• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38A no.11
• /
• pp.955-966
• /
• 2013

We propose two feedback interference cancellers(FICs) to improve the performance of the equalization digital on-channel repeater(EDOCR) with the FIC for the ATSC DTV broadcasting system. The FIC estimates the feedback channel between Tx. and Rx. antennas of the repeater by cross-correlating the reference signal and the feedback signal. Since there is a DC pilot which ruins the white property of the ATSC DTV signals, the FIC cannot estimate the feedback channel accurately. To solve the problem, the structural method which uses an additional DC pilot free reference for feedback channel estimation and the algorithmic method based on the digital signal processing which whitens the ATSC DTV signals and performs the feedback cancellation in the whitened signal domain. Simulation results show that the proposed two FICs show better feedback cancellation performance than the conventional FIC.

• Journal of Satellite, Information and Communications
• /
• v.3 no.2
• /
• pp.1-6
• /
• 2008

Space-time codes (STC) can achieve the diversity gain in a multi-path environment without additional bandwidth requirement. Recent study results reported that satellite systems can also achieve this diversity gain by using space-time codes in a cooperative network with terrestrial repeaters. Due to uni-directional nature of satellite DMB services, transmit diversity can be considered as one of the most effective ways to improve the performance. In this paper, we demonstrate various simulations results of STC schemes which can contribute to improve performance of future satellite DMB services. The STC schemes introduced in this paper provides diversity gains by combing independent coded signal from the satellite as well as from the terrestrial repeaters. In addition, we discuss a few points which should be considered to develop and implement these STC schemes.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.43 no.1
• /
• pp.72-78
• /
• 2015

Recently, the usage of the satellite is increased more and more in the areas that are communication, weather, marine, optical, radar etc. The functions of the Satellite are evolving from passive transponder to active transponder by the developing of a technology. Advanced countries in satellites install the DCAMP for increase of bandwidth efficiency, improvement of QoS by interference rejection. DCAMP includes many digital components in order to implement functions. Thus, these kinds of active transponders consume much more power compared to passive transponder and then increase the heat. In this paper, we discuss the TVAC test result of DCAMP in EQM(Engineering Qualification Model) level. The paper shows the test results of digital gain control in order to verify DCAMP status under the TVAC test. In addition, the temperature and heat condition of main components from viewpoint of derating will be treated through the official environment test for qualification.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.23 no.4
• /
• pp.1134-1147
• /
• 1998

Remote management and control system for LMDS wireless CATV network which is being developed at SK Telecom is developed. This system is composed of central control division located at head center and remote units for remote transceivers equipped in base stations and repeaters. It monitors the state of the remote transceivers and controls the operations using PSTN for iterface. Remote transceivers whould be equipped in pairs, and the operations are exchanged automatically in case of emergency situations. the remote units are designed not only to perform commands form central control division, bet to inform emergency situations such as disorder and power failure. This system works well, which is established at Central research center in SK Telecom with remote units such as BTX, PPTX, and PPRX. This system could be utilized in other applications requiring remote control through sligh modifications.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.12A
• /
• pp.1260-1266
• /
• 2007

Error propagation of source-relay (S-R) link limits the performance of decode-and-forward (DF) relay and prohibits DF relay from achieving full diversity gain. In order to solve this problem, the proposed deployment strategy focuses on two objectives. One is to achieve full diversity gain, and the other is to minimize the used power of the DF relay system. In order to achieve full diversity, the error probability of S-R link should be lower than that of maximal ratio combining (MRC) at destination without error propagation since the error probability of the weaker link dominates the total error probability. The proposed strategy of relay positioning points out the range of the relay position for achieving full diversity, and the used power of the relay is minimized by this range. Analysis of error probability and simulation results prove that the two objectives are achieved by the proposed strategy of the relay position.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.8B
• /
• pp.1028-1037
• /
• 2011

Recently, Selim et al proposed public key cryptography based privacy preserving multi-context RFID authentication protocol. However Selim et al's proposed protocol not only doesn't fit into passive tag based RFID system because it uses public key based encryption algorithm to perform authentication between reader and tag, but also is insecure to an impersonation attack because it doesn't provide mutual authentication. In order to eliminate the above described efficiency problem and security vulnerabilities, this paper proposes a new multi-context RFID mutual authentication protocol that can prevent privacy invasion and tag impersonation attack through providing mutual authentication between single passive tag which is located different application space and readers which provide multi-context purposes and can secure against relay attack and denial-of-service attack. As a result, the proposed protocol performs secure mutual authentication based on the collected space and time information from the RFID reader and provides strong security and high computation efficiency because if performs secure one-way hash function and symmetric encryption operations suitable to the environments of passive RFID tags.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.18 no.11
• /
• pp.2771-2778
• /
• 2014

In this paper, we propose an algorithm that select efficient relay nodes using information of network environment and nodes. The proposed algorithm can be used changeable weight factors as following network environment in node density. The routing protocols adopting store-carry-forward method are used for solving network problems occurred by unstable end-to-end connection in Delay Tolerant Networks(DTNs). Exiting DTN routing algorithms have problems that large latency and overhead because of deficiency of network informations. The proposed algorithm could be provide a solution this problems using changeable weight factor and prediction of network environment. Thus, selected relay nodes work efficiently in unstable and stressed network environment. Simulation results show that enhancement performance as overhead, delivery ratio, average latency compared to exiting DTN routing algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.3A
• /
• pp.258-264
• /
• 2009

In this paper, we propose an efficient cooperative diversity scheme for mobile satellite multimedia broadcasting services. The proposed scheme is a transmit diversity technique to adapt time varying channel conditions, and we do not need any channel quality information from the return link. In the proposed scheme, we utilize space-time block coding (STBC) and rate compatible turbo codes in order to realize the transmit diversity for the mobile satellite system with several repeaters. The satellite and several repeaters operate in unison to send the encoded signals, so that the receiver may realize diversity gain. The simulation results demonstrate that the proposed scheme can provide highly improved performance.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.1A
• /
• pp.57-65
• /
• 2007

The overlay multicast that has been recently presented as IP alternative for the IP multicast has been getting much persuasion by the computing power of the hardware and the advancement of the network techniques to enforce Routing in application-level. In an overlay multicast, the system resource and the network bandwidth must be utilized efficiently to service real-time HDTV images. Specifically, the system must consider the delay and the jitter that can be incurred at the application-level. In this paper, we implement a server and a client to broadcast HDTV, in the session composed by the existing overlay multicast protocol. The broadcasting server performs the service using a TV tuner, An HDTV camcorder, and files, clients constituting a multicast group relay the received data to other clients. At this time, the information that the clients report periodically, including their delay and the network state, to the server is used as an important information to maintain an overlay session. The implementation is based on the DirectX and its performance is evaluated by the LAN test bed that has been set.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.8 no.3
• /
• pp.523-528
• /
• 2004

The bands 27.5 ∼ 28.35GHz and 31.0 ∼ 31.3GHz were allocated to the High Altitude Platform Station in WRC-2000. However, since these bands were already allocated to the existing fixed-satellite service, the analysis on the interference effects between the existing FSS/GSO system and FS/HAPS system should be needed. To do study on the interference effects between above two systems, we can consider two frequency operational conditions, one is the Reverse mode and the other Forward mode. In this paper, we considered the Forward mode as the frequency operational condition and analyzed the interference effect from a number of GSO satellites to HAPS ground station due to the I/N values, the latitude of HAPS and the satellite separation. In future, these results will be vital data to share between HAPS and GSO systems.