• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.22 no.3
• /
• pp.513-519
• /
• 2018

OFDM modulation has been used for a transmission scheme in 4G LTE (Long Term Evolution) and Wi-Fi systems to mitigate the effects of frequency selective fading channels. An OFDM modulation is a block transmission scheme because an OFDM symbol consists of multiple subcarriers with narrow bandwidth. Therefore, all OFDM symbols in a frame should be filled out with data and padding bits. Depending on the amount of data, more padding bits than information bits can occupy the last OFDM symbol. Such inefficiency causes the loss of throughput. To overcome this problem, an efficiency padding method is proposed by using the property of DFT (Discrete Fourier Transform). In the proposed method, symbol duration of the last symbol is changed depending on the number used data subcarriers in the last symbol. With numerical evaluation, it is examined that throughput enhancement achieved by the proposed method can be about 20% depending a transmission scheme and data length.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2005.05a
• /
• pp.643-646
• /
• 2005

본 논문에서는 IP 통신망의 특성을 고려하여 IP 망 기반의 방송 서비스를 위한 효율적인 EPG 데이터 전송 방안을 제안한다. EPG 정보를 사용자 요구 특성을 고려하여 여러 그룹으로 분할하고 이에 대해 OOB 채널을 통한 멀티캐스트 전송 방식과 사용자 별 요구 및 응답 처리를 통한 유니캐스트 전송 방식을 혼합 적용한다. 또한 서비스 요구 상황에 따라 두 방식을 동적으로 선택 및 변경함으로써 EPG 시스템의 서버 자원과 네트워크 대역폭을 효율적으로 활용할 수 있다.

• Information and Communications Magazine
• /
• v.24 no.8
• /
• pp.59-70
• /
• 2007

차세대 이동 통신 시스템은 다양한 응용 분야들을 지원하기 위하여 광대역을 사용한 고속 데이터 전송이 가능해야 할 것이다. 이와 같은 요구 사항을 효율적으로 대처할 수 있는 중요한 전송 방식중의 하나가 OFDM (Orthogonal frequency division multiplexing) 기법이며, 여러 국제 표준단체에서 차세대 전송 방식의 중요 후보로써 채택하여 심도깊은 연구가 진행되고 있는 실정이다. 본 고에서는 OFDM 전송 방식의 기본적인 특징을 살펴보고, OFDM 시스템 상에서 동기 획득 (Synchronization) 및 채널 추정 (Channel estimation)을 위하여 사용될 수 있는 기본적인 알고리즘들에 대하여 간략히 소개하고 그 특징을 살펴본다.

• Proceedings of the Korean Information Science Society Conference
• /
• 2003.04a
• /
• pp.181-183
• /
• 2003

본 논문에서는 적응적인 스트리밍 시스템 환경에서 계층적으로 압축된 멀티미디어 데이터의 저장구조와 자료인출 원리를 분석한다. 또한 네트워크 시뮬레이션을 이용, 네트워크 상에서 다양한 멀티미디어 스트리밍 부하의 특성을 분석한다. 두 가지 분석을 통해 기존의 멀티미디어 저장방식이 다양한 네트워크 환경과 시간에 따라 전송율이 변화하는 적응적 스트리밍 시스템의 요구를 충족시키지 못한다는 것을 확인한다. 이를 개선하기 위해 제안된 하모닉 인터리빙은 하모닉 인터리빙 방식은 전송비율이 높은 멀티미디어 데이터 블록의 위치를 연속적으로 배치하기 위해서 전송비율이 높은 계층과 그렇지 않은 계층을 별도의 그룹으로 나누어서 저장하는 방식이다. 실험을 통해서 네트워크 상황이 전송하고자 하는 영화의 대역폭을 보장하지 못하는 환경에서는 기존의 저장방식보다 새로 제안된 저장방식이 디스크 사용율에 있어 우수한 성능을 나타냄을 보인다.

• ETRI Journal
• /
• v.7 no.4
• /
• pp.31-36
• /
• 1985

R2 신호 방식은 전자 교환국간에 사용되는 신호 방식으로서 종래의 decadic신호 방식에 비해 signalling속도, 신호전송 신뢰도, 전송 정보의 양에 있어서 큰 장점을 갖는다. 본고에서는 당 연구소에서 개발한 전전자 교환기 TDX-1 에 실현된 R2 신호 방식의 포로세서간 처리구조 및 소프트웨어에 대해서 기술하였다. 또한 현장 운용시 다른 교환국과의 신호 정합에서 발생된 몇가지 문제점 및 해결방안을 제시하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.47 no.7
• /
• pp.29-35
• /
• 2010

The cooperative transmission between sectors in next generation communications standards, e.g., 3GPP LTE-Advanced and IEEE 802.16m, has become an important research issue. Hence methods to decide the optimal antenna tilting angle in cooperative transmission between sectors are needed. This paper proposes methods to decide the optimal antenna tilting angle in cases of non-cooperative and cooperative transmissions between sectors. The proposed methods use an objective function that maximizes the cell average log rate or the cell average rate for users distributed uniformly within the radius of the sector. Also, the objective function which maximizes the cell average rate determined by adaptive modulation and coding (AMC) used in actual cellular systems is considered. When the cell average rate becomes the objective function, the system rate efficiency increases significantly for both cooperative and non-cooperative transmission. When the cell average log rate and the AMC rate become the objective functions, an optimal antenna tilting decision method which effectively increases the efficiency of cell boundary users is discussed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.1
• /
• pp.14-20
• /
• 2012

CoMP(Coordinated Multi-Point transmission and reception) refers to a cooperative transmission strategy to control the interference from adjacent base stations in cellular mobile communication systems, which efficiently enhances the data throughput of the systems. As the number of the base stations participating in cooperative transmission increases, however, a larger amount of information exchange to carry the CSI(Channel State Information) of the mobile terminals is required. In this paper, we propose a partial CoMP transmission method for systems under the constraint of finite feedback information data. This method selects candidates of base stations which can provide high efficiency gain when they participate in the CoMP set. To achieve this, the cooperative base station combination is constructed by considering the preferred base stations of users. The cooperative base station combinations are dynamically applied since the preferred base station combinations of users may be different. We perform computer simulations to compare performance of the non-CoMP, full-CoMP and partial CoMP in terms of the average throughput using finite feedback and demonstrate the performance improvement of the proposed method.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.5 no.2
• /
• pp.251-256
• /
• 2001

In this study, a OFDM mode, unlike traditional single carrier mode, is that a great number of carrier in multi-channel environment is transmitted by modulating objective Data parallel in order to execute high speed Data translation and make frequency orthogonal to offer high spectrum efficiency As a result, this method is adopted to a variety of fields and is being actively studied. In this papers, the efficiency of OFDM wireless-communication systems is evaluated by modulation methods through computer simulation. M-PSK and M-QAM are used as modulation methods. The simulation is executed in a real channel and a virtual channel included multi-path, AWGN, Peak Power clipping, Frame Start Time Error. As a result of simulation, it is confirmed that M-OAM method is superior to M-PSK in OFDM systems in terms of the transmission methods.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.3B
• /
• pp.196-201
• /
• 2002

OFDM(orthogonal Frequency Division Multiplex) modulates transmitting data with many carriers in parallel. As a result, high-speed data transmission is carried out and high spectral efficiency is provided by overlapping orthogonal frequencies. Therefore, OFDM is applied to many communication systems. In this paper, according to modulation methods(M-PSK and M-QAM), coded-OFDM wireless communication is simulated. Turbo code is used and two channels(virtual and real channel) are used. both channels have multipath delay spread, Gaussian noise, and peak power clipping. As a result of the simulation, coding gain is about 3dB and it is proved that M-QAM modulation is better than M-PSK. Start after striking space key 2 times.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.5B
• /
• pp.449-455
• /
• 2006

Due to advance in multimedia applications and integrated Internet services, the optical access networks have been actively studied. In particular, Ethernet passive optical network (EPON) has received much attention due to high bandwidth provision with low cost. In EPON system, the data transmission is carried out in two directions: downstream (from OLT to ONU) and upstream (from ONU to OLT). The downstream data is broadcasted to every ONUs, while the upstream data is point-to-point transmitted between each ONU and OLT, where the uplink is shared by all ONUs in the form of TDMA. The bandwidth allocation algorithm is required to efficiently manage the bandwidth on the uplink. The limited algorithm was proposed to enhance the capability of dynamic bandwidth allocation. In this paper, we propose the adaptive limited algorithm to enhance the shortcomings of limited algorithm. The adaptive limited algorithm enhances the dynamics on bandwidth allocation, and at the same time controls the fairness on packet delay. Through the computer simulations, it is shown that the adaptive limited algorithm achieves high dynamic on bandwidth allocation, maintains a good fairness on packet delay between ONUs, and keeps the fairness on the bandwidth on the demand basis.