本文關(guān)鍵詞： 自由空間光通信 低密度奇偶校驗碼 Gamma-Gamma分布 對數(shù)域BP算法 歸一化最小和算法　出處：《吉林大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：自由空間光(Free Space Optical,FSO)通信是一種新型的無線通信方式,作為最后一公里解決方案已經(jīng)成為近年來研究的熱點,它以激光作為載體把信息加載到激光上發(fā)送到大氣進(jìn)行傳輸。FSO通信具有廣泛的應(yīng)用領(lǐng)域。例如:深空通信、中軌道、地面之間的復(fù)雜地形導(dǎo)致的其它通信方式實現(xiàn)困難的通信,在一些特殊情況下還可以進(jìn)行地面與衛(wèi)星之間的通信,一般情況下把地面之間的激光通信稱為“大氣激光通信”。FSO通信系統(tǒng)之所以受到越來越多學(xué)者們的青睞,主要是因為這種通信技術(shù)具有如下優(yōu)勢:它具有相當(dāng)高的傳輸速率,不亞于光纖的傳輸速率,在一些特殊情況下,FSO通信的最高通信速率可達(dá)到56 Gb/s;FSO通信技術(shù)不受帶寬的限制,相對于射頻無線通信在頻譜資源上有著很大的優(yōu)勢。雖然FSO通信技術(shù)具有諸多優(yōu)勢,在其發(fā)展中也存在著技術(shù)瓶頸。在激光通信中,大氣的影響和光強(qiáng)起伏是限制通信質(zhì)量和通信距離的主要原因。為了抑制大氣對通信性能的不良作用,國內(nèi)外的學(xué)者們在不同方面進(jìn)行了研究,其中主要技術(shù)有:光源技術(shù)、自適應(yīng)校正技術(shù)、編碼與調(diào)制技術(shù)等,其中信道編譯碼是本文研究的重點。低密度奇偶校驗(Low Density Parity Check,LDPC)碼是具有逼近Shannon極限性能的好碼型,它具有極低的錯誤平層。由于性能優(yōu)異,使得LDPC碼在無線通信領(lǐng)域應(yīng)用廣泛,并成為第四代移動通信的標(biāo)準(zhǔn)之一。但是,對它在自由空間光通信領(lǐng)域中的應(yīng)用研究還具有很大的挖掘空間,本文正是以此為出發(fā)點展開的。本文首先介紹了大氣激光通信的相關(guān)理論知識。在介紹了幾種基本的信道模型后,詳細(xì)分析了大氣中各種噪聲,并給出了大氣信道模型。綜合各種大氣湍流信道噪聲對通信鏈路造成的干擾,采用了與實測數(shù)據(jù)較為一致的Gamma-Gamma分布作為信道模型。研究了LDPC碼的結(jié)構(gòu)和校驗矩陣的構(gòu)造方法和LDPC碼的幾種迭代譯碼算法,包括概率域BP算法、對數(shù)域BP(LLR BP)算法、最小和(Min Sum)算法、歸一化最小和算法、迭代APP算法等多種算法,提出了一種基于歸一化最小和算法的改進(jìn)算法,并在各種湍流強(qiáng)度信道下對各譯碼算法在復(fù)雜度和性能上進(jìn)行了比較和仿真分析。然后在Gamma-Gamma信道模型上對幾種譯碼算法進(jìn)行了仿真比較,分析所提出的改進(jìn)算法相比于最小和算法、LLR BP算法的性能提升。最后討論了迭代次數(shù)和碼長選取對譯碼性能的影響。
[Abstract]:Free Space Optical Space (FSO) communication is a new type of wireless communication. As a last kilometer solution, it has become a hot research topic in recent years. It takes the laser as the carrier to load the information into the laser and send it to the atmosphere for transmission. FSO communication has a wide range of applications. For example: deep space communication, intermediate orbit, complex terrain between the ground caused by other means of communication to achieve difficult communication, In some special cases, it is possible to communicate between the ground and the satellite. Generally speaking, the laser communication between the ground and the earth is called "atmospheric laser communication" .FSO communication system is favored by more and more scholars. The main reason is that this kind of communication technology has the following advantages: it has quite high transmission rate, no less than the transmission rate of optical fiber, and in some special cases the highest communication rate of FSO communication can reach 56Gb / s / FSO communication technology, which is not limited by bandwidth. Compared with RF wireless communication, it has a great advantage in spectrum resources. Although FSO communication technology has many advantages, there are also technical bottlenecks in its development. The influence of atmosphere and the fluctuation of light intensity are the main reasons for limiting the communication quality and communication distance. In order to restrain the adverse effect of atmosphere on the communication performance, scholars at home and abroad have carried out research in different aspects, among which the main technologies are: light source technology, Adaptive correction techniques, coding and modulation techniques, among which channel coding and decoding are the focus of this paper. Low density parity check low Density Parity check LDPCs are good codes with the performance of approaching the limit of Shannon. Because of its excellent performance, LDPC codes are widely used in wireless communication field and become one of the 4th generation mobile communication standards. The research on its application in the field of free space optical communication also has great space for mining. This paper first introduces the relevant theoretical knowledge of atmospheric laser communication. After introducing several basic channel models, the noise in the atmosphere is analyzed in detail. The model of atmospheric channel is given, which synthesizes the interference of various atmospheric turbulence channel noise to the communication link. The Gamma-Gamma distribution, which is consistent with the measured data, is used as the channel model. The structure of the LDPC code and the construction of the check matrix and several iterative decoding algorithms of the LDPC code are studied, including the probabilistic BP algorithm and the logarithmic BP(LLR BP algorithm. This paper presents an improved algorithm based on normalized minimum sum algorithm, normalized minimum sum algorithm, iterative APP algorithm and so on. The complexity and performance of each decoding algorithm are compared and simulated in various turbulent intensity channels. Then several decoding algorithms are simulated and compared on the Gamma-Gamma channel model. Compared with the minimum sum algorithm, the performance of the improved algorithm is improved. Finally, the influence of the number of iterations and code length on the decoding performance is discussed.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN929.1;TN911.22

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