【摘要】：隨著無線移動(dòng)通信技術(shù)的不斷發(fā)展,人們對(duì)具有更好可靠性與有效性的通信傳輸技術(shù)的需求越來越大。現(xiàn)實(shí)生活中的無線信道,由于受到多徑傳播和衰落的影響,常被抽象成一種隨時(shí)間緩慢變化的信道模型一一塊衰落信道。近年來,構(gòu)造基于塊衰落信道具有良好碼性能和全分集的根校驗(yàn)的低密度奇偶校驗(yàn)碼(Root Check Low-Density Parity-Check, Root-LDPC)成為了研究熱點(diǎn)。基于邊擴(kuò)展(Progressive Edge-Growth, PEG)算法的基礎(chǔ)上,本文分析了幾種能夠影響Root-LDPC碼性能的主要因素,詳細(xì)介紹了陷阱集的圖形結(jié)構(gòu)及相關(guān)概念,并重點(diǎn)分析了陷阱集對(duì)Root-LDPC碼錯(cuò)誤平層及誤幀率的影響。大量研究表明：對(duì)Root-LDPC碼的糾錯(cuò)性能危害最大的陷阱集就是初等陷阱集(Elementary Trapping Sets, ETS)。在這些ETS中,那些尺寸較小的被稱為顯性初等陷阱集(Dominant Elementary Trapping Sets, dominant ETS)對(duì)Root-LDPC碼的錯(cuò)誤平層影響更大。而在顯性初等陷阱集的Tanner圖中基本不可能找到度數(shù)大于2的校驗(yàn)節(jié)點(diǎn),即幾乎所有Root-LDPC碼的顯性陷阱集都是初等陷阱集。為了解決這一問題,本文提出了一種塊衰落信道下基于陷阱集約束的PEG算法來構(gòu)造Root-LDPC碼。該算法將一種有效的初等陷阱集擴(kuò)展算法與傳統(tǒng)的PEG算法相結(jié)合。首先應(yīng)用PEG算法逐列構(gòu)造校驗(yàn)矩陣,然后利用初等陷阱集擴(kuò)展算法找到現(xiàn)有Tanner圖中尺寸較小的初等陷阱集并對(duì)其進(jìn)行擴(kuò)展,以此避免了顯性初等陷阱集對(duì)Root-LDPC碼性能的影響。仿真結(jié)果表明：利用該改進(jìn)算法構(gòu)造的Root-LDPC碼較原始及其他方法改進(jìn)的PEG算法具有更低的錯(cuò)誤平層和誤碼率。同時(shí),隨著碼長(zhǎng)減小,其誤幀率也隨之降低。然而,在運(yùn)行仿真的過程中,我們發(fā)現(xiàn)該改進(jìn)PEG算法是一種貪婪算法,隨著碼長(zhǎng)增大,編譯碼復(fù)雜度也隨之升高。準(zhǔn)循環(huán)算法(Quasi-Cyclic, QC)是一種結(jié)構(gòu)化的構(gòu)造算法,具有較低的編譯碼復(fù)雜度。因此,在基于陷阱集約束的PEG算法基礎(chǔ)上,本文提出了一個(gè)將QC算法與提出的初等陷阱集抑制PEG算法相結(jié)合的改進(jìn)算法。實(shí)驗(yàn)表明：該改進(jìn)算法與初等陷阱集抑制PEG算法具有相近的優(yōu)良編碼性能,相較現(xiàn)有PEG算法及其他改進(jìn)算法具有更低的錯(cuò)誤平層,并具有更短的運(yùn)行仿真時(shí)間,達(dá)到了碼的誤幀率性能和編譯碼復(fù)雜度的平衡,具有較強(qiáng)的應(yīng)用性。
[Abstract]:With the development of wireless mobile communication technology, there is a growing demand for more reliable and effective communication transmission technology. Due to the influence of multipath propagation and fading, wireless channels in real life are often abstracted into a fading channel model which changes slowly with time. In recent years, the construction of low-density parity-check codes (Root Check Low-Density Parity-Check, Root-LDPC) based on block fading channels with good code performance and full diversity has become a hot topic. Based on the edge expansion (Progressive Edge-Growth, PEG) algorithm, this paper analyzes several main factors that can affect the performance of Root-LDPC codes, and introduces the graphic structure and related concepts of the trap set in detail. The effect of trap set on Root-LDPC error level and frame error rate is analyzed. A large number of studies show that the primary trap set (Elementary Trapping Sets, ETS). Is the most harmful trap set to the error correction performance of Root-LDPC codes. In these ETS, the smaller size known as the dominant elementary trap set (Dominant Elementary Trapping Sets, dominant ETS) has more influence on the error level of Root-LDPC codes. However, it is almost impossible to find the check node with degree greater than 2 in the Tanner graph of the dominant elementary trap set, that is, almost all the dominant trap sets of Root-LDPC codes are elementary trap sets. In order to solve this problem, this paper proposes a PEG algorithm based on trap set constraints to construct Root-LDPC codes in block fading channels. This algorithm combines an effective elementary trap set expansion algorithm with the traditional PEG algorithm. First, the PEG algorithm is used to construct the checkout matrix, and then the elementary trap set extension algorithm is used to find and extend the small size elementary trap set in the existing Tanner graph, so as to avoid the influence of the dominant elementary trap set on the performance of Root-LDPC code. The simulation results show that the Root-LDPC code constructed by the improved algorithm has lower error level and bit error rate than the original and other improved PEG algorithm. At the same time, as the code length decreases, its frame error rate also decreases. However, in the course of running simulation, we find that the improved PEG algorithm is a greedy algorithm, and the complexity of encoding and decoding increases with the increase of code length. Quasi-cyclic algorithm (Quasi-Cyclic, QC) is a structured construction algorithm with low encoding and decoding complexity. Therefore, on the basis of PEG algorithm based on trap set constraint, this paper proposes an improved algorithm which combines the QC algorithm with the proposed elementary trap set suppression PEG algorithm. The experimental results show that the improved algorithm has similar excellent coding performance to the PEG algorithm, and has lower error level and shorter simulation time than the existing PEG algorithm and other improved algorithms. It achieves the balance of frame error rate performance and encoding and decoding complexity, and has a strong application.
【學(xué)位授予單位】：東北大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TN911.22

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