【作者】 谢晓红；

【导师】 王华奎；

【作者基本信息】 太原理工大学 ， 通信与信息系统， 2007， 硕士

【摘要】 智能天线技术是第三代移动通信系统中的关键技术之一。智能天线技术引入了空分多址(Space Division Multiple Access，SDMA)方式，利用信号不同的空间传输路径，可以将相同频率、相同时隙、相同地址码的信号区分开来，并能够与其他多址技术相结合，使得通信资源由时间域、频率域和码域扩展到了空间域，从而有效地增大了系统容量，最大限度地利用了有限的频谱资源。在频分双工(FDD)系统中，由于上、下行载波的频率差大于相干频带，上、下行信道衰落是不相关的，而且阵列响应也与信号的载波频率有关，因此，上行信道不能直接用来估计下行信道，故智能天线应用于下行链路是一个难点。但是，如果上、下行载波频率间隔不是太大，下行波束形成可以利用上行链路的DOA信息来实现。本文选择智能天线中DOA估计算法进行研究。本文主要工作概括如下：1．建立上下行链路信道模型，据此获得FDD系统中DCCM的计算公式。2．MUSIC等高分辨率算法在估计DOA时需要进行协方差矩阵的特征分解运算，但是传统的矩阵特征分解方法计算量都非常大，不适合实时运算。另外，MUSIC算法不能很好地估计出弱信号的DOA，通过仿真结果证明确实是这样。3．本文提出了基于改进PCA的DOA估计方法，在原有MUSIC算法的基础土引入了迭代估计信号子空间的方法，代替了原算法中通过特征值分解获得信号子空间的部分。仿真表明，本文提出的算法在估计弱信号时性能比较好，而且与MUSIC算法相比，计算复杂度有所降低，这可以从学习曲线上看出。4．在DOA估计的基础上，本文首先综合了文献[47-50]中的主要思想，然后对其进行了详细的数学推导，之后，据此得到了下行发射波束形成的初始权值。在此基础上以最小化阵列发射功率为目标对初始权值进行优化得到了优化权值。最后通过仿真验证比较了初始权值和优化权值应用于下行波束赋形对方向图的影响。更多还原

【Abstract】 Smart antenna technology is one of the key technologies of the thirdgeneration mobile communication system. And it introduces space divisionmultiple access which makes use of different transmission paths ofdifferent signals to differentiate the signals from the same frequency, thesame time slot and the same code. Moreover, space division multiple accesscan also be combined with other multiple access technologies, such as timedivision multiple access, code division multiple access, and so on. Smartantenna technology makes the range of communication resource extendfrom time region, frequency region and code region to space region. Thussmart antenna can remarkably increase the capacity of communicationsystem, and sufficiently exploit limited frequencY spectrum resource. In anFDD wireless system, the duplex spacing between uplink and downlink islarger than the coherence bandwidth of the mobile radio channel, thus theuplink and the downlink small-scale fading is uncorrelated. Moreover, thearray response is correlated with the frequency of the signal carrier. So it isimpossible to resue the uplink weights for downlink beamforming. As aresult, the application of smart antenna for the downlink is a difficult problem. However, if the duplex spacing between the uplink and thedownlink isn’t large enough, the uplink channel parameters like thedirections-of-arrival can be used for the downlink beamforming. This paperplaces its importance on the research of DOA estimation algorithms.The major works of this paper can be summarized as follows:1. This paper establishes the uplink and downlink channel model.According to this model, it knows how to calculate DCCM.2. Many high resolution subspace-based methods like MUSIC andESPRIT estimate the direction of arrival of plane waves impinging on anantenna array via eigendecomposition in array signal processing. However,high computational burden for eigendecomposition makes them unsuitablefor real time processing. Moreover, MUSIC algrithom can’t estimate weaksignals very well, and it is verified through the simulation.3. This paper presents a DOA estimation method based on a novelprincipal component analysis technique. It introduces an iterative approachfor estimating the signal subspace to MUSIC algorithm, which substitutesthe steps that obtain signal subspace via eigendecomposition in originalalgorithm. Simulation results show that the proposed algorithm has betterperformance than MUSIC algorithm when estimating weak signals and itscomputational complexity is smaller, which can be seen from the learningcurves.4. On the basis of DOA estimation, this paper integrates the mainideas in literatures[47-50] firstly, and then deduces them in detail, after thatthis paper achieves the initial weight according to those results deduced.Based on these works finished before, aiming to minimize the arraytransmission power, it optimizes the initial weight and gains optimized weight. In the end, through the simulation this paper compares their effectson the beam pattern when initial weight and optimized weight are used forthe downlink beamforming.更多还原