Hanbyeog Cho

Challenges of LTE high-speed railway network to coexist with LTE public safety network

As the speed of train trialled by the French National Rail Corporation has reached more than 500 km/h, the secure and continuous connection to the train control system has only grown more important. In this paper, current status and progress of national disaster safety network project and LTE-based integrated wireless network for railway in Korea, firstly, and the major challenges of LTE-R network to coexist with LTE public safety network are addressed in the aspect of the air interface requirements for the essential railway services. In our view, it is the most important thing at present for designing and planning LTE railway network to eliminate - not to mitigate or reduce - the radio interference, especially from the adjacent LTE public safety network to LTE-based wireless train control because they use the same frequency band.

A Study on Integration Scheme of Wireless Communications in Railway Wireless Network

The current railway wireless network uses various communication scheme depending on the section of railway. Therefore, in the train, it is required a specific communication device for the corresponding communication scheme to communicate and exchange data with the control center. To enhance data rate and support various services, LTE-R scheme has been developed for the next generation railway communications. To use both the existing communication and LTE-R schemes, it is required an integration method for encompassing all communication schemes. In this paper, we overview existing railway communications and LTE-R scheme. Then, we develop a network integration method which can be applied by using one terminal in the train. In addition, implementation issues for the integration are also considered.

Performance of Relay Networks with Partially Differential Modulation Scheme Depending on Energy Allocation in Railway Environments

In relay networks, relay nodes amplify or demodulate/remodulate the received signal from the transmitter, and transmit that signal to the receiver. The received signals from several relays are combined and used for demodulation at the receiver, which enhances the performance of the overall system. Partially differential modulation scheme which uses coherent modulation at the relay and non-coherent modulation scheme at the receiver is adopted for modulation scheme. We analyze the performance of systems depending on various energy allocations of source and relays given the total energy in relay networks.

Effect of Relay Location in Cooperative Networks with Partially Differential Modulation Scheme

Cooperative networks eliminate shadow area using relay and enhance communication performance by creating virtual multi input multi output (MIMO) system. In this paper, we analyze the performance of cooperative networks which use coherent modulation scheme in source-relay nodes and differential modulation scheme in relay-destination nodes depending on the relay location. We consider the performance analysis of systems with and without the direct transmission between source and destination node where the direct transmission adopts differential modulation scheme. In addition, the performance of the system with fully differential modulation scheme is compared with the system using partially differential modulation scheme. The performance of system is based on the symbol error rate between source and destination node. 키워드 Cooperative Networks, Relay Networks, Relay Location, Performance, Error Rate 협력네트워크, 중계네트워크, 중계기위치, 성능, 오류율 * 중원대학교 컴퓨터시스템공학과 (wcho@jwu.ac.kr) ** 교신저자 (corresponding author) : 한국전자통신연구원 (hbcho@etri.re.kr) 접수일자 : 2015. 06. 16 심사(수정)일자 : 2015. 06. 13 게재확정일자 : 2015. 06. 23 I. 서 론 협력네트워크는 송신기와 수신기간에 데이터 송수 신시 중계기를 이용하여 신호를 전송함으로써 가상의 안테나 배열을 형성할 수 있다. 이러한 가상의 안테나 배열은 각 중계기가 하나의 안테나를 이용하더라도 다중 입출력 시스템을 형성함으로써 전체시스템의 성 능을 향상시킬 수 있다[1-3]. 협력네트워크의 대표적 http://dx.doi.org/10.13067/JKIECS.2015.10.6.671 JKIECS, vol. 10, no. 6, 671-676, 2015 672 인 프로토콜을 중계기의 역할에 따라 두 가지로 나누 어지는데, 중계기가 송신기로부터 수신된 신호를 단순 히 증폭해서 수신기로 전송해주는 증폭 후 전송 (AF: Amplify-and-Forward)방식과 중계기가 송신기로부터 수신된 신호를 복조 및 재변조 하여 수신기로 신호를 전송해주는 복조 후 전송 (DF: Decode-and-Forward) 방식이 있다. 신호의 전송은 송신기, 중계기 및 수신 기 사이에 전송되는 신호의 변복조 방식에 따라 동기 (coherent)방식과 비동기(noncoherent)방식으로 나눌 수 있다. 동기방식은 각 노드들 사이에서 채널정보를 이용하는 방식이며, 비동기방식은 채널정보를 이용하 지 않고 신호를 복조하는 방식이다. 비동기방식중 대 표적인 방식이 차등변조 방식인데, 차등변조 방식은 채널이 급격히 변하는 차량통신환경이나 기차통신환 경에 적용이 가능하다. 차량통신환경 에서의 다양한 이슈와 성능들이 소개되었으며[4-5], 차등변조 방식을 이용한 협력네트워크의 성능이 다양한 프로토콜을 적 용하여 분석되었다[6-7]. 본 논문에서는 부분차등변조 방식을 이용한 협력네트워크의 성능을 중계기의 위치 에 따라 분석하고 최적의 성능을 제공하는 중계기의 위치가 존재하는지 확인한다. 부분차등변조 방식을 이 용한 협력네트워크의 성능은 중계기의 위치에 따라 차이가 발생하는 것을 확인하였으나, 최적의 성능을 제공하는 중계기의 위치에 대한 분석은 이루어지지 않았다[8]. 본 논문에서는 송신기와 수신기 사이의 직 접파의 유무에 따라 중계기의 위치가 전체 시스템의 성능에 미치는 효과를 분석한다.

Trends of LTE based Railway Communication Systems

Since the KTX starts operation in 2004, Korean railway system has sustained the highest safety and accuracy. In order to keep this achievement, the LTE based wireless communication system has been introduced for mobile communications and signal transmission. railway, and activities for its standardization are on the way. Railway communication system will be used as part of national safety net through interworking with safety network. This paper reviews the contents of standards and technologies in an LTE-based railway communication(LTE-R) system, and the items to be standardized to improve operational efficiency of the railway system by building a national railway radio communication system.

Research on Design of LTE-Based High-Speed Railway Networks in Korea: Current and Emerging Issues

In this paper firstly current state and progress of LTE-based public safety network construction project is described, secondly emerging issues with designing LTE high-speed railway network are discussed, and finally a conclusion and future works are addressed. Two LTE networks are several similar features of LTE for public safety based radio access technology, 700 MHz frequency band, 10 MHz bandwidth, and nationwide deployment. Since the inter-network interference can cause the call disconnection with wireless train control which results in a fatal train accident, it is the most important thing at present for designing and planning LTE railway network to eliminate—not to mitigate or reduce—the radio interference, and therefore in our view it urgently needs to secure the reliability and survivability of the wireless train control system when we design and deploy both LTE networks together.

A survey on dual-band polar transmitter architecture for railroad wireless communication

In this study, we briefly introduce a novel concept of dual-band polar transmitter design based on digital quadrature modulation techniques for the application of railroad wireless communication (e.g., TRS & GSM-R) to reduce the bandwidth of dual-band PM (phase modulation) signal. We show that the complex signal processing at low frequency effectively utilizes the polar transmitter which is susceptible to the bandwidth of PM signal. Also, we evaluated the zero-crossing rate of two different schemes. There is the remarkable reduction of zero-crossing rate, compared to the conventional scheme.

Robust Digital Retrodirective Beamforming Technique for Multipath Channel Environment

Abstract In this paper, we describe the effect of temporal and spatial focusing obtained by using the digital retrodirective beamforming (DRDB) system and analyze BER performance of DRDB in multipath channel. There is a problem with reception performance degraded due to inter symbol interference (ISI) in multipath channel. In order to reduce ISI, the existing communication system use complex equalizer. In order to reduce ISI, we propose a DRDB system which can retransmit data information toward direction as the received signal without any prior information. Also, we explain ISI mitigation by temporal and spatial focusing of the proposed system. Simulation results show that the proposed system has better BER performance than that without DRDB becauseof ISI mitigation effect in multipath channel environment.

Smart Roadside Server for Driver Assistance and Safety Warning: Framework and Applications

In many countries, various in-vehicle Telematics systems are already available, while new systems are being currently designed. This paper introduces a smart roadside server for driver assistance and traffic safety warning. In recent world wide projects, roadside equipment is used for wider applications and becomes a server with more intelligent functions. This paper introduces a concept and framework of smart roadside server in various road systems using Telematics system. We suggest two service and application models in signalized intersection and SMART highway. This system models provide a vehicular safety service to a vehicle terminal of a vehicle located on a road within a service area from a smart roadside server. The smart roadside server is useful for driver assistance and warning by Telematics devices.

An OFDM System Design with Efficient ICI Cancellation over Embedded LTE-R Channels Based on the USRP Platform

In this paper, we design an OFDM communication system with ICI cancellation embedded over LTE-R channel. In our proposed system, a very fast time-varying multipath fading channel is integrated with the use of D2a scenario of WINNER II channel model. The ICI cancellation approaches, wherein a PSK modulated symbol is mapped onto multiple subcarriers, are investigated and deployed in the Universal Software Radio Peripheral platform as the RF front-end. Experimental results confirm that the ICI cancellation techniques offer a notably high performance on eliminating the problem caused by frequency offsets. For instance, the ICI cancellation solutions achieve the same performance at Doppler frequency of 200 Hz compared to the system without using our approaches at a lower Doppler of 50 Hz.