【作者】 张炜；

【导师】 戴旭初；

【作者基本信息】 中国科学技术大学 ， 通信与信息系统， 2008， 博士

【摘要】 盲均衡是补偿通信信道失真、提高通信质量的一个关键技术。自从Y.Sato在1975年首次提出盲均衡的思想和算法以来,盲均衡技术受到了极大关注,众多学者对盲均衡器原理和算法进行了深入系统的研究,获得了大量的研究成果。目前,盲均衡技术已经在中低速的广播式通信系统、非合作式通信信号接收和处理等系统中获得了成功的应用。近年来,随着无线通信朝着高速、宽带方向的快速推进,现有的一些单载波通信系统的通信速率不断提高,传输信号的带宽不断增大,如一些近地卫星通信系统和地面的微波通信系统的传输速率达到10~2～10~3Mbps量级。在如此高速的无线通信系统中,宽带传输信道的多径延迟扩展可能会导致上百个符号间的干扰。一方面,采用现有的盲均衡器结构和算法对长冲激响应信道进行均衡时,要求均衡器的抽头数很大;另一方面,宽带信道的频谱在通带内起伏变化也较大;由于这两个原因导致采用传统结构的盲均衡器收敛速度缓慢,而且实现的复杂度也较高,难以满足实时处理的应用需求。目前,如何解决宽带单载波通信中盲均衡器的收敛速度慢、实现复杂度高的问题还没有一个成熟的解决思路和方案。本文以单载波传输体制的高速通信系统为对象,以非合作条件下通信信号接收和处理为应用背景,以提高盲均衡器的收敛速度和算法的实时实现性为目标,对宽带线性盲均衡器结构和算法进行深入的分析和研究。其主要的贡献是采用子带自适应滤波的思想,将多速率滤波器组引入到传统的线性盲均衡器中,提出了几种适合于单载波通信系统的宽带线性盲均衡器的新结构、实现方法以及相关的算法,并对它们的性能进行了深入细致的分析和研究。本文的主要创新点有:一、提出了一种基于均匀子带分解的宽带线性盲均衡器将均匀子带分解技术应用于传统的线性盲均衡器,给出了一种适合于高速宽带通信的盲均衡器结构及算法。该结构将子带均衡器系数更新和全频带的子卷积方法有机结合在一起,明显地加快了高速宽带传输条件下线性盲均衡器的收敛速度,而且通过并行处理降低了对处理时间的要求,改善了线性盲均衡算法的实时性。根据子带盲均衡器结构的特点,对传统的停止-前进(Stop-and-Go,SAG)类算法进行了改进,通过将算法的判决过程分离到子带中进行,消除了由于子带分解而引入的记忆误差,实验结果表明,改进后的子带SAG算法收敛速度有了明显的提高。二、提出了一种分数间隔的宽带线性盲均衡器将分数间隔恒模算法(FSE-CMA)和子带分解技术结合起来,给出了一种分数间隔的宽带线性盲均衡器结构。子带分解的预白化作用能明显加快FSE-CMA的收敛速度;同时,子带分解和子卷积方法都允许对数据进行降速率的并行处理,有利于算法的实时实现。三、提出了一种基于信号功率谱幅度分割的非均匀滤波器组基于功率谱幅度分割的思想来设计非均匀滤波器组,是非均匀滤波器组设计的一个新方法。其主要特点是能有效地降低子带信号自相关矩阵的特征值扩散度,从而提高子带最小均方(LMS)自适应算法的收敛速度。在详细地描述了其设计思想的基础上,给出了非均匀子带定位算法、非均匀滤波器组的设计过程和主要参数选择。理论分析和实验仿真表明,该滤波器组不仅能有效地降低子带信号自相关矩阵的特征值扩散度,并且具有良好的信号重建特性。四、提出了一种基于非均匀子带分解的宽带线性盲均衡器将基于信号功率谱幅度分割的非均匀子带分解方法应用于子带盲均衡器中,给出了一种基于非均匀子带分解的宽带线性盲均衡器结构和算法,其主要的特点是能够根据宽带信道的幅频特性动态地调整非均匀子带的带宽和位置,相比于均匀子带分解的盲均衡器,能更有效地降低子带信号自相关矩阵的特征值扩散度,从而能进一步提高子带线性盲均衡算法的收敛速度。另外,针对非均匀子带信号具有不同采样率的特点,综合考虑收敛速度和运算复杂度两方面的因素,给出了非均匀子带均衡器系数更新的一个有效的策略,在获得收敛速度提高的同时,还能很好地控制运算复杂度。更多还原

【Abstract】 Blind equalization is one of the key technologies to compensate for channel distortion and enhance the communication quality. Since Y. Sato first introduced the idea and algorithm of blind equalization in 1975, the blind equalization technique has attracted great attentions. Many researchers have made in-depth studies on the principles and algorithms of blind equalization, and got a lot of research results. At present, blind equalization has found applications in medium-speed or low-speed broadcast communication systems, receiver of non-cooperative communication systems, and so on.In the recent years, with the rapid development of the high-speed wideband wireless communication, the date rates and transmission bandwidth of the existing single-carrier communication systems are gradually increasing. For example, some low earth orbit satellite communication systems and terrestrial microwave communication systems have gotten the transmission rate up to 10~2-10~3 Mbps. In such a high-speed wireless communication system, the wideband transmission channel’s delay spread may cause intersymbol interference between hundreds of symbols. On the one hand, when the existing structure and algorithms of blind equalizers are used, a large number of taps are required to equalize the channel. On the other hand, the spectrum of the wideband channel will dramatically fluctuate in the passband. The two factors will cause slow convergence speed as well as high implementation complexity of the traditional blind equalizer, which doesn’t meet the need of real-time processing applications. And so far, there is no mature idea or scheme to deal with these problems.In this dissertation, the structures and algorithms of wideband blind linear equalizer are deeply studied, to improve the convergence speed and real-time realization of blind equalization in high-speed, single carrier no-cooperative communication systems. The main contribution of this dissertation is that, based on the idea of subband adaptive filters, several novel wideband blind linear equalizers are proposed, which is suitable for single carrier communication system. In addition, the performance of these wideband linear blind equalizers is analyzed in detail.The main innovations of this dissertation are listed as follows. 1. Propose the uniform subband decomposition based wideband blind linear equalizerA new structure and algorithm of blind equalizer suitable for high-speed wideband communication are proposed by introducing uniform subband decomposition technique into the traditional blind linear equalizer. The proposed blind equalizer effectively combines the subband decomposition technique and sub-convolution method, and its convergence speed is faster than that of the traditional blind equalizer. On the other hand, parallel computation reduces the processing time, which is propitious to the algorithm’s real-time realization.The tradition stop-and-go (SAG) algorithm is modified, according to property of the subband structure. It eliminated the memory error caused by subband decomposition, by separating the decision process into each subband. Experimental results prove that the convergence speed of the modified subband SAG algorithm is effectively improved.2. Propose a fractionally spaced wideband blind equalizerA fractionally spaced wideband blind equalizer is proposed by combining the fractionally spaced constant modulus algorithm (FSE-CMA) with the subband decomposition technique. The pre-whiten effect of the subband decomposition can significantly improve the convergence speed of FSE-CMA. Meanwhile, since the down-sampling and parallel processing of the subband decomposition as well as the sub-convolution are used, the proposed equalizer is beneficial to its real-time realization.3. Propose a non-uniform filter bank designed by the criterion of power spectrum amplitude segmentationIt is a novel method to design non-uniform filter bank based on the idea of power spectrum amplitude segmentation. The key feature is that it can effectively reduce the eigenvalue spread of auto correlation matrices of the subband signals, thus obviously improve the convergence speed of the subband least mean square (LMS) algorithm.The design method of the non-uniform filter banks is discussed in detail, including the algorithm of non-uniform subband allocation, the structures and the main design parameters of the filter bank. Theoretic analysis and simulation results show that the proposed non-uniform filter bank can effectively reduce the eigenvalue spread of auto correlation matrices of the subband signals, and possesses better performance of reconstructing the original signal4. Propose the non-uniform subband decomposition based wideband blind linear equalizerA structure and algorithm of wideband blind linear equalizer based on non-uniform subband decomposition is proposed, which utilizes the non-uniform subband decomposition method based on the idea of power spectrum amplitude segmentation. The main feature is that it can dynamically adjust the location and bandwidth of the subbands, and reduce the eigenvalue spread of auto correlation matrices of the subband signals more effectively than the one based on uniform subband decomposition. As a result, the convergence speed of the blind equalization algorithm can obviously be quickened.In addition, as the non-uniform subband signals have different sampling rates, an adapting strategy of the non-uniform subband equalizers is derived, which can effectively compromise between the convergence speed and computational complexity. By using the strategy, the equalizer can improve the convergence speed, and simultaneously reduce the computational complexity.更多还原