Turbo码在OFDM传输系统中的应用研究

发布时间：2018-10-08 09:43

【摘要】：Turbo码是一种具有接近香农理论极限优异性能的信道编码。它在信道编码理论的发展历程上具有里程碑式的意义,引起了学术界广泛的关注与研究,并被广泛应用于第三代移动通信、卫星通信、深空通信、数字音频广播(DAB)等领域。在高速率的无线信道中,多径效应会引起频率的选择性衰落,导致OFDM符号上的部分子载波数据丢失。而前向纠错编码是解决此问题的有效手段,通过子载波之间的纠错编码,在接收端,错误子载波可以通过其它无错子载波之间的编码相关性而得到恢复。将Turbo码引入到OFDM系统中,可以极大地提高通信系统对抗突发干扰和频率选择性衰落的能力,而高效数字调制技术的引入又能进一步的提高系统频谱利用率。因此本文研究了如何实现Turbo码与高效数字调制技术以及OFDM调制技术的有效结合。本文首先分析了Turbo码的基本原理和典型的Turbo译码算法,并在此理论基础上,利用计算机对Turbo码的性能进行了仿真,研究了交织长度、迭代译码次数以及编码码率的不同对误码性能的影响,结果表明,随着交织长度的增加、迭代译码次数的增加以及编码码率的降低,误码性能都会相应的提升,但同时也会提高其编译码的复杂度。其次设计了Turbo码与高效调制技术相结合的传输系统方案,同样也利用计算机对系统的误码性能进行了仿真分析。接下来着手设计了Turbo码与高效调制技术以及OFDM技术相结合的综合传输系统,利用计算机对Turbo编码前后系统的误码性能进行了对比仿真,结果表明,Turbo码的引入能极大的提高OFDM传输系统的误码性能。最后对Turbo码在LTE卫星通信系统中的应用进行了研究,为系统设计了1/3、1/2和3/4三种编码码率,以及QPSK、16QAM、64QAM、16APSK和32APSK五种调制方式以供选择,并设置仿真参数,利用计算机对系统编码前后的误码性能进行了仿真,仿真结果表明,在相同条件下,引入了Turbo信道编码之后,LTE物理卫星传输系统的误码率急剧下降,系统误码性能得到极大改善,可靠性得到极大提升。本文设计的Turbo码结合高效调制技术以及OFDM技术的传输方案,只是利用计算机软件对系统误码性能进行了仿真分析,但并没有着手搭建硬件平台上具体实现该方案并研究其性能,这都有待于进一步实施。
[Abstract]:Turbo code is a channel code with excellent performance close to Shannon's theoretical limit. It has a landmark significance in the development of channel coding theory and has attracted extensive attention and research in academic circles. It has been widely used in the third generation mobile communication, satellite communication, deep space communication, digital audio broadcast (DAB) and other fields. In high rate wireless channels, the multipath effect will cause frequency selective fading, resulting in the loss of partial subcarrier data on OFDM symbols. Forward error correction coding is an effective method to solve this problem. Error subcarriers can be recovered by coding correlation between other error-free subcarriers at the receiving end through the error correction coding between subcarriers. Introducing Turbo code into OFDM system can greatly improve the ability of communication system to resist burst interference and frequency selective fading, and the introduction of efficient digital modulation technology can further improve the spectral efficiency of the system. Therefore, this paper studies how to realize the effective combination of Turbo code and efficient digital modulation technology and OFDM modulation technology. In this paper, the basic principle of Turbo code and the typical Turbo decoding algorithm are analyzed. On the basis of this theory, the performance of Turbo code is simulated by computer, and the interleaving length is studied. The results show that with the increase of interleaving length, the increase of iterative decoding times and the decrease of coding rate, the error performance will be improved accordingly. But it also increases the complexity of encoding and decoding. Secondly, the transmission system scheme which combines Turbo code with high efficiency modulation technology is designed, and the error performance of the system is also simulated by computer. Then, the integrated transmission system combining Turbo code with high efficiency modulation technology and OFDM technology is designed, and the error performance of the system before and after Turbo coding is compared and simulated by computer. The results show that the introduction of turbo codes can greatly improve the error performance of OFDM transmission systems. Finally, the application of Turbo code in LTE satellite communication system is studied. Three coding rates of 1 / 3 / 1 / 2 and 3 / 4, and five modulation modes of QPSK,16QAM,64QAM,16APSK and 32APSK are designed for the system, and the simulation parameters are set up. The performance of the system before and after coding is simulated by computer. The simulation results show that, under the same conditions, the bit error rate of the physical satellite transmission system decreases sharply after the introduction of Turbo channel coding. The error performance and reliability of the system are greatly improved. The Turbo code combined with high efficiency modulation technology and the transmission scheme of OFDM technology are designed in this paper. The performance of the system is only simulated and analyzed by computer software, but the scheme is not implemented on the hardware platform and its performance is studied. This needs to be further implemented.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN911.22

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