单载波频域均衡及其在短波通信中的应用

发布时间：2018-01-20 16:23

本文关键词： 单载波频域均衡短波特殊字判决反馈迭代块判决反馈均衡　出处：《中国舰船研究院》2014年硕士论文　论文类型：学位论文

【摘要】：短波通信在军事通信领域有着重要地位，是军事通信的主要方式之一。但是由于受到传输信道的影响，信号在接收端会产生严重的符号间干扰（Inter-Symbol Interference，ISI），从而影响系统性能。为了减小ISI的影响，通常采用正交频分复用（OrthogonalFrequency Division Multiplexing，OFDM）技术和单载波时域均衡（Single Carrier TimeDomain Equalization，SC-TDE）技术。但OFDM技术存在很高的峰均比（Peak-to-AveragePower Ratio，PAPR），并且对频率偏移和相位噪声十分敏感，SC-TDE的复杂度又随着时延扩展长度的增加变得难以接受。鉴于此，论文将单载波频域均衡（Single CarrierFrequency Domain Equalization，SC-FDE）技术作为研究对象。论文首先对短波通信及其宽带化作了简要介绍，，分析了短波信道的传输特性和两种常用的建模方法：窄带Watterson模型和宽带ITS模型。其次，论文分析了单载波频域均衡的基本原理，包括其系统框图和数学模型。同时介绍了单载波频域均衡系统中一种常用的帧格式和用作循环前缀的特殊字（UniqueWord，UW）序列。详细分析了特殊字序列的类型和产生方式，并对特殊字序列的包络、自相关函数和幅频特性进行了证明。然后，论文从理论上对单载波频域均衡系统和正交频分复用系统的峰均比、信道容量、误码性能以及对频率偏移和相位噪声的敏感度进行了详细分析和比较。接下来，论文重点分析了单载波频域均衡系统中的频域均衡算法，并分别进行了推导和仿真。常用的线性均衡算法有迫零（Zero Forcing，ZF）均衡和最小均方误差（Minimum Mean Square Error，MMSE）均衡。另外还有最小二乘（Least Square，LS）均衡，其缺点是需要多个训练序列，这大大降低了数据传输效率，因此并不常用。针对频域存在零点的信道，存在一类特殊字辅助的线性均衡算法，通过将特殊字序列和数据序列分开处理，能够有效缓解由此带来的性能恶化。为了进一步抑制噪声干扰和符号间干扰，混合判决反馈均衡（Hybrid DecisionFeedback Equalization，H-DFE）被提出。与之等价的还有一种被称为噪声预测判决反馈均衡（Noise Prediction Decision Feedback Equalization，NP-DFE）的结构，所不同的是噪声预测判决反馈均衡的前馈与反馈部分互相独立。残留符号间干扰消除（ResidualInter-Symbol Interference Cancellation，RISIC）算法也是一种判决反馈算法，它避免了矩阵求逆运算。最后，论文详细阐述了单载波频域均衡系统中的迭代块判决反馈均衡（IterativeBlock Decision Feedback Equalization, IBDFE）算法。这种算法的前馈和反馈部分均在频域进行，采用反馈加迭代的方式大幅提升了系统性能，但是其复杂度很高。虽然通过参数近似可以适当降低其复杂度，但这种近似存在参数模糊性，其性能很不稳定。为此，论文在IBDFE结构的基础上，利用最小均方误差准则，通过推导提出了一种新的简化算法，并进一步推导出了其噪声预测结构的等价形式。之后对现有低复杂度算法和所提出简化算法的均方误差（Mean Square Error，MSE）性能进行了理论分析，并对IBDFE结构下各种均衡算法的计算复杂度进行了比较。结果显示，所提出的简化算法大大降低了计算复杂度，同时，误码性能的仿真表明，所提出的简化算法在误码率方面相比传统算法有一定减损。
[Abstract]:Shortwave communication plays an important role in the field of military communication, is one of the main ways of military communication. But due to the impact of the transmission channel, the signal generated serious inter symbol interference at the receiving end will (Inter-Symbol Interference, ISI), which affects the performance of the system. In order to reduce the influence of ISI, usually using orthogonal frequency division multiplexing (OrthogonalFrequency Division Multiplexing, OFDM) technology and single carrier time domain equalization (Single Carrier TimeDomain Equalization, SC-TDE). But OFDM technology has very high peak to average ratio (Peak-to-AveragePower, Ratio, PAPR), and is very sensitive to frequency offset and phase noise, the complexity of the SC-TDE and with the increase of the length of delay spread is not accepted in view. In this paper, the single carrier frequency domain equalization (Single CarrierFrequency Domain Equalization, SC-FDE) technology as the research object.
This paper briefly introduces shortwave communication and broadband technology, analyzes the transmission characteristics of HF channel and two commonly used modeling methods: narrow band Watterson model and broadband ITS model.
Secondly, this paper analyzes the basic principle of the single carrier frequency domain equalization, including its system diagram and mathematical model. At the same time introduces a common frame format in single carrier frequency domain equalization system and used as a special word cyclic prefix (UniqueWord, UW) sequence. A detailed analysis of the special type of word sequence and generating, and envelope the special word sequence, autocorrelation function and amplitude frequency characteristic are proved.
Then, the paper theoretically analyzes and compares the peak to average power ratio, channel capacity, BER performance and sensitivity to frequency offset and phase noise of single carrier frequency domain equalization system and orthogonal frequency division multiplexing system.
Next, this paper focuses on the analysis of frequency domain equalization in single carrier frequency domain equalization system, and respectively are deduced and simulated. The linear equalization algorithm commonly used with zero forcing (Zero Forcing, ZF) equilibrium and minimum mean square error (Minimum Mean Square Error, MMSE). In addition to the least squares equalization (Least Square, LS) equilibrium, the disadvantages of the requirement of a training sequence, which greatly reduces the data transmission efficiency, so it is not commonly used. Based on frequency domain channel are zero, there is a linear equalization algorithm for a class of special auxiliary word, the special word sequences and data sequences separately, can effectively alleviate the performance degradation of the resulting.
In order to suppress the noise interference and intersymbol interference further, hybrid decision feedback equalization (Hybrid DecisionFeedback Equalization, H-DFE) is proposed. The equivalent one is known as the noise prediction decision feedback equalization (Noise Prediction Decision Feedback Equalization, NP-DFE) structure, which is different in the noise prediction decision feedback equalization of feedforward and feedback some are independent of each other. The residual inter symbol interference cancellation (ResidualInter-Symbol Interference Cancellation RISIC) algorithm is a kind of decision feedback algorithm, it avoids the computation of matrix inversion.
Finally, the paper elaborates on the iterative block decision in SC-FDE system (IterativeBlock Decision Feedback Equalization feedback equalization, IBDFE) algorithm. This algorithm feedforward and feedback part in the frequency domain, using feedback and iterative way greatly improves the system performance, but its complexity is very high. Although the parameter approximation may be appropriate to reduce its complexity, but the approximate parameters are fuzzy, the performance is very unstable. Therefore, based on the IBDFE structure, using the minimum mean square error criterion is proposed by a new simplified algorithm is deduced to predict the structure of equivalent form of noise. The mean square error of the existing low complexity of the proposed algorithm and simplified algorithm (Mean Square Error, MSE) performance of the theoretical analysis and calculation of various equalization algorithm under IBDFE structure The complexity is compared. The results show that the proposed algorithm greatly reduces the computational complexity. Meanwhile, the simulation of BER performance shows that the simplified algorithm has a certain reduction in bit error rate compared with the traditional algorithm.

【学位授予单位】：中国舰船研究院
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN925

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