Hongli Zhao

Design and performance tests in an integrated TD-LTE based train ground communication system

In existing urban rail transit systems, the train ground communication system for different applications are deployed independently. Investing and constructing the communication infrastructures repeatedly not only wastes substantial social resources, it also brings difficulties to maintain all these infrastructures. In this paper, we first present the communication Quality of Service (QoS) requirement for different train ground applications. An integrated TD-LTE based train ground communication system for the urban rail transit system is designed next, which includes all the applications in urban rail transit system. In order to test the integrated TD-LTE based train ground communication system performance, an indoor testing environment is set up. The channel simulator and programmable attenuators are used to simulate the real urban rail transit environment. Extensive test results show that the designed integrated TD-LTE based train ground communication system performance satisfies urban rail transit communication requirement.

A novel handoff decision algorithm in TD-LTE based train-ground communication system

Communication Based Train Control (CBTC) system is a kind of advanced train automatic control system that integrates radio communication and automation control technology. Handoff happens frequently in CBTC train ground communication system, which may result in communication interrupt and long latency. In this paper, we propose a new handoff decision algorithm based on improved Grey Verhulst model for the Time Division-Long Term Evolution (TD-LTE) based train-ground communication system. The proposed handoff decision algorithm can be used under free space and leaky coaxial cable equipped environment. Improved Grey Verhulst model is used to predict the Reference Signal Receiving Power (RSRP) values from two Radio Remote Units (RRU). Compared with traditional Verhulst model, improved Grey Verhulst model can optimize parameters to eliminate the inherent errors in data sequence prediction. The handoff decision action is performed based on the predicted RSRP values. Simulation results show that the proposed handoff decision algorithm can decrease ping-pong handoff and improve the handoff delay compared with the traditional A3 event based scheme in LTE systems.

QoS-Aware Resource Allocation for Network Virtualization in an Integrated Train Ground Communication System

Urban rail transit plays an increasingly important role in urbanization processes. Communications-Based Train Control (CBTC) Systems, Passenger Information Systems (PIS), and Closed Circuit Television (CCTV) are key applications of urban rail transit to ensure its normal operation. In existing urban rail transit systems, different applications are deployed with independent train ground communication systems. When the train ground communication systems are built repeatedly, limited wireless spectrum will be wasted, and the maintenance work will also become complicated. In this paper, we design a network virtualization based integrated train ground communication system, in which all the applications in urban rail transit can share the same physical infrastructure. In order to better satisfy the Quality of Service (QoS) requirement of each application, this paper proposes a virtual resource allocation algorithm based on QoS guarantee, base station load balance, and application station fairness. Moreover, with the latest achievement of distributed convex optimization, we exploit a novel distributed optimization method based on alternating direction method of multipliers (ADMM) to solve the virtual resource allocation problem. Extensive simulation results indicate that the QoS of the designed integrated train ground communication system can be improved significantly using the proposed algorithm.

The QoS Indicators Analysis of Integrated EUHT Wireless Communication System Based on Urban Rail Transit in High-Speed Scenario

Nowadays, in urban rail transit systems, train wayside communication system uses Wireless Local Area Network (WLAN) as wireless technologies to achieve safety-related information exchange between trains and wayside equipment. However, according to the high speed mobility of trains and the limitations of frequency band, WLAN is unable to meet the demands of future intracity and intercity rail transit. And although the Time Division-Long Term Evolution (TD-LTE) technology has high performance compared with WLAN, only 20 MHz bandwidth can be used at most. Moreover, in high-speed scenario over 300 km/h, TD-LTE can hardly meet the future requirement as well. The equipment based on Enhanced Ultra High Throughput (EUHT) technology can achieve a better performance in high-speed scenario compared with WLAN and TD-LTE. Furthermore, it allows using the frequency resource flexibly based on 5.8 GHz, such as 20 MHz, 40 MHz, and 80 MHz. In this paper, we set up an EUHT wireless communication system for urban rail transit in high-speed scenario integrated all the traffics of it. An outdoor testing environment in Beijing-Tianjin High-speed Railway is set up to measure the performance of integrated EUHT wireless communication system based on urban rail transit. The communication delay, handoff latency, and throughput of this system are analyzed. Extensive testing results show that the Quality of Service (QoS) of the designed integrated EUHT wireless communication system satisfies the requirements of urban rail transit system in high-speed scenario. Moreover, compared with testing results of TD-LTE which we got before, the maximum handoff latency of safety-critical traffics can be decreased from 225 ms to 150 ms. The performance of throughput-critical traffics can achieve 2-way 2 Mbps CCTV and 1-way 8 Mbps PIS which are much better than 2-way 1 Mbps CCTV and 1-way 2 Mbps PIS in TD-LTE.

Virtual resource allocation in a network virtualization based integrated train ground communication system

Train ground communication systems for different applications are deployed and managed independently in current urban rail transit systems with Wireless Local Area Network (WLAN) technology. Investing and constructing communication infrastructures repeatedly not only waste substantial social resources but also bring many difficulties to maintain all these infrastructures. In this paper, we design a network virtualization based integrated train ground communication system for urban rail transit systems. The virtual resource allocation in the integrated system is formulated as an optimization problem. On the premise that the train ground communication requirement of communication based train control system is guaranteed, the optimization objective is to maximize the long-term general utility for all the urban rail transit applications. We use the distributed method based on alternating direction method of multipliers (ADMM) to solve the optimization problem. Simulation results show that the designed integrated train ground communication system quality of service (QoS) can be improved effectively with the proposed approach.

Field test results analysis in urban rail transit train ground communication systems of integrated service using LTE-M

Different services are separated by independent train ground communication networks in existing urban rail transit systems. Most of the independent train ground communication system are using IEEE 802.11 based WLAN technologies, which has many drawbacks when used in urban rail transit system, such as high speed performance degradation, open free frequency, etc. In this paper, we design a train ground communication system for Integrated Service in urban rail transit/metro system using LTE technology (LTE-M). Dedicated frequency spectrum is used in the LTE-M based system. The real LTE-M based system is built on the ring rail line in Beijing to perform the field test. The performance of the integrated services including the CBTC, PIS, IMS and TOSM (Train Operation State Monitoring) are tested. Extensive test results show the advantages of LTE-M. The test results analysis also illustrates the disadvantages of using LTE-M in urban rail, and gives some advises for LTE-M based system design in engineering.

The QoS analysis of train-ground communication system based on TD-LTE in urban rail transit

Wireless Local Area Network (WLAN) is currently used in the train-ground communication for the urban rail transit systems. Due to the high speed and frequency band limitations, WLAN is unable to meet the demand of future city and intercity rail transit. Time Division-Long Term Evolution (TD-LTE) technology allows to construct a flexible service environment compared with current WLAN based system. In this paper, a TD-LTE based train-ground communication system for the urban rail transit system is given. It integrates all the applications in urban rail transit system. An outdoor testing environment is set up to test the performance of the integrated TD-LTE based train-ground communication system. The packet loss rate, response time, throughput of the TD-LTE system are analyzed. Extensive testing results show that the Quality of Service (QoS) of the integrated TD-LTE based train-ground communication system satisfies the requirements of urban rail transit system.