• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.12 no.5
• /
• pp.694-704
• /
• 2001

In this work, We evaluate the performance of eigencanceller which can suppress directional interferences and noise effectively while maintaining specified beam pattern constraints. The constraints and optimal weight vector of eigencanceller vary by using interference and noise or desired signal, interference and noise as array input signal. From the analysis results in the steady state, We show that weight vectors in each case are simplified the form of projection equation that belongs to desired subspace orthogonal to interference subspace and eigencanceller has the better performance than DMI method through mathematical analysis and simulation.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.19 no.6
• /
• pp.161-174
• /
• 2009

IPTV provides their services only for their subscribers who have a eligibility to watch it by using Conditional Access System(CAS). CAS has been servicing their contents for subscribers by using set-top box or cable card so far, but these days, to solve the compatibility between kinds of devices, linkage with other services as DRM and confirming stability, the research of Downloadable CAS(DCAS) is being advanced steadily. On this paper, we analyse the vulnerability of DCAS based on the OpenCable and make up for the vulnerability in DCAS, then proposes to use secure DCAS system for IPTV. Also we show the result of the research and analyse the satisfaction of requirements.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2006.05a
• /
• pp.119-122
• /
• 2006

VoD(Video on Demand) 시스템은 일반적으로 VoD 서버 및 파일 저장장소 등의 제한된 자원 하에서 운용된다. 따라서 VoD 시스템의 QoS(Quality of Service)는 VoD 서버 및 파일 저장장소가 제한된 운용 자원 하에서 클라이언트들에게 안정된 스트림 서비스를 제공함으로써 보장할 수 있다. 즉, VoD 시스템의 QoS를 보장하기 위해서는 클라이언트들의 스트림 서비스 요청이 제한된 운용자원 때문에 VoD 서버로부터 수신이 거부되거나 또는 파일 저장장소로부터 필요한 데이터 서비스를 받는 도중에 연결이 끊어져 손실되는 장애확률(blocking probability)을 최소화해야 한다. 본 연구에서는 VoD 시스템의 QoS 보장에 활용하기 위하여 VoD 시스템의 장애확률을 추정하는 모델을 개발한다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2010.07a
• /
• pp.4-5
• /
• 2010

다중사용자 다중안테나 시스템은 높은 성능 이득을 가지기 때문에 현재 활발히 연구가 진행되고 있다. 그러나 다중사용자 시스템은 필연적으로 간섭이 발생하게 된다. 송신단이 각 수신단의 채널 정보를 완전히 알면 기존의 간섭제거 기법으로 완벽히 간섭을 제거할 수 있지만 제한된 피드백 환경에서는 그럴 수 없다. 제한된 피드백 환경에서는 채널을 양자화 해야 되는데 양자화 기법으로는 벡터 양자화와 스칼라 양자화 기법이 있다. 일반적으로는 벡터 양자화가 스칼라 양자화 보다 성능이 더 좋다고 알려져 있다. 본 논문에서는 벡터 양자화와 스칼라 양자화의 성능을 비교하고 그 차이가 어느 정도 되는 지 실험결과를 통해서 알아보겠다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.8A
• /
• pp.898-908
• /
• 2004

In this paper, we propose a high speed preamble searcher feasible for RACH(Random Access Channel) preamble structure in WCDMA reverse link receiver. Unlike IS-95, WCDMA system uses AISMA(Acquisition Indication Sense Multiple Access) process. Because of the time limit between RACH preamble transmission and AI(Acquisition Indicators), and the restriction on the number of RACH signatures assigned to RACH preamble, fast acquisition indication is required for efficient operation. The preamble searcher proposed in this paper is based on 2-antenna system and has adopted FHT algorithm that has the radix-2 16 point FFT structure. The acquisition speed using FHT is 64 times faster than the conventional method that correlates each signature. Based on their fast aquisition scheme, we improved the acquisition performance by calculating the correlation up to the 4096 chips of the total preamble length. The performance is analyzed by using Neyman-pearson method. The proposed algorithm has been applied for the implementation of WCDMA reverse link receiver modem successfully.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.8 no.6
• /
• pp.173-178
• /
• 2008

With the discontinuation of analog broadcasting in 2012, the cable broadcasters are investing in the conversion to DCATV (Digital Cable TV). DCATV is providing various broadcast of high quality to audiences through paid broadcasting called PPV (Pay Per View). Such services are using various kinds of CASs (Conditional Access System) in order to verify the viewing rights of subscriber. In addition, to respond to the fast changing environment of digital broadcast, not only simple digitalization of broadcast but also services such as PVR (Personal Video Recorder) and VOD (Video On Demand) are provided to subscribers. Because these additional services have many difficult areas to cover with traditional CAS alone, a new plan has become necessary. With the improvement of related regulations in 2008, the test service of IPTV (Internet Protocol TV) which is a broadcast service through the internet started. Because like DCATV, IPTV also sets the real time broadcast and the VOD service as the basic services, the use of appropriate CAS is required. In this study, the CASs for DCATV and IPTV undergo comparative analysis, and the development direction which will benefit both subscribers and broadcasting companies is suggested.

• Journal of KIISE:Information Networking
• /
• v.36 no.6
• /
• pp.471-480
• /
• 2009

One of the principal impediments to the achievement of a scalable access control for a large number of subscribers in a public broadcast is to distribute key update messages reliably to all stateless receivers. However, in a public broadcast, the rekeying messages can be dropped or compromised during the transmission over an insecure broadcast channel, or transmitted to the receivers while it was off-line. In this study, we propose a novel group key management scheme that features a mechanism that allows the legitimate receivers to recover the current group key even if they lose key update messages for long-term sessions using short hint messages and member computation. The performance analysis result shows that the proposed scheme has advantages of the scalable and efficient rekeying compared with the previous reliable group key distribution schemes. The proposed key management scheme targets a conditional access system in a media broadcast where there is no feedback channel from receivers to the broadcasting station.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.9 no.3
• /
• pp.51-58
• /
• 2010

According to dramatic increase of wireless communication demand, more spectrum resources are needed to support considerable and various wireless services, so cognitive radio(CR) was proposed to reuse unused frequency efficiently. Also, FCC revises its policies regarding the usage of the TV white spaces by unlicensed users. CR is an intelligent wireless communication system that is aware of the radio environment and is capable of adapting its operation to the statistical variations. Spectrum sensing is the key task of the CR systems. However, since spectrum sensing performance changes according to the received signal that is received various geography environment, regional characteristics are considered to estimate the path-loss. Therefore, for more accurate analysis and simulation, we demonstrate the spectrum sensing performance of CR system by various method applying Okumura-hata propagation model.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37B no.10
• /
• pp.938-946
• /
• 2012

Interference alignment (IA) is a data transmission technique that achieves the maximum degrees-of-freedom (DoF) in the multiuser interference channel for high signal-to-noise ratios (SNRs). However, most prior works on IA are based on the unrealistic assumption that perfect and global channel-state information (CSI) is available at all transmitters and receivers. In this paper, we propose the efficient design of feedback framework for IA that substantially suppresses the feedback overhead. While the feedback overhead in the conventional IA quadratically increases with K, the proposed feedback scheme supports the sequential exchange of computed IA precoders between transmitters and receivers and reduces the feedback overhead that linearly scales with K. Moreover, we analyze the residual interference due to the quantization error in limited feedback and propose the ordered IA algorithm that selects IA pair to minimize the sum residual interference in given channel realizations.

• Journal of Broadcast Engineering
• /
• v.20 no.4
• /
• pp.598-605
• /
• 2015

Effective alerts will drastically mitigate the disaster impacts. One way to enhance the effectiveness is to prepare multiple alert distribution channels. In this paper, we propose a new emergency alert distribution system that will solve the weaknesses of the current distribution systems, such as Cell Broadcasting System and T-DMB Automatic Emergency Alert Service. The weaknesses are: the limitation of message length, small portions of terminals that can receive and display the alert signal, and one-way communication service. To solve these problems, we propose an emergency alert distribution system over the Internet with RSS (Rich Site Summary) format. The system also has the capability of adaptive alert filtering according to the receiver characteristics. We analyzed the characteristics of RSS as an alerting format, and draw functional requirements satisfying use case scenarios. We designed the system only with major requirements and verified it on our test bed. Sending richer message contents through various receiving terminals, the system will achieve more effective emergency alert service.