New searching flow scheme for incremental backprojection algorithm

A new two-dimensional (2D) searching flow scheme is proposed for the incremental backprojection algorithm (see IEEE Trans. Med. Imaging, vol.9, p.207, 1990). In this scheme, the searching direction in a beam is determined only by the distance of the current pixel to the corresponding ray and no pixels outside the beam are involved in the procedure. The proposed scheme possesses a simple structure. Implementations on an AST-386 computer for the incremental backprojection algorithm by using this new scheme show that the processing time can be reduced by a factor of approximately 1.4 compared with the original scheme.<>     

Incremental algorithm-a new fast backprojection scheme for parallel beam geometries

A fast backprojection scheme for parallel beam geometries is proposed. Known as the incremental algorithm, it performs backprojection on a ray-by-ray (beam-by-beam) basis rather than the pixel-by-pixel backprojection in the conventional algorithm. By restructuring a conventional backprojection algorithm, the interdependency of pixel computations (position and value) is transformed to a set of incremental relations for a beam, where a beam is a set of pixels enclosed by two adjacent rays in 2-D computed tomography (CT), and a set of voxels enclosed by four adjacent rays in 3-D CT. To minimize the overhead of searching for the next pixels, a searching flow technique has been developed to implement the first-order and second-order incremental relations for 2-D and 3-D CTs, respectively. The values of all the pixels in each beam (except the first pixel) are computed with additions only, the key idea of the proposed backprojection scheme. The incremental algorithm has been implemented on two different machines and compared to B.F. Shepp and L.A. Logan's (1974) algorithm. The present implementation results show the superiority of this approach over the conventional algorithm.     

Incremental backprojection algorithm: modification of the searching flow scheme and utilization of the relationship among projection views

A two-dimensional (2-D) search flow scheme is proposed for the incremental backprojection algorithm. In this scheme, the searching direction in a beam is determined only by the distance from the current pixel to the corresponding ray; no pixels outside the beam are involved in the procedure. In addition, the geometrical relationships between the image grids and the projection rays in different views are fully exploited to further reduce the search operations. It is found that backprojection of four views can be performed at the same time, and the search operation is only required for one of them if the number of views is even. Thus, backprojection is accomplished on a quartet-by-quartet of views basis as well as on beam-by-beam basis. These approaches not only minimize the number of search operations but also possess a simple algorithm structure. Implementation results obtained with an AST-386 computer for the incremental backprojection algorithm using this search flow scheme and the relationship among projection views show that the processing time can be reduced by a factor of about 2.     

基于透镜天线阵的毫米波系统波束选择研究

透镜天线阵列下毫米波大规模多输入多输出(MIMO)系统通过波束选择可以大大减少所需的射频链数目,解决系统硬件成本和能耗过高的问题,然而,波束选择需要基站端获取准确的信道状态信息。对此,文章首先利用波束空间的结构特性,采用基于支持检测(SD)的信道估计方案,以较低的导频开销和计算复杂度对大尺寸信道进行更加可靠的估计;其次受仿生学中蚁群优化(ACO)算法的启发,文章提出了一种基于SD估计信道的ACO波束选择方案,该方案既能有效地避免用户间波束的干扰,又能最大限度地提高系统和速率;最后,仿真结果表明,该方案能够得到计算复杂度显著降低的近优解,在提高系统和速率方面优于现有方案。     

面向无人机毫米波高效波束搜索的码本优化设计

针对无人机(UAV)动态环境下,波束无法实时匹配这一问题,结合毫米波数字-模拟混合波束形成系统,提出采用一种低复杂度的码本设计方法,以提高波束搜索效率。该方法首先建立了分层波束搜索模型并提出以扇形波束作为训练波束;其次将扇形波束的阵列响应改写为傅里叶级数形式,并利用傅里叶反变换得到扇形波束的理想数字码本;最后通过几何贪婪(Greedy Geometric, GG) 算法设计数字基带预编码器和射频预编码器,得到了具有快速搜索能力的优化波束。仿真结果表明,该码本优化方法具有较低的复杂度,有效地提高了波束搜索效率,满足了无人机实时波束匹配需求。     

IEEE802.11切换中一种快速主动扫频算法

提出了一种IEEE802.11切换过程中的快速主动扫频算法。首先STA从扩展了位置信息的邻居AP图中选择被扫频的AP,然后采用单播方式完成扫频。改进算法减轻了由多余信道扫频、等待时延和信道冲突所产生的时延。仿真分析表明,改进算法确保切换完成,并明显地减小了扫频时延。     

An efficient delay constrained scheduling scheme for IEEE 802.16 networks

In this paper, we propose a simple yet efficient delay-constrained scheduling scheme for IEEE 802.16 networks. The proposed scheduling scheme not only can satisfy delay constraints of different service types by manipulating a simple operation parameter but also can achieve a good fairness performance. An analytical model is developed to evaluate the performance in terms of inter-service time, average queue length, and mean waiting time, and is verified through extensive simulations. Furthermore, an implementation procedure of the proposed scheme is given, which reflects the scheme’s good features of the fast re-configurability and adaptability.     

一种基于DBF的反辐射导引头快速测向技术

为了提高反辐射导引头角度搜索的速度,文中提出了一种基于数字波束形成的快速测向技术。该技术基于折半查找的思想,将角度搜索问题转换为利用不同宽度的数字波束进行空间目标角度的折半查找问题。研究了该方法的基本原理,分析了其搜索速度和运算量。仿真结果显示,该方法在保证应有的测角精度与角度分辨力的条件下,解决了传统数字波束形成时侦测时间较长,且效率低的问题。     

Step-Wisely Refinement Based Beam Searching Scheme for 60 GHz Communications

In the emerging 60 GHz millimeter-wave communications, the beam-forming technique has been widely recommended to efficiently compensate the significant path-loss in such bands. Unfortunately, the complexity of beam searching procedure, which is used to find the optimal beam-pair from a prescribed codebook, may generally tend to be unaffordable with the increasing of antenna elements. By formulating the beam-searching as a numerical optimization problem and properly exploring the beam characteristics generated by different array element numbers, the article proposed a fast beam searching algorithm. Compared with the existing schemes in current standards, our algorithm can significantly reduce the preamble transmissions accompanying energy consumption during beam searching process. Numerical simulation results further validate the superiority of the presented algorithm.     

一种层次型的曲线拐点搜索算法

本文提出了一种快速准确的提取曲线拐点的算法。算法的总体结构是层次型的，它分级逐次淘汰伪拐点，而对每一级的处理又是顺序的逐点考察。因此，这种层次型的结构可抑制误差。实验表明，该算法不仅处理时间短，而且能保持原始曲线的总体形状，搜索出的拐点冗余度小，因而要求的存储容量小。     

求解带度约束多播路由问题的启发式遗传算法

为了能够有效求解带有度约束的多播路由模型，融合启发式算法与遗传算法，利用染色体作为启发信息，设计了一种求解该模型的混合遗传算法。该算法不但避免了直接对树形数据结构编码所带来的困难，而且具有快速收敛的特点和全局寻优的能力。最后，大量的数字仿真从实践上支持了该算法的有效性。     

一种恒定束宽的宽带自适应波束形成算法

宽带波束形成是相控阵雷达数字信号处理的难点。针对目前宽带波束形成只能满足单一恒定束宽或自适应情况,为兼具两种优势使雷达工作状态更佳,文中基于最小二乘算法提出了一种自适应波束形成方法,该方法通过获得自适应参考波束图,确定波束图恒定范围根据最小二乘算法求取其他频点权值,并进行宽带波束形成。该方法不仅能保证恒定束宽,而且可实现自适应零陷控制。仿真实验证明了算法的有效性。     

一种基于IEEE802.11支持QoS自适应调度器模型和算法

这篇文章提出了能够有效支持QoS的IEEE802．11自适应调度器模型。和以往的支持QoS的调度器模型相比，这里根据在主控接入点(MAP：Master Access Point)和用户终端(UT：User Termination)的各自延时需求对满足不同的传输机制的分组流进行自适应调度。这种机制不仅完全兼容当前支持QoS的IEEE802．11MAC协议标准，而且能够有效减少由于实时传输带来的分组延时，增加满足不同信道负载和带宽要求的数据流的吞吐率。实时测试得到的数据基本验证了这个要求。     

60 GHz毫米波通信中一种新的波束搜索算法

采用毫米波进行信号传输,使多天线技术集成实现成为可能,继而可利用阵列天线波束赋形技术。然而,当天线阵元数增多时,将导致最优波束对的搜索算法复杂度急剧增加。该文充分利用不同数目阵元产生的波束特性,提出一种基于划区而治的逐步细化高效搜索算法;通过逐步增加使能天线数目,有效缩小搜索空间,最终实现最优波束对搜索。相比于现有方案,该算法能显著降低搜索过程中信令传输及能量消耗,仿真结果进一步验证了该算法的有效性。     

一种高灵敏度GPS信号快速捕获算法

为了提高GPS软件接收机捕获算法的灵敏度和快速性,提出了一种高灵敏度GPS卫星信号快捕方案。首先对GPS信号进行频率补偿,然后进行相干滤波提高卫星信号的信噪比,从而提高捕获算法的灵敏度。再采用延迟、累积捕获结构寻找输入信号中各颗卫星的C/A码起始点,引入延迟累加器实现各卫星多普勒频移成分的分离、估计,将传统的二维捕获过程简化为两个一维搜索过程,捕获时间仅为传统FFT快捕算法的几十分之一,提高了捕获算法的速度。分别通过实测和GPS数字中频信号发生器仿真生成的GPS数字中频数据对所设计的捕获算法进行了验证,实验结果表明该捕获算法行之有效。     

基于目标优先级的跟踪波束调度方法研究

针对协方差控制的策略不满足雷达跟踪目标的实时性要求,文中采用协方差和目标威胁度联合控制的方法来研究关于相控阵雷达波束调度的问题,建立相控阵雷达波束分配的最优化模型。该模型利用目标的运动状态信息,包括目标距离、目标径向速度、加速度和航向,利用层次分析法确定目标威胁度,然后与目标跟踪协方差相结合进一步确定目标优先级,实现目标动态的搜索加跟踪模式(TAS)的波束调度。将该算法与传统的顺序波束调度方法进行比较,仿真结果表明该算法具有较高的时间利用效率,同时也具有较好跟踪性能。     

适用于H.263(+)的一种运动估计快速搜索算法

介绍了适合H.263的一种改进算法.改进的新三步法(improved NISS),基于NISS的改进方案,结合H.263(+)的高级选项使用时可以大大减少计算量.采用全搜索算法计算量最大,各种快速算法都是以限制搜索步骤或点数来换取计算量的大大减少,同时保证了性能的降低最小.无论运动图像剧烈与否,该方案都提出了克服的方法.实际测试表明改进的这种方法性能上几乎达到了全搜索法(FS)的结果,而时间上只有FS的5%左右.     

基于自适应滑动窗的模糊场景行人快速检测

智能场景监控是公共安全领域研究的热点.然而当前公共场所监控视频大都比较模糊,如何能够在模糊场景下快速检测行人目标是一个亟待解决的问题.通过引入一个自适应尺寸的行人检测窗,以特定策略滑动扫描前景二值图像,并根据一系列行人轮廓判别条件获取行人目标,实现了对模糊监控场景的实时行人检测与人数统计.实验结果表明,与传统算法相比,该算法可以有效快速地检测出指定区域内的行人目标.     

基于樽海鞘群算法的无源时差定位

针对无源时差(TDOA)定位的非线性方程解算问题,论文使用一种名为樽海鞘群算法(SSA)的新的群体智能优化算法。首先,该算法采用一种新的群体更新模型,充分平衡迭代过程中的探索行为与开发行为,在保证搜索的全局性与个体的多样性的同时,改善了其他智能优化算法容易陷入局部极值的问题。其次,该算法控制参数很少,运算速度明显提高。该算法的收敛速度十分稳定,定位精度更高。仿真结果表明,樽海鞘群算法在3维时差定位中能够快速、稳定地收敛至目标位置,对传统粒子群算法(PSO)、改进的线性权重粒子群算法(IPSO)与SSA的定位精度进行比较,SSA精度明显高于PSO与IPSO。     

Game‐based cross‐layer channel allocation with SVC‐encoded multimedia streams in cognitive radio networks

The available unlicensed spectrum is increasingly being used by new wireless technologies, but past measurements show that the licensed spectrum is extremely underutilized. To address this issue, the IEEE 802.22 Working Group is developing a novel wireless air interface standard based on cognitive radios (CRs), i.e. IEEE 802.22 wireless regional area networks (WRANs). Moreover, over the last decade wireless multimedia applications have developed rapidly, raising significant concerns about the quality of service (QoS) of multimedia stream transmissions. In particular, the Joint Video Team (JVT) and ITU‐T Video Coding Experts Group (VCEG) jointly proposed Scalable Video Coding (SVC) as the next‐generation multimedia compression standard. However, the current IEEE 802.22 WRAN draft does not specify QoS mechanisms for SVC‐encoded multimedia stream transmission in CR networks. To resolve this problem, we developed a cross‐layer channel allocation algorithm (CLCAA) and a novel media access control (MAC) protocol to work with the algorithm. The CLCAA adapts to the characteristics of multimedia traffic and variations of wireless channels by determining the weighting of source–destination pair, which is determined by the deadlines of SVC‐encoded multimedia streams, the queuing delay and channel conditions. The CLCAA then allocates transmission opportunities to source–destination pairs based on their weightings and game theory. We also conducted extensive simulations to demonstrate the efficiency of the CLCAA scheme. The simulation results show that the CLCAA scheme not only guarantees QoS for multimedia traffic but also achieves fairness across different streams. Copyright © 2012 John Wiley & Sons, Ltd.