooperative communication method for the CBS. Especially, we suggest a synchronization scheme and a data recovery approach for high-rate cooperative communications. For the high-rate transfer of emergency alert, the cyclic prefix is added to the preamble for the synchronization. For the data recovery, the Alamouti technique is utilized on frequency domain, which is similar to SC-FDE. The simulation results confirm that our proposed scheme is very suitable for the CBS.

• ETRI Journal
• /
• v.34 no.4
• /
• pp.645-648
• /
• 2012

An incremental subspace learning scheme to recover lost speech segments online is presented. Our contributions in this work are twofold. First, the recovery problem is transformed into an interpolation problem of the time-varying gains via nonnegative matrix factorization. Second, incremental nonnegative matrix factorization is employed to allow online processing and track the evolution of speech statistics. The effectiveness of the proposed scheme is confirmed by the experiment results.

• Journal of the Korea Society of Computer and Information
• /
• v.22 no.6
• /
• pp.1-8
• /
• 2017

In this paper, we propose a fault tolerance technique which enables embedded systems to run without interruption while its operating system and tasks fail. In order to improve reliability, the proposed scheme makes an embedded system run as a virtual machine on virtual machine monitor. It also prepares a contingency virtual machine at which periodical backups of the embedded system are saved. When an error occurs in the main virtual machine, the corresponding standby virtual machine takes a role of the main virtual machine and continues its operation. Especially such backups and switches of virtual machines are performed with minor performance degradation by manipulating page table entries in virtual machine monitor. By conducting performance evaluation studies, we show that the proposed scheme makes embedded system robust against errors while it does not degrade the performance of the system significantly.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.67 no.4
• /
• pp.208-213
• /
• 2018

In this paper, we studied the control strategy of applying STATCOM(static synchronous compensator) to mitigate the FIDVR(fault induced delayed voltage recovery) phenomenon. The proportion of motor loads is gradually increasing which might affect power system stability. Excessive reactive power consumption by the stall of the motor loads causes FIDVR phenomenon. In addition, the low inertia of the small HVAC(heating, ventilation and air conditioner) unit will not separate itself in the event of a contingency, causing system instability. For this reason, we have developed a control strategy that utilizes STATCOM efficiently through static and dynamic analysis. Case studies on a Korean power system have validated the performance of the proposed scheme under severe contingency scenarios. The results have verified that the proposed strategy can effectively mitigate FIDVR and improve the stability and reliability of the system.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.24 no.11
• /
• pp.1558-1561
• /
• 2020

In this paper, we propose a blockchain scheme to enhance fault tolerance in distributed storage blockchain systems. Traditional blockchain systems suffer from ever-increasing storage cost. To overcome this problem, distributed storage blockchain techniques have been proposed. Distributed storage blockchain schemes effectively reduce the storage cost, but there are still limitations in reducing recovery cost and fault tolerance. The proposed approach recovers multiple errors within a group by utilizing locally repairable codes with availability. This improves the fault tolerance of the blockchain systems. Simulation results show that the proposed scheme enhances the fault tolerance while minimizing storage cost and recovery cost compared to other state-of-art schemes.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2009.11a
• /
• pp.349-350
• /
• 2009

In this paper, we describe an error concealment techniques based on image inpainting for the image impairments due to the packet loss. Image inpainting is to remove or restore the damaged sections from the images, which is usually old images, paintings, or video films. Inpainting has a long history which goes back to the era when the paintings come out. Manual inpainting is no more used, and we can use digital inpainting for the digitally impaired images and video sequences. In this paper, we review the error concealment techniques for the packet loss recovery and propose our inpainting based image impairment recovery scheme for video communication over packet networks.