【摘要】：高速移動的寬帶無線通信系統(tǒng)是未來無線通信發(fā)展的明顯趨勢,其中移動性是現(xiàn)有和未來無線通信、車輛網(wǎng)絡(luò)、高速鐵路等系統(tǒng)所具有的重要屬性。更高的通信帶寬和移動速度使得信號經(jīng)歷的通信信道更為復(fù)雜多變,信道表現(xiàn)出明顯的時間色散和頻率色散雙選擇性衰落特性。如何適應(yīng)雙選擇性衰落信道快速多變的復(fù)雜特性,保證通信的可靠傳輸,提高通信傳輸效率是未來移動通信需要解決的關(guān)鍵技術(shù)之一。本文圍繞無速率編譯碼技術(shù)和Vector OFDM調(diào)制技術(shù)開展研究,主要研究內(nèi)容概括如下。本文分析了雙選擇性衰落信道的BEM模型,提出雙選擇性衰落信道下的自適應(yīng)Vector OFDM系統(tǒng)。與傳統(tǒng)固定調(diào)制方式和循環(huán)前綴的Vector OFDM系統(tǒng)不同,自適應(yīng)Vector OFDM系統(tǒng)在給定誤碼差錯閾值的條件下,通過估計信道條件信息(CSI)自適應(yīng)變換域信號的調(diào)制方式和二維循環(huán)前綴長度。采用自適應(yīng)機(jī)制,在信道條件好的情況下可以大幅度提高每符號承載消息比特數(shù)目。由于雙選擇信道的分集受到信道自由度、碼率、向量長度等諸多因素影響,自適應(yīng)Vector OFDM在改交碼率,提高傳輸效率的同時,能夠提高聯(lián)合多徑-多普勒分集增益,降低比特差錯概率。本文研究了無速率碼的度數(shù)分布特征,提出了基于信號空間分集的無速率碼聯(lián)合度數(shù)譯碼規(guī)劃設(shè)計。與一般編碼映射機(jī)制不同,該方法受至Underboeck提出的信號空間分集思想啟發(fā),通過信號空間分集逐層增大信號空間子層相鄰星座點的歐氏距離,映射符號的比特具有不同的置信度期望。潛在的比特不等差錯保護(hù)使得接收端可以不用比較接收端符號置信度大小,更加迅速地迭代更新接收消息的對數(shù)似然信息LLR。文章分析了16QAM和64QAM信號空間分集的誤比特率以及來自信道的對數(shù)似然信息,并給出了一般高階調(diào)制無速率碼譯碼規(guī)劃詳細(xì)的方案設(shè)計。該方案可以在不需要額外的帶寬開銷和降低碼率的前提下,提高譯碼性能,顯著降低誤碼率。本文最后結(jié)合無速率碼和Vector OFDM調(diào)制,設(shè)計了聯(lián)合編碼調(diào)制方法以對抗雙選擇性衰落信道�；趶V義無速率碼分組碼,文章理論分析了度數(shù)分布對譯碼復(fù)雜度和譯碼差錯概率的影響,得出兩點結(jié)論,即當(dāng)分組無速率碼的平均度數(shù)相等時譯碼復(fù)雜度最低,同時譯碼成功概率最大。根據(jù)兩點結(jié)論以及雙選擇信道分集理論,提出了兩種編碼調(diào)制方案,一種是基于度數(shù)均勻分布的聯(lián)合編碼調(diào)制,另一種基于遍歷雙選擇信道子信道以獲取聯(lián)合多徑-多普勒分集增益的編碼調(diào)制機(jī)制。與普通的無速率碼串聯(lián)Vector OFDM系統(tǒng)相比,兩種編碼調(diào)制方案均可以提高系統(tǒng)性能,降低誤比特率。
[Abstract]:High speed mobile broadband wireless communication system is an obvious trend of wireless communication in the future, in which mobility is an important attribute of existing and future wireless communication, vehicle network, high-speed railway and other systems. The higher communication bandwidth and moving speed make the communication channel more complex and changeable. The channel shows obvious dual selective fading characteristics of time dispersion and frequency dispersion. How to adapt to the complex characteristics of double-selective fading channels, ensure reliable transmission of communication and improve the transmission efficiency are the key technologies to be solved in future mobile communications. This paper focuses on the rate-free coding and decoding technology and Vector OFDM modulation technology, the main research content is summarized as follows. In this paper, the BEM model of dual selective fading channel is analyzed, and an adaptive Vector OFDM system is proposed for dual selective fading channel. Different from the conventional Vector OFDM system with fixed modulation mode and cyclic prefix, the adaptive Vector OFDM system estimates the modulation mode of the (CSI) adaptive transform domain signal and the 2-D cyclic prefix length by estimating the channel condition information under the given error threshold. The adaptive mechanism can greatly increase the number of message bits per symbol under good channel conditions. Due to the influence of channel freedom, bit rate, vector length and so on, the adaptive Vector OFDM can improve the joint multipath Doppler diversity gain while improving the transmission efficiency. Reduce bit error probability. In this paper, the degree distribution characteristics of rate free codes are studied, and the joint degree decoding planning design of rate free codes based on signal space diversity is proposed. Different from the general coding mapping mechanism, this method is inspired by the idea of signal space diversity proposed by Underboeck, and increases the Euclidean distance of adjacent constellation points in signal space sublayer by signal space diversity layer by layer. The bits of the mapping symbols have different confidence expectations. Potential bit unequal error protection makes it possible for the receiver to iterate over and update the logarithmic likelihood information (LLR.) of the received message more quickly without comparing the magnitude of the received symbol confidence. In this paper, the bit error rate (BER) of spatial diversity of 16QAM and 64QAM signals and the logarithmic likelihood information from the channel are analyzed, and the detailed scheme of decoding planning for general high-order modulation rate-free codes is given. The proposed scheme can improve the decoding performance and significantly reduce the bit error rate without additional bandwidth overhead and bit rate reduction. Finally, combining rate free code and Vector OFDM modulation, a joint coded modulation method is designed to counteract the dual selective fading channel. Based on the block codes of generalized rateless codes, the influence of degree distribution on decoding complexity and decoding error probability is analyzed theoretically, and two conclusions are drawn: the decoding complexity is the lowest when the average degree of block codes is equal. At the same time, the probability of successful decoding is the highest. Based on the two-point conclusion and the theory of dual-selection channel diversity, two coding modulation schemes are proposed, one is joint coded modulation based on uniform distribution of degrees. Another coding modulation mechanism is based on traversing dual selective channel subchannels to obtain joint multipath Doppler diversity gain. Compared with the conventional rate-free series Vector OFDM system, both coding and modulation schemes can improve the performance of the system and reduce the bit error rate (BER).
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TN929.53

【參考文獻(xiàn)】

相關(guān)期刊論文 前1條

1 Xiqian Luo;Zhaoyang Zhang;Caijun Zhong;Xinyu Jin;;Exploiting cooperative multipath Doppler diversity in relay-assisted high-speed train communications[J];Chinese Science Bulletin;2014年35期

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本文編號：2220249