• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.12
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• pp.739-745
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• 2014

It has been shown in compressive sensing that every s-sparse $x{\in}R^N$ can be recovered from the measurement vector y=Ax or the noisy vector y=Ax+e via ${\ell}_1$-minimization as soon as the 3s-restricted isometry constant of the sensing matrix A is smaller than 1/2 or smaller than $1/\sqrt{3}$ by applying the Iterative Hard Thresholding (IHT) algorithm. However, recovery can be guaranteed by practical algorithms for some certain assumptions of acquisition schemes. One of the key assumption is that the sensing matrix must satisfy the Restricted Isometry Property (RIP), which is often violated in the setting of many practical applications. In this paper, we studied a generalization of RIP, called Restricted Biorthogonality Property (RBOP) for anisotropic cases, and the new recovery algorithms called oblique pursuits. Then, we provide an analysis on the success of sparse recovery in terms of restricted biorthogonality constant for the IHT algorithms.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.40 no.5
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• pp.347-356
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• 2003

Camera pose and scene geometry estimation from video sequences is widely used in various areas such as image composition. Structure and motion recovery based on the auto calibration algorithm can insert synthetic 3D objects in real but un modeled scenes and create their views from the camera positions. However, most previous methods require bundle adjustment or non linear minimization process [or more precise results. This paper presents a new auto' calibration algorithm for video sequence based on two steps: the one is key frame selection, and the other removes the key frame with inaccurate camera matrix based on an absolute quadric estimation by LMedS. In the experimental results, we have demonstrated that the proposed method can achieve a precise camera pose estimation and scene geometry recovery without bundle adjustment. In addition, virtual objects have been inserted in the real images by using the camera trajectories.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.4
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• pp.362-372
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• 2000

The causal message logging is a low-cost technique of building a distributed system that can tolerate process crash failures. Previous research in causal message logging protocol assumes that the number of processes in a fault-tolerant system is fixed. This assumption makes all processes modify their data structures when a new process is added or an existing process terminates. However, the proposed approach in this paper allows to each process retain identifiers of only the communicating processes instead of all processes. This mechanism enables the fault-tolerant system to operate at many different scales. Using this mechanism, we develop a new algorithm that can be adapted for recovery in existing causal message logging protocols. Our recovery algorithm is 1) a distributed technique which does not require recovery leader, 2) a nonblocking protocol which does not force live processes to block while recovery is in progress, and 3) a novel mechanism which can tolerate failures of an arbitrary number of processes. Earlier causal message logging protocols lack one or more of the above properties.

• KIPS Transactions on Computer and Communication Systems
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• v.6 no.12
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• pp.487-496
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• 2017

In MySQL InnoDB, there are two ways of storing data. One is to create a separate tablespace for each table and store it separately. Another is to store all table and index information in a single system tablespace. You can use this information to recover deleted data from the record. However, in most of the current database forensic studies, the former is actively researched and its structure is analyzed, whereas the latter is not enough to be used for forensics. Both approaches must be analyzed in terms of database forensics because their storage structures are different from each other. In this paper, we propose a method for recovering deleted records in a method of storing records in IBDATA file, which is a single system tablespace. First, we analyze the IBDATA file to reveal its structure. And introduce delete record recovery algorithm which extended to an unallocated page area which was not considered in the past. In addition, we show that the recovery rate is improved up to 68% compared with the existing method through verification using real data by implementing the algorithm as a tool.

• Journal of KIISE:Information Networking
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• v.32 no.3
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• pp.382-390
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• 2005

As today's networks evolve towards an If-based integrated network, the role of transmission control protocol(TCP) has been increasing as well. As a well-known issue, the performance of TCP is affected by its loss recovery mechanism that is comprised of two algorithms; fast retransmit and fast recovery. Although retransmission timeout(RTO) caused by multiple packet losses can be avoided by using selective acknowledgement(SACK) option, RTO cannot be avoided if a retransmitted packet is lost. Therefore, we propose a simple modification to make it possible for a TCP sender using SACK option to detect a lost retransmission. In order to evaluate the proposed algorithm, simulations have been performed for two scenarios where packet losses are random and correlated. Simulation results show that the proposed algorithm can improve TCP performance significantly.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.12
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• pp.1248-1255
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• 2003

High-speed QPSK demodulator has been one important design objective of any wireless communication systems, especially those offering broadband multimedia service. This paper describes Zero-Crossing IF-level(ZCIF) QPSK demodulator for high-speed wireless communications, and its hardware structures are discussed. ZCIF QPSK demodulator is mainly composed of symbol time circuit and carrier recovery circuit to estimate timing and phase-offsets. There are various schemes. Among them, we use Gardner algorithm and Decision-Directed carrier recovery algorithm which is most efficient scheme to warrant the fast acquisition and tracking to fabricate FPGA chip. The testing results of the implemented onto CPLD-FLEX10K chip show demodulation speed is reached up to 2.6［Mbps］. Actually in case of designing by ASIC, its speed may be faster than CPLD by 5 times. Therefore, it is possible to fabricate the ZCIF QPSK demodulator with speed of 10 Mbps.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.4
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• pp.331-339
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• 2018

The IEEE 1588, commonly known as a precision time protocol (PTP), is a standard for precise clock synchronization that maintains networked measurements and control systems. The best master clock (BMC) algorithm is currently used to establish the master-slave hierarchy for PTP. The BMC allows a slave clock to automatically take over the duties of the master when the slave is disconnected due to a link failure and loses its synchronization; the slave clock depends on a timer to compensate for the failure of the master. However, the BMC algorithm does not provide a fast recovery mechanism in the case of a master failure. In this paper, we propose a technique that combines the IEEE 1588 with network bonding to provide a faster recovery mechanism in the case of a master failure. This technique is implemented by utilizing a pre-existing library PTP daemon (Ptpd) in Linux system, with a specific profile of the IEEE 1588 and it's controlled through bonding modes. Network bonding is a process of combining or joining two or more network interfaces together into a single interface. Network bonding offers performance improvements and redundancy. If one link fails, the other link will work immediately. It can be used in situations where fault tolerance, redundancy, or load balancing networks are needed. The results show combining IEEE 1588 with network bonding enables an incredible shorter recovery time than simply just relying on the IEEE 1588 recovery method alone.

• Journal of Mechanical Science and Technology
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• v.17 no.3
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• pp.409-421
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• 2003

The hierarchical recursive local-correlation PIV algorithm with CBC (correlation based correction) method was employed to increase the spatial resolution of PIV results and to reduce error vectors. The performance of this new PIV algorithm was tested using synthetic images, PIV standard images of Visualization Society of Japan, real flows including ventilation flow inside a vehicle passenger compartment and wake behind a circular cylinder with riblet surface. As a result, most spurious vectors were suppressed by employing the CBC method, the hierarchical recursive correlation algorithm improved the sub-pixel accuracy of PIV results by decreasing the interrogation window size and Increased spatial resolution significantly. However, with recursively decreasing of interrogation window size, the SNR (signal-to-noise ratio) in the correlation plane was decreased and number of spurious vectors was increased. Therefore, compromised determination of optimal interrogation window size is required for given flow images, the performance of recursive algorithm is also discussed from a viewpoint of recovery ratio and error ratio in the paper.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.873-874
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• 2008

In this paper, we propose a packet loss concealment (PLC) algorithm for CELP speech coders, which is based on multiple adaptive codebooks by using comfort noise for the lost packet recovery. The multiple adaptive codebooks are composed of a conventional adaptive codebook to model periodic excitation of speech and another adaptive codebook to provide a better estimate of excitation when packets are lost in the speech onset region. The performance of the proposed PLC algorithm is evaluated by implementing it into the G.729 decoder and compared with that of the PLC algorithm employed in the G.729 decoder by means of perceptual evaluation of speech quality (PESQ). It is shown from the experiments under different burstiness of packet loss rates of 3% and 5% that the proposed PLC algorithm provides higher PESQ scores than the G.729 PLC algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9C
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• pp.1235-1243
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• 2004

In this paper, a new blind equalizer algorithm is proposed which operates on dual mode and combines the benefits of both the Sign-Godard algorithm and the radius-directed algorithm The proposed algorithm has both the properties of good initial convergence of the Sign-Godard algorithm and low residual errors after convergence of the radius-directed algorith High order statistics are used for blind phase recovery and gor avoiding local minima. Simulation results show that the new algorithm has not only faster convergence rated but also lower residual errors than those of the conventional algorithms.