• Journal of Advanced Navigation Technology
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• v.14 no.1
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• pp.33-40
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• 2010

In this paper, the bit-error-ratio (BER) performances of Digital Radio Mondiale Plus (DRM+) system which stand for the European standard to bring analogue FM radio to digital radio in Band-II(30-170 MHz) are evaluated under multipath fading channel models used in Band-II and the adjacent channel interference (ACI) caused by FM signal. From the simulation results, the DRM+ system shows robust performances under time-varying channel environments even though the speed of a vehicle is equal to 300km/h. And it is shown that the frequency diversity, determined by delay spread of multipath fading channel, increases the coding gain of the DRM+ system with an increase of delay spread. In addition, to guarantee the BER performance of 10-4 for DRM+ system with ACI due to FM signal, the simulation results show that the desired signal-to-ACI power ratio must be more than -30 dB when the carrier frequency distance is 150 kHz.

• Journal of Korea Society of Industrial Information Systems
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• v.17 no.7
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• pp.9-16
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• 2012

In order to extend cell coverage and to cope with shadow areas, a relay-assisted wireless communications system has been widely studied. In this paper, we propose new equalization method for single carrier (SC) frequency domain equalizer (FDE) in amplify-and-forward (AF) relaying multi-path networks to improve the performance at shadow areas. The performance of SC-FDE system in 3-slot based multi-path networks can be improved considerably with the diversity gain which we obtain by equalizing the combined signal from relays by means of the minimum mean square error (MMSE) criteria. We find the weighting coefficients of maximum ratio combining (MRC) and the tap coefficients of MMSE equalizer for SC-FDE in AF relaying multi-path networks. Simulation results show that the proposed system considerably outperforms the conventional SC-FDE system.

• Journal of Advanced Navigation Technology
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• v.21 no.6
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• pp.572-578
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• 2017

As the demand of high accuracy positioning for dynamic users increases, Network RTK is actively researched for dynamic users. Network RTK is a system which provides precise positioning in the range of about 50 to 70km radius using carrier phase measurements from several reference stations. By configuring multiple clusters, which provide Network RTK corrections independently, as a single system, it could provide precise positioning for a wider area. In this paper, we have studied how to efficiently operate multiple clusters in the Korean Peninsula. We analyzed the computational load according to the configuration of a multi-cluster system and proposed a method of selecting the main reference station and system infrastructure configuration for efficient operation. In order to analyze the effects of each proposed method, 71 clusters were constructed using the reference stations of the National Geographic Information Institute and simulations were conducted. As a result of the simulation, system computation amount was reduced by 66 % and system configuration cost was reduced by 90 %.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7B
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• pp.583-591
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• 2008

This paper proposes a resource allocation algorithm for minimizing the overall distortion of multiple users in orthogonal frequency division multiplex (OFDM). The proposed algorithm exploits the diversity of multiuser and the rate-distortion function using packet distortion model in a system with limited resources. We first induce a rate-distortion function considering error concealment and error propagation properties of H.264 video structures. Then we perform adaptive resource allocation utilizing multiuser diversity for minimizing the overall video quality degradation. We also consider the proportional rate which is pre-determined for each user. Simulation results show that compared to the previous time division multiple access method and the resource allocation method maximizing data rate, the proposed rate allocation algorithm substantially improves the received video quality.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.12
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• pp.2839-2846
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• 2014

New VHF band for use in VDE is determined by WRC-12 due to the overload of AIS VDL, and the system characteristics of the VDE is recommended as ITU-R M. 1842-1. CS-TDMA, a multiple access method of AIS class B, is recommended as that of the VDE. It is inefficient for CS-TDMA just applying the report interval used in AIS class B to transmit high speed data with higher payload in the aspect of efficiency. In this paper, a simulation is executed in order to determine adequate report interval according to the number of active ships that affects directly network traffic. To this end, the performance of CS-TDMA, which includes the number of received packets, reception success rate, channel utilization, and collision rate, is investigated via a simulation.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.169-180
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• 2023

The performance of underwater acoustic communication is greatly affected by multipath propagation and Doppler spread. This paper proposes a new communication technique, the Triangle Spread Carrier (TSC) technique, by modifying the existing Sweep Spread Carrier (SSC) technique that is strong in a multipath propagation environment. The proposed TSC technique is a form in which the up-chirp and down-chirp signals have repeated carriers, and each correlation function characteristic is used to estimate and correct the Doppler shift frequency of the receiving signal. To demonstrate the performance of the proposed TSC technique, we present the results of simulations using underwater channel simulators and sea trial conducted in the East Sea. When demodulating using only the estimated Doppler shift frequency as a result of the sea trial, the uncoded bit error rate was up to 0.194, but when the proposed method was applied, the uncoded bit error rate was reduced to 0.001.

• Electronics and Telecommunications Trends
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• v.24 no.3
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• pp.24-31
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• 2009

IMT-Advanced 무선전송 시스템 단말모뎀 플랫폼은 다중 반송파 변조 기술, 채널 부호화 기술, 셀 탐색/동기 기술 등 핵심이 되는 요소 기술인 고속 무선 전송 기술을 구현할 수 있는 하드웨어 구조, 기능 및 인터페이스를 설계 제작하였다. 상기 단말모뎀 플랫폼에서는 기저대역 모뎀 물리계층 기능인 변조, 복조, 부호, 복호, 동기를 위한 각각의 FPGA가 실장되는 Daughter Board 형태로 구성되어 L1 기저대역 모뎀 장치에 실장된다. 그리고 PHY 계층(L1)부터 MAE 계층(L2), RRC 계층(L3)까지의 하드웨어 및 소프트웨어 수행을 지원한다. 4G용 단말모뎀을 개발하기 위하여 상용화 이전에 LTE-Advanced 테스트 베드용 단말모뎀 플랫폼을 개발하여 20 MHz 대역폭을 적용 3 km/h의 저속 이동속도에서는 최대 110 Mbps를 수신하고, 최대 55 Mbps를 송신한다. 그리고 120 km/h의 고속 이동속도에서는 최대 55 Mbps를 수신하고, 최대 28 Mbps를 송신한다. 상기 성능을 만족하는 단말모뎀 플랫폼이 개발되면 IMT-Advanced 단말모뎀 플랫폼 기술을 확보하게 된다. 따라서 이동통신 분야에서 기술적인 우위와 시장 선점을 위하여 요소기술 IPR을 확보하고, IMT-Advanced의 표준화 과정에서 이를 국제 표준으로 반영하여 로열티 창출 효과 및 기술 경쟁력을 확보하게 될 것이다. 아울러, LTE 사용자들은 대용량의 고속, 멀티미디어 송 수신을 가능하게 하는 기술로 2010년 이후 가상 현실 서비스, 3D 게임, 센싱 등 사물과 사물이 통신하는 유비쿼터스 서비스로 발전할 것으로 전망한다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2014.06a
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• pp.246-247
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• 2014

케이블 방송망에서 최대 10Gbps 테이터 전송을 위해 최근 북미에서 표준화된 DOCSIS 3.1(Data over Cable Service Interface Specifications Version 3.1)에서는 고차 혼합 변조(Mixed Modulation) 방식을 제시하였다. DOCSIS 3.1 은 하향 데이터 전송을 위해 최대 192MHz 의 대역에서 4K 또는 8K 다중 직교 반송파를 사용한다. 특히 채널 오류 정정을 위한 채널 부호화 방법으로 유럽의 차세대 케이블 방송 표준인 DVB-C2(Digital Video Broadcasting - Cable Version 2)에 정의된 BCH(Bose, Chaudhuri, and Hocquenghem)와 LDPC(Low Density Parity Check) 연접부호를 사용한다. 단, DOCSIS 3.1 에서는 DVB-C2 와 달리 부호율 8/9 의 Short Mode 부호만을 사용하며 최대 16384-QAM 까지 사용한다. 하나의 부호율을 사용하기 때문에 QAM 차수에 따른 요구 SNR 의 차가 크게 된다. 주어진 채널 상황에서 최적의 전송용량을 얻기 위해 QAM 차수에 따른 요구 SNR 의 차를 줄일 수 있는 방법으로 혼합 변조가 도입되었으며, 본 논문에서는 혼합 변조에 따른 수신 성능을 제시한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9C
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• pp.889-896
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• 2006

The crest factor distribution of orthogonal frequency division multiplexing (OFDM) symbol sequences is evaluated and it is shown that OFDM symbol sequences with a short period are expected to have a high crest factor. The crest factor relationship between two input symbol sequences, Hamming distance D apart is also derived. Using these two results, we propose two criteria for a phase sequence set of the selected mapping (SLM) scheme and suggest the rows of the cyclic Hadamard matrix constructed from an m-sequence as the near optimal phase sequence set of the SLM scheme.

• Journal of Advanced Navigation Technology
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• v.10 no.1
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• pp.20-25
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• 2006

In these days, OFDM(Orthogonal Frequency Division Multiplexing) is adopted to support high-speed data communication based on multi-path RF channel, but it has some weak point. One of those is that it has a higher PAR(peak-to-average power ratio) compared with single-carrier method. If some PAR of the transmitted signal is high, nonlinear amplitude distortion has occurred when it pass through the HPA(high power amplifier). There is a solution to prevent nonlinear distortion using higher peak power HPA, but it makes inefficiency and a cost problem. In this paper, we choose the SLM(Selected Mapping) scheme, which transmit the lowest PAR signal after OFDM symbol mapping, in various schemes reducing PAR for OFDM system. And we derived the performances of SLM method in fading channel through computer simulations.