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摘要：对提高列车运行速度、保证行车安全来说是至关重要的车一地信息传输方式主要包括轨道电路、轨道环线、漏泄电缆、查询应答器、无线通信等。 在我国，目前以轨道电路方式为主。由于受到轨道电路带宽限制，采用传统数字调制方式的基于轨道电路的信息传输方式不能向列车运行控制系统车载设备提供大容量的信息，无法满足列车运行控制系统的需要。
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本毕业论文针对轨道电路频带窄的特点，提出了以正交频分复用 (OFDM)作为轨道电路的调制解调方式。通过使用MATLAB仿真软件对OFDM进行调制仿真，突出对于采用了OFDM调制解调技术的轨道载波通信系统，抗衰落能力强、误码率随着信噪比的增加而降低，所以数据流可以降低误码、安全、可靠地在轨道线上传输。由于OFDM调制技术对信道中信号帧加上循环前缀，并在传输过程中进行交织与前向纠错等技术处理，这样接收端就可以在一部分数据流因为干扰而发生错误，甚至是丢失的情况想，将接收到的信号复原。这样大大的提高了信号的抗干扰能力。
关键词: 轨道电路 ；信息传输 ；OFDM(正交频分复用)；调制解调9674
Track circuit based on OFDM modulation method
ABSTRACT： To improve train speed, to ensure traffic safety is essential car transmission of information in one place including track circuits, rail Link, leaky cable, query answering, wireless communications.
In China, currently the main way to track circuit. Because of track circuit bandwidth limitations, using the traditional digital modulation track circuit-based information transmission is not to train operation control system-board equipment to provide large-capacity information, unable to meet the needs of train operation control system.
In this paper, the characteristics of the track circuit narrow band,proposed orthogonal frequency pision multiplexing (OFDM) as a modulation and demodulation circuit track. By using MATLAB to make OFDM modulation simulation,to forcus the use of OFDM modulation and demodulation techniques track carrier communication system,Anti-fading ability is great , error rate decreases with the increase of SNR,so the data stream can reduce the error, safely and reliably transport the rail line.Because OFDM modulation with the cyclic prefix channel signal frame, and in the transmission process interleaving the forward error correction processing technology,so that the receiver can be a part of the data stream in the error occurs because of interference or even the loss of the case, the received signal restoration. This greatly improves the signal to noise immunity.
Keyword: track circuit, information transmission, OFDM, modulation and demodulation
目录
1 绪论6
1.1 前言…6
1.2 国内外轨道电路现状6
1.2.1 国内既有轨道电路…6
1.2.2 国外高速线采用的轨道电路…7
1.3 课题的目的和意义…8
1.4 国内外研究现状与水平…8
1.5 发展趋势…9
1.6 本章小结…9
2 轨道电路中的各种信号调制方法 …10
2.1 二进制幅移键控（2ASK）调制…10
2.2 二进制频移键控（2FSK）调制…11
2.3 二进制相移键控（2PSK）调制…12
2.4 最小频移键控（MSK）调制13
2.5 正交频分复用(OFDM)调制…13
2.6几种调制方式的比较13
2.7 本章小结14
3 OFDM调制 15
3.1 OFDM调制的特点15
3.2 OFDM的基本原理15
3.3 OFDM技术的优缺点…17
3.3.1 OFDM技术主要优点17
3.3.2 OFDM技术的不足之处…17
3.4 OFDM技术的发展 …18
3.5 OFDM技术的应用现状与前景 …18