• Journal of the Korea Society of Computer and Information
• /
• v.19 no.1
• /
• pp.77-84
• /
• 2014

In this paper, we propose the hierarchical network synchronization scheme that is backward compatible for the existing commercial system, efficient for total system performance, and whose hardware modification is minimized. This system performance is, the relationship among bandwidth efficiency, complexity and MODEM performance, and superiority of network system applicability. The proposed structure can remedy the high hardware complexity and the lower accuracy of network sychronization that the existing satellite communication terminal system in the star network based on TDM/MF-TDMA of DVB-S2/RCS standards has. Besides, It has high efficiency in view of cost and system performance if the system designed for satellite broadcast requires system upgrade. In the body section, its hardware complexity and system performance of the proposed algorithm is analysed theoretically and treated with the related parameters(symbol rate, spreading factor, etc.) and the BER performance of control channel through the computer simulation for its verification that it can be applied for communications system.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.42 no.2 s.302
• /
• pp.59-68
• /
• 2005

The amount of digitalized contents has been rapidly increased, but the main distribution channel of them is Internet which is easily accessible. Therefore 'security' necessarily arises as one of the most important issues and the method of protecting contents becomes a major research topic as much as data coding techniques. In recent years, many developers have studied on techniques that allow only authorized person to access contents. Among them the scrambling method is one of well-known security techniques. In this paper, we propose a simple and effective digital video scrambling method which utilizes the intra block properties of a recent video coding technique, H.264. Since intra prediction modes are adopted in H.264 standard, it is easy to scramble a video sequence with modification of the intra prediction modes. In addition to its simplicity, the proposed method does not increase bit rate after scrambling. The inter blocks are also distorted by scrambling intra blocks only. This paper introduces a new digital video scrambling method and verifies its effectiveness through simulation.

• Journal of IKEEE
• /
• v.4 no.2 s.7
• /
• pp.257-265
• /
• 2000

Turbo Code decoder is an iterate decoding technology, which extracts extrinsic information from the bit to be decoded by calculating both forward and backward metrics in each decoding step, and uses the information to the next decoding step. Viterbi decoder, which is for a convolutional code, runs continuous mode, while Turbo Code decoder runs by block unit. There are algorithms used in a decoder : which are MAP(maximum a posteriori) algorithm requiring very complicated calculation and SOVA(soft output Viterbi algorithm) using Viterbi algorithm suggested by Hagenauer, and it is known that the decoding performance of MAP is better. The result of this make experimentation shows that the performance of SOVA, which has half complex algorithm compare to MAP, is almost same as the performance of MAP when the SOVA decoding performance is supplemented with Robust equalization techniques.

• The Journal of Information Technology
• /
• v.5 no.1
• /
• pp.157-171
• /
• 2002

The evolution of transaction-based business model is upon us. The business models of many e-Marketplace in their early stages have typically been based on transaction fees. Many e-Marketplaces have even called out transaction revenues as a core element of their business plans. The transaction business represents the most simple of business models, but it does not provide a long-term sustain able advantage. For buyer's convenience, wide selection and test price hold appeal. For suppliers, the extended global market reach and direct access to customers and consortiums of customers is powerful. To maxmize leverage of these new e-marketplace, you must from both a buyer perspective as well as a supplier perspective. Also required is a strategy that takes in account all of the various e-Marketplace transaction standards and one that allows the easy accomodation to new e-marketplace as the market change. These new e-marketplace will need to be factored into the sales channel strategies. To be successful, integration with these e-marketplaces should occur at a complete business process level. This study explored independent and industry-backed current and future business models that are emerging in the B2B electronic market industry, as well as value -added service models for the Net market maker industry. E-Marketplaces will evolve into digital work environments in which real industry collaboration can occur.

• International Commerce and Information Review
• /
• v.7 no.3
• /
• pp.195-212
• /
• 2005

International trade has been changed from traditional trade to e-trade due to the fast expanding of information technology like e-marketplace, EDI (Electronic data interchange) using Internet since mid of 1990's. e-Trade, as a new trade method, could handle every trade procedure such as market research, contract, customs clearance, logistics and payment using IT like internet without restriction of time and space. The evolution of transaction-based business model is upon us. The business models of many e-Marketplace in their early stages have typically been based on transaction fees. Many e-Marketplaces have even called out transaction revenues as a core element of their business plans. The transaction business represents the most simple of business models, but it does not provide a long-term sustain able advantage. For buyer's convenience, wide selection and test price hold appeal. For suppliers, the extended global market reach and direct access to customers and consortiums of customers is powerful. To maximize leverage of these new e-marketplace, you must from both a buyer perspective as well as a supplier perspective. Also required is a strategy that takes in account all of the various e-Marketplace transaction standards and one that allows the easy accomodation to new e-marketplace as the market change. These new e-marketplace will need to be factored into the sales channel strategies. To be successful, integration with these e-marketplaces should occur at a complete business process level. This study would suggest on the role of buyers and sellers for e-trade which could maximize effect of e-trade in order to cope with rapid changing IT environment and global trade environment. Therefore, this study suggests top priority tasks for implementing on the specialization strategy of e-trade process.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.9 no.6
• /
• pp.1167-1173
• /
• 2005

In this paper, the use of an antenna array is considered for code timing acquisition of DS-CDMA signals. The probabilities of acquisition are evaluated by applying multiple narrow fixed-beams to the conventional MUSIC acquisition approach in the multiuser environment on the time-varying Rayleigh fading channel. Each fixed-beam for spatial filtering is dedicated to an individual angular sector that is formed by dividing the entire angular domain by the number of antenna elements. The fixed-beams with a capability of interference suppression provide the additional degrees of freedom,. Hence, the multibeam-based MUSIC estimator can be used to synchronize to more users than the conventional MUSIC algorithm for one antenna. The multibeam-based subspace method is evaluated to significantly improve the performance of a single antenna based MUSIC technique in multiuser scenarios.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.10 no.5
• /
• pp.910-920
• /
• 2006

We consider the problem of estimating a code-timing of DS-CDMA signal in antenna array systems in the presence of flat fading channels and near-far environments. We derive an approximate maximum likelihood algorithm of estimating the code-timing of a desired user for DS-CDMA systems to better utilize the time-varying characteristics of the fading process. In the development of code timing estimator, the given observation bits are divided into many sets of sub-windows with each sufficiently large. The proposed method uses sub-windows with equal size associated with the coherence time of channel fading. The alternative approach is that without the estimation of the fading rate, the sufficiently given observation bits are simply separated into two consecutive sets of sub-windows. The derivation of the proposed algorithms is based on multiple antennas partially correlated in space. The impacts of spatial fading correlation on acquisition and men acquisition time performance of the proposed algorithms are also examined.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.21 no.10
• /
• pp.1873-1878
• /
• 2017

Recently, many researches have been conducted on the aviation industry to replace the wire harness cable between the avionics of the aircraft with the wireless network. In this paper, we present an Event-Based Simulator for Wireless Avionics Intra-Communications (ES-WAIC) that can verify core technologies of wireless networks and efficiently integrate different layers of the network. ES-WAIC is developed to enhance the readability between the real time control application developers of the higher layer and the network layer developers. Specifically, the practical implement relies on an event-based programming concept to increase portability and compatibility that can be applied to the realistic low-power wireless embedded networks. ES-WAIC implements the overall system layers including the wireless channel modeling of the 4.4GHz band, the physical layer, the medium access control, the network, and the application layer of wireless avionics intra-communications.

• Journal of Communications and Networks
• /
• v.7 no.2
• /
• pp.144-156
• /
• 2005

Video streaming over wireless networks is challenging due to node mobility and high channel error rate. In this paper, we propose a multi-source video streaming (MUVIS) system to support high quality video streaming service over IEEE 802.1l-based wireless networks. We begin by collocating a streaming proxy with the wireless access point to help leverage both the media server and peers in the WLAN. By tracking the peer mobility patterns and performing content discovery among peers, we construct a multi-source sender group and stream video using a rate-distortion optimized scheme. We formulate such a multi-source streaming scenario as a combinatorial packet scheduling problem and introduce the concept of asynchronous clocks to decouple the problem into three steps. First, we decide the membership of the multisource sender group based on the mobility pattern tracking, available video content in each peer and the bandwidth each peer allocates to the multi-source streaming service. Then, we select one sender from the sender group in each optimization instance using asynchronous clocks. Finally, we apply the point-to-point rate-distortion optimization framework between the selected sender-receiver pair. In addition, we implement two different caching strategies, simple caching simple fetching (SCSF) and distortion minimized smart caching (DMSC), in the proxy to investigate the effect of caching on the streaming performance. To design more realistic simulation models, we use the empirical results from corporate wireless networks to generate node mobility. Simulation results show that our proposed multi-source streaming scheme has better performance than the traditional server-only streaming scheme and that proxy-based caching can potentially improve video streaming performance.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.7 no.12
• /
• pp.2957-2986
• /
• 2013

The traditional approach of fixed spectrum allocation to licensed networks has resulted in spectrum underutilisation. Cognitive radio technology is envisioned as a promising solution that can be used to resolve the ineffectiveness of the fixed spectrum allocation policy by accessing the underutilised spectrum of existing technologies opportunistically. The implementation of cognitive radio networks (CRNs) faces distinct challenges due to the fact that two systems (i.e., cognitive radio (CR) and primary users (PUs)) with conflicting interests interact with each other. Specially, in self-organised systems such as ad-hoc CRNs (AHCRNs), the coordination of spectrum access introduces challenges to researchers due to rapid utilisation changes in the available spectrum, as well as the multi-hop nature of ad-hoc networks, which creates additional challenges in the analysis of resource allocation (e.g., power control, channel and rate allocation). Instead, game theory has been adopted as a powerful mathematical tool in analysing and modelling the interaction processes of AHCRNs. In this survey, we first review the most fundamental concepts and architectures of CRNs and AHCRNs. We then introduce the concepts of game theory, utility function, Nash equilibrium and pricing techniques. Finally, we survey the recent literature on the game theoretic analysis of AHCRNs, highlighting its applicability to the physical layer PHY, the MAC layer and the network layer.