【摘要】：Turbo碼是一種具有接近香農(nóng)理論極限優(yōu)異性能的信道編碼。它在信道編碼理論的發(fā)展歷程上具有里程碑式的意義,引起了學(xué)術(shù)界廣泛的關(guān)注與研究,并被廣泛應(yīng)用于第三代移動通信、衛(wèi)星通信、深空通信、數(shù)字音頻廣播(DAB)等領(lǐng)域。在高速率的無線信道中,多徑效應(yīng)會引起頻率的選擇性衰落,導(dǎo)致OFDM符號上的部分子載波數(shù)據(jù)丟失。而前向糾錯編碼是解決此問題的有效手段,通過子載波之間的糾錯編碼,在接收端,錯誤子載波可以通過其它無錯子載波之間的編碼相關(guān)性而得到恢復(fù)。將Turbo碼引入到OFDM系統(tǒng)中,可以極大地提高通信系統(tǒng)對抗突發(fā)干擾和頻率選擇性衰落的能力,而高效數(shù)字調(diào)制技術(shù)的引入又能進一步的提高系統(tǒng)頻譜利用率。因此本文研究了如何實現(xiàn)Turbo碼與高效數(shù)字調(diào)制技術(shù)以及OFDM調(diào)制技術(shù)的有效結(jié)合。本文首先分析了Turbo碼的基本原理和典型的Turbo譯碼算法,并在此理論基礎(chǔ)上,利用計算機對Turbo碼的性能進行了仿真,研究了交織長度、迭代譯碼次數(shù)以及編碼碼率的不同對誤碼性能的影響,結(jié)果表明,隨著交織長度的增加、迭代譯碼次數(shù)的增加以及編碼碼率的降低,誤碼性能都會相應(yīng)的提升,但同時也會提高其編譯碼的復(fù)雜度。其次設(shè)計了Turbo碼與高效調(diào)制技術(shù)相結(jié)合的傳輸系統(tǒng)方案,同樣也利用計算機對系統(tǒng)的誤碼性能進行了仿真分析。接下來著手設(shè)計了Turbo碼與高效調(diào)制技術(shù)以及OFDM技術(shù)相結(jié)合的綜合傳輸系統(tǒng),利用計算機對Turbo編碼前后系統(tǒng)的誤碼性能進行了對比仿真,結(jié)果表明,Turbo碼的引入能極大的提高OFDM傳輸系統(tǒng)的誤碼性能。最后對Turbo碼在LTE衛(wèi)星通信系統(tǒng)中的應(yīng)用進行了研究,為系統(tǒng)設(shè)計了1/3、1/2和3/4三種編碼碼率,以及QPSK、16QAM、64QAM、16APSK和32APSK五種調(diào)制方式以供選擇,并設(shè)置仿真參數(shù),利用計算機對系統(tǒng)編碼前后的誤碼性能進行了仿真,仿真結(jié)果表明,在相同條件下,引入了Turbo信道編碼之后,LTE物理衛(wèi)星傳輸系統(tǒng)的誤碼率急劇下降,系統(tǒng)誤碼性能得到極大改善,可靠性得到極大提升。本文設(shè)計的Turbo碼結(jié)合高效調(diào)制技術(shù)以及OFDM技術(shù)的傳輸方案,只是利用計算機軟件對系統(tǒng)誤碼性能進行了仿真分析,但并沒有著手搭建硬件平臺上具體實現(xiàn)該方案并研究其性能,這都有待于進一步實施。
[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.
【學(xué)位授予單位】：西安電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TN911.22

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本文編號：2256310