【作者】 杨闽；

【导师】 戴居丰；

【作者基本信息】 天津大学 ， 通信与信息系统， 2010， 博士

【摘要】 正交小波包复用(OWPM)作为多载波系统的一个新兴技术越来越受到研究者的关注,它利用小波包逆变换和正变换实现多载波信号的调制和解调。具有频谱利用率高,抗干扰能力强,易于实现多速率传输等特点。信道估计是实现OWPM系统高速率传输的关键技术之一,所以对于OWPM系统及其信道估计等关键技术的研究具有重要的研究意义和实用价值。本文在系统分析OWPM原理的基础上,深入研究了在多径衰落信道下适用于OWPM系统的信道估计新方法。主要工作与贡献如下:(1)针对OWPM缺乏完整论述的现况,系统总结了OWPM系统的基本原理。结合小波理论和波形正交的特性,着重分析了OWPM系统的正交性;并就多路复用转换器在多载波系统中的应用,给出了正交小波包复用系统任意分解模式下,多速率滤波器组的实现方式。对OWPM系统在多径衰落信道中的性能进行仿真分析。(2)提出了在二维时频域中不等间隔插入导频的信道估计方法。针对传统的导频模式并不适用于OWPM系统的问题,文中分别就OWPM系统逐级分解模式和全载波分解模式两种情况提出了适用于OWPM系统的导频模式。在逐级分解模式下,根据不同子载波码元周期互不相同的特点,提出了随着分解尺度的加深,以等比数列模式逐级减少导频间隔的导频模式。在全载波分解模式下,根据不同频率对相干时间的影响,提出了将子载波在二叉树的基础上进行分组,随着频率的增加,以等差数列模式依次减少每个分组的导频间隔的导频模式。仿真结果表明:上述两种方法实现了导频的合理分配,并提高了估计精度。(3)提出了基于EM半盲信道估计方法的优化补偿算法。针对EM算法存在的误差传播问题,提出了在E步和M步迭代过程中,利用线性内插进行二次估计的补偿算法,并利用相邻子载波之间的相关性降低算法复杂度。该方法兼顾了各个子载波分量在时域和频域的相关性,有效地提高了EM算法的精度,加快了算法的收敛速度。(4)提出了利用抗差估计抑制符号间干扰和信道间干扰的抗差信道估计方法。针对带有符号间干扰和信道间干扰的OWPM系统服从非高斯噪声分布的特性,提出了基于Huber抗差迭代的信道估计方法。所提方法根据噪声的大小分别采用LS估计和L1估计,有效地抑制了ISI和ICI的对系统造成的影响,并在一定程度上简化了系统均衡算法的复杂度。更多还原

【Abstract】 Orthogonal wavelet packet division multiplexing (OWPM) is one of multicarrier transmission systems. It realizes the modulation/demodulation of transmission signal using wavelet packet transform. OWPM system supports high bandwidth efficiency, little affect of interference and multirate wireless transmission. For the sake of high-speed transmission, channel estimation is one of the key technologies of OWPM system. So the researches of OWPM system and its channel estimation technical are very important and useful.On the basis of summarizing the theory of OWPM system, this thesis researches the channel estimation methods which fit for OWPM system under multi-path fading environment. Our contributions are concluded as follows:Because of the lack description of OWPM, a complete understanding of OWPM system is provided. First, the orthogonality of OWPM system is analyzed with the theory of wavelet transform and waveform orthogonality. Then, with the application of transmultiplexers in multicarrier communications, the realization of OWPM system which with arbitrary subchannel separation in terms of multirate filters is described. At last, the performance of OWPM under fading channel is presented.A method of inserting pilots with unequal interval is explored. Aim to the traditional pilot arrangement is not suitable for OWPM systems, two kinds of unequal pilot mode are emphasized. In the type of decomposition step by step, the pilot mode according to the different periods of symbols which belong to different decompose-level is proposed. Use geometric sequence to realize the unequal pilot arrangement. The deep decoposion-level is, the little pilots are inserted. In the type of full decomposition, the pilot mode according to the influence on the coherent time caused by frequency-domain characteristic is proposed. The method divides subcarrier into groups and use arithmetic theory to realize the unequal pilot arrangement. Simulation results indicate that the proposed methods realize the pilot arrangement optimally and perform excellent in multi-path fading channel.An optimal and compensated expectation-maximization algorithm based channel estimation method is proposed to minimize the effect of error propagation during estimation. Linear interpolation is introduced to do quadratic estimation between E-step and M-step, and the correlationship of subcarrier is used to reduce the complexity.With utilization of the coherence between the time and frequency domain of each subcarrier, the algorithm accuracy is improved and the convergence is accelerated.A robust channel estimation method using robust estimation theory is presented to mitigate inter-symbol interference (ISI) and inter-channel interference (ICI). Because OWPM system model with ISI and ICI is followed non-Gaussion distribution, a Huber interative estimation mehtod is introduced to the channel estimation. According to the different noise values, LS estimation and L1 estimation are used respectively. Simulation results show that ISI and ICI can be reduced effectively.更多还原