High Quality Data Service On The Train

Published Date: 02 Nov 2017

Nowadays, the data demand for the mobile network is increasing. More and more people use the mobile terminal (smartphone, IPad, laptop, etc.) to do anything everywhere, especially on the public traffic like coach or the train. Meanwhile, the development of high speed railway is very quickly all over the world. The maximum speed is about 300km/h for lots of railway systems in the UK, Germany, France, China and Japan, etc (International Union of Railways, 2009). In Shanghai, a city in of China, the maglev train’s speed is 431km/h (Railway Gazette International, 2012) and the world speed has reached to 581km/h (Japanese experimental MLX01) (The Japan Times Online, 2011). The high speed will result to a bad environment of communication. The signal can be affected by the Doppler Effect and Multipath effect.

The first system which is used in the first train is signal flag system on 1825 in UK. Then, the lights were used in the system. On the year of 1839, the British railway began to use telegram and Closed-circuit signal system was operated in USA in 1923 (Dr James B. Calvert, 2012). With the development of communication and computer science, the signal and system in railway has become intelligent and wireless. GSM-R is a part of European Rail Traffic Management System (ERTMS) and it is designed for the railway particularly in order to adapt to the high-speed environment. Now, GSM-R is operating in the 38 countries all over the world and it has been an international standard for wireless communication in railway applications. In the United Kingdom, over 14000 km GSM-R railway is planned (European Railways Implementation Group, 2007).

1.2 literature review

GSM-R can provide services like communication among train diver, control centre and train stations, voice call, railway emergency call, etc (Kastell et al.,2006).

In GSM-R, GMSK (Gaussian Filtered Minimum Shift Keying) is used as a modulation technology. Although the performance is good, the disadvantage about it is that the bandwidth efficiency is low although it has a good bit error performance. Because in the limited spectrum resource time, low bandwidth efficiency could be diseconomy. Moreover, the convolutional code is used in the system as the method of channel coding. The coding and decoding way are a complex which will result to the large transmission delay.

According to Hofestadt (1995), GSM-R is specified for speed up to 250km/h and a trackside signal to noise ratio is 10dB for the link performance up to 500km/h. Actually, GSM-R is the Second Generation Telecommunication technology. And it cannot provide high volume data service which means that GMS-R will not provide good quality internet service for the passenger. However, the 3G (Third Generation Telecommunication) or the 4G (fourth Generation Telecommunication) can do it. Generally speaking, in the moving environment, the 3G will provide at least144kbps and up to 2Mbps data rate (Prasad, 1998) and 4G will have data rate from 1Gbps to 100Mbps (Ivanek, Ferdo, 2007) but the 2G will only provide data rates only from 9.6kbps up to 14.4kbps (Hillebrand, Friedhelm, 2001). Because of modern access technology, the quality and capacity of communication has been improved greatly.

In the high speed mobile environment, two serious problem will have influence to the communication which are Doppler Effect and Multipath Effect. High velocity result to the Doppler Effect and this effect will make the frequency shift. According to Matthias Pätzold (2002), assuming the train’s velocity is 400km/h, the carrier frequency is 900MHz which is the standard of 3G, and then the maximum shift is

This high frequency shift will increase the error rate because the receiver cannot pick up the right frequency of signal.

Because of the building in the urban or the hill in the rural, the signal may get to the receiver through reflecting or refracting, Multipath Effect occurs. Then the signal will not get to the receiver at the same time which can increase the difficulty for signal detection (Matthias Pätzold, 2002).

In LTE which is one of the fourth generation technology, lots of new methods are used. For example, the OFDM (Orthogonal Frequency Division Multiplexing) technique, the MIMO (Multiple Input Multiple Output) antenna technique. These techniques can decrease the affect for the Doppler Effect and Multipath Effect. Now, LTE can accept the terminal using the high quality network services in the speed of 500km/h (Dahlman et al. 2011).

Therefore, in order to enhance the speed and quality of data transmission and ensure the reliability and stability for the data, it is necessary to do some research about the communication system in the high-speed mobile environment.

Afterwards, when conducting the research, more specific articles about communication channel, the code and modulation methods and communication in the railway are necessary to be found and read.

2. Problem definition, questions, hypotheses and aims for the research

2.1 Aims and planned outcomes from the research

The final aim about this research is to design a better railway wireless communication system than the GSM-R which can provide high quality data service. In order to achieve the goal, some aims need to be done:

(1) To understand the characteristics of railway communication channel.

(2) Choose some adaptive techniques which can be used in the different part of the communication system.

(3) Design a good application system for passengers and administrators

2.2 Problem definition, research questions and hypotheses

The top level research problem is that how to improve the communication system in order to provide high quality network service.

The basic signal transmission is made up by coding, modulating and transmitting. So the top research problem can be divided into three sub-questions obviously. The first is that how to choose a good code method. The second is to choose a good modulation method which can adapt to the channel and designing a good antenna system is the third problem.

In the LTE standard, OFDM technique and MIMO technique are used. OFDM technique can enhanced the bandwidth efficiency and reduce the interference of noise (Dahlman et al. 2011). MIMO antenna system uses groups of antenna transceiver to reduce the signal ambiguity which multipath effect brings.

Concerning the channel coding, LDPC (Low Density Parity Check) code was found in 1952 by R. Gallager in 1963 but it was ignored. But its rediscovery is the most important achievement in the coding theory area these 10 years. Now it has been the best code as it can approach the Shannon limit mostly. Moreover, the complexity of coding and decoding is not very high and it can be parallel decoded which will boost the process of transmission.

Therefore, some hypotheses can be put forward. Firstly, OFDM can enhance the efficiency of transmission and provide the high bit rate. Secondly, MIMO system adapts to the environment for the train goes through (urban area, rural area, etc.) and has good quality in resisting the Doppler Effect. Lastly, LDPC code can make a take a good performance in the channel.

3. Research philosophy and paradigm

Two paradigms or philosophies will be used in this research which are positivism and phenomenology.

When analysing the current system, phenomenological research method will be used. The interview about the service and experience on the train to passengers and the train driver or the railway administrator is necessary. Then, the interview data should be formally analysed and it is useful for helping formulate the system parameter and structure, e.g., the system level model, the data rate, the requirement of data delay time.

Meanwhile, when choosing specific schemes, this method also useful for deciding. The interview can be done among the scientists, the engineers or the Internet Service Provider. By thinking of their opinions about the project, it is benefit for conductor to understand the whole project.

Positivism method is needed as well. This research is about the engineering, so more experiment can be done. After finishing hypothesis, we can verify it by the experiment and mathematical calculation. For example, in order to verify the hypothesis that LDPC code has a good performance in the railway communication system, some steps below need to be done. First, from the literature review, we should get a good understanding about it. Then, we can choose some ways about coding and decoding and compare their performance. After that, we need to do the simulation and practical test. The simulation should start at the basic channel model in order to simply the simulation first. After that, we can change the channel model to the model using now to consider the adaptability. On one hand, if the effect is not good, some schemes need to be considered and on the other hand, if the effect is good, some modulation methods also need to be tested to improve the LDPC codes’ effect. After simulation, the hardware emulation and actual communication platform need to be built to test the real performance. And the process of the experiment may repeat to reach the requirement.

4. Plan and selection of techniques for acquiring and analysing information and data

4.1 selection of techniques

4.1.1 Selection of coding methods

LDPC (Low Density Parity Check) code was found in 1952 by R. Gallager in 1962 but it was ignored. Its rediscovery is the most important achievement in the coding theory area these 10 years. Now it has been the code which can approach the Shannon limit mostly. The complexity of coding and decoding is not very high. QC (Quasi-Cyclic) –LDPC is a kind of LDPC which is designed elaborately and it has lots of benefits for high quality communication system and storage system. For example, it is easy for coding, and the degree of parallelism, convergence is excellent. Now QC-LPDC has been the standard for IEEE 802.16e (IEEE, 2008). So, it is very necessary to find a good coding and decoding method and discuss the performance about it in high-speed mobile channel.

4.1.2 Selection of modulation technology

According to Shen et al. (2006), OFDM (Orthogonal frequency-division multiplexing) is a new modulation technology which can divide the whole channel to some small channel. The bandwidth efficiency is very high and different small channels are Orthogonal. In mobile communication system, two problems need to be considered which are Multipath Effect and Doppler Effect. However, OFDM cannot performance well to reduce Doppler Effect. So, something must be considered to improve the OFDM and enhance the capacity reducing the Doppler Effect.

4.1.3 Selection of antenna system

MIMO system has been widely adopted in the fourth-generation mobile communication technology, for example, Wi-max, LTE, etc. This system allows the antenna distinguish signal sent or from the different spatial orientation and those signal will be analysed so that it can effectively overcome signal fading, and reduce the error rate. If considering different parts of the environment the train goes through, and well-designed MIMO system the impact of adverse factors in mobile communications can be reduced (Shen et al., 2006).

4.2 techniques for acquiring and analysing information and data

As this research is an engineering project, different step needs different techniques for acquisition.

At the stage of conceptual design and parameters definition, we design questionnaire and interview ordinary users, managers and engineers to obtain the primary qualitative data. After classifying data, we make the list respectively to discuss the needs about basis of technical and specific application. It will be better to evaluate the entire system and to well understand research and the target.

In the literature search stage, we search the relevant literature, obtain secondary data to get better understand about the choices and conclusions in the previous research, views and choice of technologies on issues. After collecting quantitative and qualitative data, analysis, comparison and discussion related to our own research are very important.

We use Matlab to do the experiments and data analysis. Evaluating the communication system usually consists of evaluate the bit error rate, transmission delay, and the data transmission rate. In the simulation experiments, we will get quantitative data and in order to compare performance between GSM-R model and our design models, we should draw the BER under different conditions, the transmission delay and transmission rate by using the line chart and do study about the chart to judge whether the quality has improved.

In the actual test, we need to design special software to get the performance parameters of the communication system and do the comparison between it and the simulation data by using the same method in the experiment stage to verify the consistency about the experiment and actual test.

5. Outline content of final report and nature of conclusions and outcomes

The final report will have three parts. Every part also has some sections.

Aims and planned outcomes

Why we need this research

What will this research will give us

Testing and validation

Conclusion and looking forward to the future

Final report

Research Introduction

Application level

Basic level

The whole platform diagram

Techniques will be used

Coding techniques

Modulation techniques

Antenna system design

Laboratory simulation

Operational test

Performance analysis