• ETRI Journal
• /
• v.29 no.5
• /
• pp.596-606
• /
• 2007

It is well known that an OFDM receiver is vulnerable to synchronization errors. Despite fine estimations used in the initial acquisition, there are still residual synchronization errors. Though these errors are very small, they severely degrade the bit error rate (BER) performance. In this paper, we propose a residual error elimination scheme for the digital OFDM baseband receiver aiming to improve the overall BER performance. Three improvements on existing schemes are made: a pilot-aided recursive algorithm for joint estimation of the residual carrier frequency and sampling time offsets; a delay-based timing error correction technique, which smoothly adjusts the incoming data stream without resampling disturbance; and a decision-directed channel gain update algorithm based on recursive least-squares criterion, which offers faster convergence and smaller error than the least-mean-squares algorithms. Simulation results show that the proposed scheme works well in the multipath channel, and its performance is close to that of an OFDM system with perfect synchronization parameters.

• Journal of Communications and Networks
• /
• v.7 no.1
• /
• pp.1-12
• /
• 2005

Ethernet is being deployed in metropolitan area networks (MANs) as a lower-cost alternative to SONET-based infrastructures. MANs are usually required to support common communication services, such as voice and frame relay, based on legacy synchronous TDM technology in addition to asynchronous packet data transport. This paper addresses the clock synchronization problem that arises when transporting synchronous services over an asynchronous packet infrastructure, such as Ethernet. A novel algorithm for clock synchronization is presented combining time-stamp methods used in the network time protocol (NTP) with signal processing techniques applied to measured packet interarrival times. The algorithm achieves the frequency accuracy, stability, low drift, holdover performance, and rapid convergence required for viable emulation of TDM circuit services over Ethernet.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2009.11a
• /
• pp.189-190
• /
• 2009

For applications involving the monitoring of large areas, dense sensor networks are not practical. For such applications, delay tolerant networks which consist of disconnected clusters of sensors that are visited periodically by a mobile robot are implemented. Because clock synchronization is critical to any data collection endeavor, and because the structure of DTNs is unique, this paper examines various clock synchronization algorithms as they apply to DTNs. A simulation tool was developed to examine and evaluate the RBS clock synchronization algorithm for DTNs.

• Proceedings of the IEEK Conference
• /
• 2005.11a
• /
• pp.967-970
• /
• 2005

The Music Player MAF Player Format of ISO/IEC 23000-2 FDIS consists of MP3 data, MPEG-7 metadata and one optional JPEG image data based on MPEG-4 File Format. However, the current Music Player MAF format does not allow multiple JPEG image data or timed text data. It is helpful to use timed text data and multiple JPEG images in the various multimedia applications. For example, listening material for the foreign language needs an additional book which has text and images, the audio contents which can get image and text data can be helpful to understand the whole story and situations well. In this paper, we propose the detailed file structure in conjunction with MPEG-4 File Format in order to improve the functionalities, which carry multiple image data and text data with synchronization information between MP3 data and other resources.

• Journal of the Korea Computer Graphics Society
• /
• v.18 no.1
• /
• pp.23-28
• /
• 2012

In this paper, we present a new method for automatically synchronize captured facial expression data with its corresponding motion data. In a usual optical motion capture set-up, a detailed facial expression can not be captured simultaneously in the motion capture session because its resolution requirement is higher than that of the motion capture. Therefore, those are captured in two separate sessions and need to be synchronized in the post-process to be used for generating a convincing character animation. Based on the patterns of the actor's neck movement extracted from those two data, we present a non-linear time warping method for the automatic synchronization. We justify our method with the actual examples to show the viability of the method.

• Journal of Institute of Control, Robotics and Systems
• /
• v.13 no.12
• /
• pp.1198-1206
• /
• 2007

It is common to use PC or Digital picture frame in stand-alone fashion to view images, movies, or to listen MP3 musics which are considered as multimedia contents, However, such existing methods have weakness for expanding network requirements or augmenting extra data, in such case inevitably requiring external devices. With keeping in mind for such expansion, in this study, we have suggested a new concepts of network module which may utilize an image server for data transmission, in the proposed module, data alarm packet was defined for alerting incoming data from the image server and it became possible to synchronize between the image server and device not only in wired but also in wireless environments through UART. The method consists of a control module for an image server and a synchronization module between the server and the device. We have also tested the feasibility for future commercial usages such as advertisements through performance evaluations.

• The KIPS Transactions:PartC
• /
• v.19C no.3
• /
• pp.209-214
• /
• 2012

Time synchronization is important role in a network, especially in Wireless Sensor Network (WSN) which is required for time-critical applications such as surveillance, tracking, data fusion and scheduling. Time synchronization in WSN should meet the other different requirements than the one in other networks because WSN has critical resource constraints, especially power consumption. This paper presents a new time synchronization scheme for WSN, which is energy efficient by reducing communication overhead. Simulation test shows this new scheme has better energy efficiency and performance of accuracy than existing schemes proposed previously.

• Journal of Satellite, Information and Communications
• /
• v.9 no.3
• /
• pp.80-85
• /
• 2014

In this paper, we propose and analyze a novel synchronization scheme for ubiquitous home network system. In ubiquitous home network system, synchronization method is very important because many consumer electronic devices send the data simultaneously to each other through infrastructure such as access point. We employ digital watermarking sequence to improve synchronization performance without system overhead. The performance of proposed scheme is analyzed in terms of correlation performance. The results of the paper can be applied to design of various applications for ubiquitous home network systems.

• Journal of the Korea Computer Industry Society
• /
• v.3 no.9
• /
• pp.1251-1260
• /
• 2002

Real-time application programs have synchronization constraints which need to be met between media-data. Synchronization method represents feedback method including virtual client-side buffer. This buffer is used in buffer level method. It is client-leading synchronization that is absorbing variable transmission delay time and that is synchronizing by feedback control. It is the important factor for playback rate and QoS if the buffer level is normal or not. To solve the problems, we can control the start of transmission in multimedia server by appling filtering, control and network evaluation function. Synchronization method is processing for smooth presentation without cut-off while media is playing out. When audio frame which is master media is in high threshold buffer level we decrease play out time gradually, otherwise we increase it slowly.

• Journal of Korea Multimedia Society
• /
• v.15 no.11
• /
• pp.1391-1398
• /
• 2012

Time synchronization is crucial in wireless sensor networks such as Wireless USB and WBAN for diverse purposes from the MAC to the application layer. This paper proposes online clock skew estimators to achieve energy-efficient time synchronization for wireless sensor networks. By using recursive least squares estimators, we not only reduce the amount of data which should be stored locally in a table at each sensor node, but also allow offset and skew compensations to be processed simultaneously. Our skew estimators can be easily integrated with traditional offset compensation schemes. The results of simulation and experiment show that the accuracy of time synchronization can be greatly improved through our skew compensation algorithm.