DS-CDMA系统基于高阶累积量的盲波束形成及DOA估计

依据DS-CDMA系统的扩频码和扰码特性,提出了一种新的基于高阶量的盲波束形成算法,然后根据得到的波束形成权值实时估计信号波达方向(DOA)。该方法充分利用了接收信号的高阶统计特性,在高斯有色噪声及非高斯噪声信道环境下具有良好的性能。另外,该算法不需要已知信道参数和训练序列等先验知识,收敛速度较快,适合在实际信道环境中的应用。     

异步DS-CDMA系统子空间盲特征波形估计算法的鲁棒性问题研究

 本文针对异步DS-CDMA系统,在理论上分析了信道阶、信道头和尾对子空间盲特征波形估计算法性能的影响,并进行了计算机仿真.首先提出了一个特征波形分解模型,将特征波形分解为m阶主要部分和次要部分,得到了相应的m阶子空间算法;然后运用矩阵扰动理论,证明了特征波形分解的可行性,即m阶子空间算法的特征波形估计逼近于m阶主要部分;最后从矩阵特征值分解的稳定程度出发,推导了特征波形分解准则,该准则指出应该避免考虑次要部分,采用尽可能小的信道阶.仿真结果验证了理论分析的正确性.     

A Low Complexity Downlink Beamforming Scheme for DS-CDMA System

The downlink capacity of frequency division duplex (FDD) based DS-CDMA system can be improved if multielement antenna array is equipped at the base station. In this paper, a novel two-path downlink beamforming (TPDB) scheme is proposed to reduce multiple access interference as well as providing two-order path diversity in downlink. An analysis model is presented for the capacity evaluation of multirate DS-CDMA system with base station antenna array, and the capacity performance of the TPDB is compared with other schemes based on this model. The comparison results show that the TPDB would be a promising candidate for the downlink transmission if both performance and implementation complexity are considered. Moreover, a simple algorithm is proposed for the steering vector estimation in the TPDB, and the robustness of this estimation algorithm in the presence of fading and interference is also confirmed by computer simulations.     

Precoding for Minimization of Envelope Variations in Multicode DS-CDMA Systems

A multicode direct-sequence code-division multiple-access system experienceslarge envelope variations as a result of a sum of many independently spreadsignals. However, large envelope variations is problematic because it reducesthe spectral efficiency, the efficiency of the power amplifiers and theperformance. All these effects depend on the non-linear amplifiers thatgenerally are used in handsets. It would of course be possible to use a linearamplifier but then the power efficiency is drastically reduced. In this paperwe analyze the envelope variations of a multicode signal in terms of thecrest factor and find that it increases as the square root of thenumber of used codes. As a consequence it is only possible to use themulticode scheme for a few parallel codes. To reduce the envelope variationsa precoder is introduced. This precoder is a non-linear high-rate block codeespecially designed for the set of spreading codes used. However, the precodercan be made independent of the spreading codes if a user-specific spreadingcode is concatenated with a set of Hadamard or Conference sequences. Theresulting spreadig codes are orthogonal. Also, the precoder is independent ofthe user-specific spreading code, and can thus be used for all users. Afterprecoding the crest factor is significantly reduced and the performance, dueto introduced coding gain, improved. Algorithms for the design of precoderswith both reduced envelope variation and good performance are presented.Furthermore, simulations show that a precoded multicode system outperforms anuncoded multicode system in a single-user as well as in a multiuserenvironment.     

适用于MC DS-CDMA信号的定时同步算法

提出了一种适用于MC DS-CDMA信号的定时同步方案.该方案针对MC DS-CD-MA系统的特点,通过频域相关器输出矢量旋转同时获得多个同步检测统计量的近似值,既提高了捕获性能,又成倍降低了定时跟踪算法复杂度.理论分析和数值结果证明了方案的可行性.     

采用DS-CDMA方式的超宽带技术研究与应用

对超宽带（UWB）技术的起源和在现阶段的发展概况进行了阐述,讨论了DS-CDMA实现方式的技术特点,通过对技术参数的分析,说明了DS-UWB技术的利弊所在,同时介绍了DS-UWB当前的应用情况和发展前景。     

一种基于伪卫星跳时信号的联合捕获算法

地基伪卫星系统为克服远近效应影响，通常采用跳时(Time Hopping/Direct Sequence-Code Division Multiple Access, TH/DS-CDMA)信号进行伪距测量与定位，导致接收终端必须增加系统跳时序列相位估计的设计，降低捕获效能的同时也引入了接收终端的捕获复杂度。针对以上问题，提出了一种基于伪卫星跳时信号的联合捕获算法，利用跳时信号的时域正交特性与时隙分配特点，将多基站单脉冲信号捕获结果映射为使能时隙序列，通过循环截断相关完成跳时参数估计，有效缩短了跳时参数估计时间。仿真结果表明，该方法能够正确完成捕获阶段的参数估计，4个伪卫星的联合捕获耗时相较传统方法减少63.32%,为伪卫星跳时信号的快速捕获提供了有效方法。