【作者】 杨蓓；

【导师】 徐大专；

【作者基本信息】 南京航空航天大学 ， 通信与信息系统， 2005， 硕士

【摘要】 移动通信的飞速发展和新业务的不断出现,对移动通信系统的设计提出了更高的要求:如更大系统容量、更高信号质量和多媒体通信业务。为了满足这些要求,必须采用先进的多址接入方式和高级数字信号处理技术。九十年代初期,智能天线技术被应用于移动通信系统,这是移动通信系统中重要的技术突破,目前已被确立为第三代移动通信系统的核心技术之一,其概念也泛化为空时二维信号处理。本文研究了 CDMA 系统中的空时二维处理技术,主要包括波束形成技术,空时 2D-RAKE 接收机,空时多用户检测以及空时编码技术。全文的主要工作如下: 简单介绍了 CDMA 技术的特点,回顾了基于智能天线的空时处理技术的研究和发展概况。 基于均匀线阵的阵列模型,讨论了空时信道和空时信道模型,给出了空时信号的一般表达形式。 在对传统的广义旁瓣抵消波束形成技术研究的基础上,提出了一种基于特征结构的广义旁瓣抵消算法(ES-GSC),实验仿真表明这种算法对噪声具有鲁棒性。针对采样矩阵求逆算法(SMI)中存在的小特征值扰动问题,提出一种自适应的对角线加载的波束形成算法,大大提高了 SMI 算法的稳健性。同时,提出一种极大的抑制干扰的波束形成算法,由于这种算法与接收信号无关,仅仅和阵列天线的导向矢量有关,避免了矩阵求逆时的扰动问题,可以形成精确指向的方向图,对噪声有很好的鲁棒性,且在多径情况下仍有很好的波束形成性能。 在对空时 2D-RAKE 接收机的研究中,提出一种鲁棒的空时 2D-RAKE接收机算法,具有良好的误码率性能。同时,利用广义旁瓣抵消的思想提出一种空时 2D-RAKE 接收机,并给出其自适应的实现形式。实验表明具有良好的抗多径干扰和多址干扰的能力。 探讨了多径信道下的空时多用户检测。采用并行干扰相消(PIC)多用户检测的方法,结合空时 2D-RAKE 接收机提出空时并行干扰抵消(STPIC)多用户检测,并对 STPIC 算法进行了改进,采用部分并行干扰相消(PPIC)的空时多用户算法,同时采用新的判决函数代替传统的硬判决,实验仿真表明这种空时多用户检测方法在多径情况下的效果明显优于传统的空时多用户检测。 传统的下行链路发射分集的模型都是在假设到达天线的信号只存在单径分量的基础上建立的,但是实际上,信号存在多径分量。文中提出了 CDMA 下行链路的一种新的空时发射分集方案,在天线的发射端采用正交的扩频码,以解决传统方法中采用单一扩频码所带来的弊端,实验仿真结果表明,这种新的方法对抗多径的能力远远强于传统的方法,并且随着多径数的增加,误码率显著下降。更多还原

【Abstract】 With the fast development of mobile communications and emerging service, the design of mobile communication systems faces more challenges, for example, larger system capacity, higher signal quality and multimedia communications. In order to satisfy these requirements, we have to solve the problem by using advanced multiple access methods and digital signal processing. In early 90’s, smart antenna technique has been applied to commercial mobile communications; it is an important breakthrough in mobile communication techniques. Nowadays, smart antenna technique which is regarded as the core technique in 3G system,has been generalized to space-time signal processing. This thesis treats space-time processing in CDMA system. In this thesis, space-time 2D-RAKE receiver version, beamforming algorithms in transmitting mode, space-time multi-user detection and space-time coding are studied. The main contents are as follows: Introduces the characteristics and advantages of CDMA, and an overview of space-time processing in CDMA system. Based on uniform linear array (ULA) model, space-time channel and space-time signal are studied; a kind of model of space-time vector channel is given. Three kinds of new beamforming algorithms are proposed: firstly, A robust adaptive beamformer in the presence of array imperfections is presented by improving the block matrix of the generalized side lobe canceller (GSC), it is convenient to use its partial adaptive processing to reduce the computation load. Secondly, although sample matrix inversion algorithm (SMI) algorithm is sounded, the main problems is identified, the distortion of beam patterns occurred as a result of being hypersensitive to the perturbation during computing the covariance matrix inversion of received signal. In order to solve this problem, we propose an adaptive dialog-loading algorithm (ADL-SMI). The simulation results reveal that these two algorithms are robust to noise, and have good performance in beamforming. At last we develop another robust beamforming algorithm. The weight vector is only related with the steering vectors, and is independent of the received signal, so it can completely avoid to be influenced by the matrix perturbation when computing the covariance matrix inversion of received signal. Simulation results reveal that this new beamforming algorithm can form good beam pattern with low side lobe, and is robust to noise. In the thesis, two novel robust 2D-RAKE receivers are proposed. First 2D-RAKE receiver has two parts, one part is a new beamforming algorithm, which has been proposed in chart 3, and the other part is RAKE receiver. The simulation results show that this novel 2D-RAKE receiver can completely eliminate the multi-access interference (MAI) and resist the multipath interference. Secondly, We propose a space-time 2D-RAKE receiver with GSC, and give a adaptive version, The simulation results reveal that the new receiver precedes the conventional one in eliminating MAI and resisting multipath interference, and it can converge rapidly. Combined with smart antenna, space-time interference cancellation multi-user detection with multipaths channel is proposed. At the same time, hard decision is replaced by soft decision, and partial parallel interference canceller is given. Computer simulations illustrated that the performance of the algorithms proposed are much better than of traditional detection. Most modellings on space-time transmit diversity are based on the assumption that there is single-path arriving at the receive antenna from a transmit antenna. However, there are multipaths to arrive at the receive antenna from a transmit antenna in practice. A novel space-time transmit diversity scheme where orthogonal spread codes are used respectively at the transmit antennas is presented to solve this problem. Simulation results reveal that the space-time transmit diversity scheme presented in this paper have much better performance than conventional transmit diversity in multipath channel. We also find that this space-time transmit di更多还原