• The Korean Journal of Emergency Medical Services
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• v.23 no.1
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• pp.125-134
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• 2019

Purpose: The aim of this study was to evaluate the usefulness of video communication with medical staff located at a remote location, through a communication application connected to a long term evolution (LTE) mobile communication network in a moving ambulance. Methods: In this study, we recruited patients who were transferred by mobile intensive care unit ambulance from one hospital to another. In the moving ambulance, the information of the patient was transferred to a physician using the application in real time. Recorded video files were evaluated by emergency physicians with experience in video direct medical control. Results: A total of 18 patients were evaluated, and the average score was 5.9 out of a possible 9. It was expected that applying the use of the technology to actual clinical sites would enable the sites to provide assistance. Conclusion: In this study, we confirmed the possibility of benefiting from the clinical field when using the video-audio communication application which is connected to the remote location in real time through the current LTE mobile communication network in the ambulance.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.05a
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• pp.197-199
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• 2021

High speed railway system is progressed to SRN(Smart Railway Network) having entirely automation function beyond each componet automations. It is necessity to use mobile communication technology of LTE-R(Long Term Evolution - Railway) and 5G-R(5th Generation - Railway) and information technology of convergence based on AI, Big Data, Deep Learning to construct this smart railway networks. In this paper, a communication structure is suggested for SRN. This suggested communication structure for SRN is composed to include safety operation of high speed train, railway system management and customer services, and also have complexing function of these each functions. Results of this study can be used for SRN construction and opeation, and development of railway communication standards.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.1-8
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• 2020

The Ministry of Land, Infrastructure and Transport of Korea has been trying to spread integrated railway communication network technologies based on a major railway policy since 2012. As a result, the world's first commercial Long-Term Evolution - Railway (LTE-R) network was established on the Gangneung line (Manjong station - Gangneung station) and has been commercially operating as a railway communication system since 2017. Special function and performance requirements are needed for safe and efficient railway operations, such as group calls, emergency calls, functional addressing, and train control based on wireless communications. In this paper, we present functional and performance railway communications requirements that are based on European wireless railway communications systems. In addition, we measured communications characteristics and performance using a KTX field test on the Gangneung line to analyze the validity and reliability of the LTE-R network. Although the average Radio Frequency (RF) conditions were satisfied in the requirements, we found sudden communications quality degradation, such as Radio Link Failure (RLF) in some railway sections. We propose a way to improve performance and network installations based on in-depth analysis of LTE-R communications field-test results.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.9
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• pp.2073-2085
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• 2012

Recently, the International Telecommunication Union allocated the 470-862 MHz band to the digital broadcasting (DB) service. Moreover, the 790-862 MHz sub-band will be allocated to the next-generation mobile system, known as the International Mobile Telecommunication - Advanced (IMT-A), and to the DB on a co-primary basis in the year 2015. Currently, two candidate technologies are available to represent the IMT-A system; the Mobile WiMAX and Long Term Evolution - Advanced (LTE-A). One of the main criteria of the IMT-A candidate is to not cause additional interference to the primary service (i.e., DB). In this paper, we address the spectrum sharing issue between the IMT-A candidates and the DB service. More precisely, we investigate the interference effect between the DB service and the mobile network, which could be either LTE-A or WiMAX. Our study proposes a spectrum sharing model to take into account the impact of interference and evaluates the spectrum sharing requirements such as frequency separation and separation distance. This model considers three spectrum sharing scenarios: co-channel, zero guard band, and adjacent channel. A statistical analysis is performed, by considering the interferer spectrum emission mask and victim receiver blocking techniques. The interference-to-noise ratio is used as an essential spectrum sharing criterion between the systems. The model considers the random distribution of the users, antenna heights, and the bandwidth effect as well as the deployment environment in order to achieve spectrum sharing. The results show that LTE-A is preferable to WiMAX in terms of having less interference impact on DB; this can eventually allow the operation of both services without performance degradation and thus will lead to efficient utilization of the radio spectrum.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.7
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• pp.805-814
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• 2012

Intermittent or periodic signals with undulating amplitudes of mobile devices cause interference noise at audible frequency to the sound system which is installed nearby. In this regard, it is recently issued that the intermittently transmissions of LTE mobile phones cause the interference noises with sound systems, similar to that of GSM mobile phones. For retaining the immunity to noises, a national regulation KN20 suggests a 1 kHz AM 80 % and a CDMA modulation signal as reference signals for immunity test of sound and television broadcast receiver. In this paper, the effects of interference noises of AM and CDMA are compared with those of GSM and LTE, and the improvement of reference signal for national immunity test of sound systems is suggested. It is recommended to delete the CDMA modulation signal from reference signals for immunity test because it hardly cause interference noise with sound systems. On the other hand, it is desirable to select the modulation signal of LTE instead of CDMA as a reference signal for immunity test of sound system and television broadcast receiver because many people use the LTE service and it is analysed that the LTE signal causes considerable interference noises.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5C
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• pp.527-539
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• 2009

In this paper, we propose an asynchonous ICI (Inter-Cell Interference) mitigation techniques for 3GPP LTE MIMO-OFDMA down-link receiver. An increasing in symbol timing misalignments may occur relative to sychronous network as the result of BS (Base Station) timing differences. Such symbol synchronization errors that exceed the guard interval or the cyclic prefix duration may result in MAI (Multiple Access Interference) for other carriers. In particular, at the cell boundary, this MAI becomes a critical factor, leading to degraded channel throughput and severe asynchronous ICI. Hence, many researchers have investigated the interference mitigation method in the presence of asynchronous ICI and it appears that the knowledge of the SCM (Spatial Covariance Matrix) of the asynchronous ICI plus background noise is an important issue. Generally, it is assumed that the SCM estimated by using training symbols. However, it is difficult to measure the interference statistics for a long time and training symbol is also not appropriate for MIMO-OFDMA system such as LTE. Therefore, a noise reduction method is required to improve the estimation accuracy. Although the conventional time-domain low-pass type weighting method can be effective for noise reduction, it causes significant estimation error due to the spectral leakage in practical OFDM system. Therefore, we propose a time-domain sinc type weighing method which can not only reduce the noise effectively minimizing estimation error caused by the spectral leakage but also implement frequency-domain moving average filter easily. By using computer simulation, we show that the proposed method can provide up to 3dB SIR gain compared with the conventional method.

• IEIE Transactions on Smart Processing and Computing
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• v.2 no.6
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• pp.350-356
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• 2013

Single Carrier Frequency Domain Multiple Access (SC-FDMA) has proven to be the best long term evolution for uplink multiple access because of its low Peak to Average Power Ratio (PAPR), a feature that leads to low power consumption. This is achievable only if the resource allocation is performed in a contiguous manner. This paper proposes a new approach with an improvement in the global resources allocation. The new approach presented utilizes the gain function, which adopts some of the procedures deduced from the older Recursive Maximum Expansion (RME) algorithm. The experiment proved that the new approach is better than the original RME algorithms and in most cases, is closer to the optimal solution.

• Journal of Communications and Networks
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• v.17 no.1
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• pp.27-33
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• 2015

In this paper, we consider a joint frequency-domain scheduling and user-pairing problem for virtual MIMO in the single carrier frequency division multiple access (SC-FDMA) system, e.g., the uplink transmission for third generation partnership project-long term evolution (3GPP-LTE) standard. Due to the subcarrier adjacency constraint inherent to SC-FDMA, its complexity becomes unmanageable. We propose a greedy heuristic algorithm for PF scheduling so as to deal with the complexity issue in this joint problem. It has been shown that its performance can reach up to 90% of its upper bound.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.07a
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• pp.417-419
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• 2010

SC-FDMA(Single Carrier Frequency Division Multiple Access) 방식은 다중경로의 영향을 제거할 수 있는 OFDM(Orthogonal Frequency Division Multiplexing) 방식의 장점을 유지하면서 OFDM의 단점인 높은 PAPR(Peak to Average Power Ratio) 문제를 해결할 수 있어 차세대 멀티미디어용 이동통신 시스템인 3GPP LTE(3rd Generation Partnership Project Long Term Evolution)의 상향링크 전송방식으로 채택되었다. 또한 SC-FDMA 수신기는 주파수 영역에서 채널등화기를 구현함으로써 OFDM 수신기와 마찬가지로 기존의 단일반송파 방식에 비해 등화기의 복잡도를 크게 감소시킬 수 있다. 한편 주파수 영역 채널등화기와 더불어 시간영역의 판정궤환 등화기를 같이 사용하여 수신기의 성능을 향상 시킬수 있다. 이 논문에서는 예측형 판정궤환 등화기 구조를 적용하여 채널등화기의 성능을 더 향상시킬 수 있는 방법을 제안하고자 한다. 또 모의실험을 통해 제안된 방법의 성능을 확인한다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.06a
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• pp.204-205
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• 2013

최근 일본의 지진 쓰나미 등 전 세계적으로 많은 재난이 증가하고 있고, 국내에서는 신속한 재난 정보 전송을 위해서 CBS(Cell Broadcast Service) Alert Message를 국가 표준으로 제정하였다. CBS를 통한 전송은 지역단위 전송이 가능하므로 재난이 발생한 지역에 신속한 전송 서비스를 가능하게 해준다. 하지만 국내의 경우 CBS Alert Message가 LTE(Long Term Evolution) 단말에서만 수신이 가능하고 3G 단말에서는 수신이 불가능하다. 이에 본 논문은 실내 환경에서 gateway-AP(Access Point)를 이용하여 3G 단말이 CBS Alert Message를 수신 할 수 있는 방법을 제시하려고 한다.