A fast algorithm for joint two-dimensional direction of arrival and frequency estimation via hierarchical space–time decomposition

In this paper, we present a fast algorithm for joint estimation of the two-dimensional (2-D) directions of arrival (DOAs) and frequencies of the incoming signals in wireless communications using a hierarchical space–time decomposition (HSTD) technique. Based on the HSTD, the proposed algorithm makes use of a sequence of one-dimensional (1-D) Unitary estimation of signal parameters via rotational invariance technique (ESPRIT) algorithms to estimate these parameters alternatively in a hierarchical tree structure. Also, in between every other 1-D Unitary ESPRIT algorithm, a temporal filtering process or a spatial beamforming process is invoked to partition the incoming signals into finer groups stage by stage to enhance the estimation accuracy as well as to alleviate the contaminated noise. Furthermore, with such a tree-structured estimation scheme, the pairing of these parameters is automatically determined without extra computational overhead. Simulation results show that the new algorithm provides satisfactory performance but with drastically reduced computations compared with previous works.     

基于四粒子GHZ纠缠态实现双向隐形传态

提出了一种用四粒子GHZ纠缠态作为量子信道,实现量子双向隐形传态的方案。通信双方Alice和Bob事先共享俩对四粒子GHZ纠缠态。通信开始后,Alice和Bob分别对自己拥有的粒子作量子投影测量,并将测量结果通过经典信道告诉对方。Alice和Bob根据对方提供的测量结果,做相应的幺正变换,即在己方的粒子上再现对方要传的量子信息,从而实现整个双向传态的目的。只要通信双方事先选取合适的GHZ纠缠态作为量子信道以及分发不同对应的纠缠粒子即可分别实现单量子比特任意态、双量子比特Bell纠缠态和三量子比特GHZ纠缠态的双向隐形传态。     

酉空时调制系统中基于多符号差分检测的软检测器

该文设计了一种适用于差分酉空时调制体制的低复杂度软检测算法。该算法基于多符号差分检测,为软判决译码模块提供编码比特的对数似然比信息。仿真表明,在通常容许的误码范围内,采用所提出的软检测算法构建的差分酉空时调制系统比原硬判决系统节省2～4dB的信号功率,并解除了基于单符号差分检测的软检测算法在快衰落信道下的错误平层。     

一种降低接收机复杂度的差分空时调制方案

基于对角信号的差分酉空时调制技术不需要信道估计并能实现满天线分集,但接收机的计算复杂度与发射天线数和数据率成指数关系。该文针对发射天线数为偶数的系统,提出了一种降低接收机计算复杂度的差分空时调制方案。该方案将发射天线分成相等数目的两组并在每一组天线上分别进行对角酉空时调制,接着构造差分编码矩阵使得两个对角信号的最大似然检测可以分开进行,从而大大降低了接收机的计算复杂度。理论分析和仿真表明,该方案仍实现了满天线分集,并且对于某些应用环境能提供比对角信号更好的误比特率性能。     

Reduced-complexity decoding algorithms for unitary space-time codes

Two reduced-complexity decoding algorithms for unitary space-time codes based on tree-structured constellation are presented. In this letter original unitary space-time constellation is divided into several groups. Each one is treated as the leaf nodes set of a subtree. Choosing the unitary signals that represent each group as the roots of these subtrees generates a tree-structured constellation. The proposed tree search decoder decides to which sub tree the receive signal belongs by searching in the set of subtree roots. The final decision is made after a local search in the leaf nodes set of the selected sub tree. The adjacent subtree joint decoder performs joint search in the selected sub tree and its ＂surrounding＂ subtrees, which improves the Bit Error Rate （BER） performance of purely tree search method. The exhaustively search in the whole constellation is avoided in our proposed decoding algorithms, a lower complexity is obtained compared to that of Maximum Likelihood （ML） decoding. Simulation results have also been provided to demonstrate the feasibility of these new methods.     

RLC介观电路中的广义动量和动力学动量

用幺正变换的方法，求出了RLC介观电路中的广义坐标与广义动量、动力学坐标与动力学动量的测不准关系，从而发现前者与时间无关，后者与时间成指数关系。     

天然金刚石刀具在整体式波前校正器加工中的应用

单直线刃天然金刚石刀具在切削整体式波前校正器时可能会与待加工表面发生干涉。根据待加工表面的数学模型及刀具的运动轨迹,推导出单直线刃金刚石刀具加工波前校正器时与待加工表面不发生干涉的最小安装角的数学模型;根据光学加工表面微观不平度高度与刀具刃口参数及安装角之间的关系,推导出能满足给定表面粗糙度的刀具最大安装角。在超精密车床上进行了切削实验,结果表明,用单直线刃天然金刚石刀具切削整体式波前校正器是可行的。     

求解滚齿机挂轮的一种实用方法及Microsoft VisualC++6.0实现

基于差动挂轮计算方法,介绍了一种适合各种型号滚齿机的挂轮选择程序。它可以在最短的时间内实现给定精度下的挂轮组合。由于程序通用性好,修改个别的语句和参数,程序就能完成各种型号滚齿机的挂轮计算。     

基于W态的量子安全直接通信协议

提出了一种新的两方量子安全直接通信协议。该方案利用有序的四粒子W态作为信息载体,利用幺正变换对秘密消息进行编码,通过当地Bell基测量和经典通信直接传递秘密消息。在理想信道下,协议对于非相干攻击是安全的。该方案的优点在于利用W态作为信息载体,较GHZ态而言,损耗要小得多,并且不需要在量子信道中传输载有秘密消息的量子比特。     

无线通信领域中空时编码技术

多天线系统是第三代甚至未来的第四代无线移动通信中极具前途的一种技术，本文在论述了无线移动通信中分集尤其发射分集技术必要性的基础上，详细论述了将发射分集与编码相结合而产生的空时编码技术，空时码分为空时格码和空时块码，然后就其性能准则和译码准则进行论述；并讨论一种属于空时块码且不需要信道信息的酉空时码及其编译码准则。文章最后给出空时码研究的最新动态及目前需要解决的问题。