室内信道环境下UWB精确测距研究

研究了IEEE 802.15.4a室内信道环境下UWB(ultra wideband)信号的精确测距能力。提出了一种改进的基于区间搜索和门限比较的TOA(time of arrival)估计算法。基于对CM1和CM2信道实现的部分参数的统计分析,建立了TOA估计误差的概率模型,并由此给出了通过将误差概率控制到最低的算法门限设置方案。通过仿真考察了不同信噪比下测距结果的平均绝对误差。结果表明,UWB在室内信道条件下要获得厘米级的测距精度,接收信号须保证足够高的信噪比,但信噪比提高到一定程度后测距性能并不会进一步提升,此结论对于设计满足一定精度需求的定位算法以及实际测距中控制信号的传输功率具有一定的指导意义。     

Detection of UWB ranging measurement quality for collaborative indoor positioning

Wireless communication signals have become popular alternatives for indoor positioning and navigation due to lack of navigation satellite signals in such environments. The signal characteristics determine the method used for positioning as well as the positioning accuracy. Ultra-wideband (UWB) signals, with a typical bandwidth of over 1 GHz, overcome multipath problems in complicated environments. Hence, potentially achieves centimetre-level ranging accuracy in open areas. However, signals can be disrupted when placed in environments with obstructions and cause large ranging errors. This paper proposes a ranging measurement quality indicator (RQI) which detects the UWB measurement quality based on the received signal strength pattern. With a detection validity of more than 83%, the RQI is then implemented in a ranging-based collaborative positioning system. The relative constraint of the collaborative network is adjusted adaptively according to the detected RQI. The proposed detection and positioning algorithm improves positioning accuracy by 80% compared to non-adaptive collaborative positioning.     

NLOS error mitigation with information fusion algorithm for UWB ranging systems

This article puts forward a scalar weighting information fusion (IF) smoother with modified biased Kalman filter (BKF)and maximum likelihood estimation (MLE) to mitigate the ranging errors in ultra wid...     

Model of human body influence on UWB ranging error

Based on UWB channel,in which human body occlusion application scenarios,the influence of human body on TOA range error by measurement and analysis of TOA ranging error was studied.The TOA ranging error model caused by single side of human body through building a suitable measuring platform and dealing with test result was established.Then Matlab software simulation was used to verify the accuracy of TOA ranging error in human occlusion application scenarios,and the influence of creeping surface wave on TOA ranging was analyzed.     

Application of power transformation and moments in time based UWB ranging

For ultra-wideband (UWB) ranging, TOA estimation with the energy detection (ED) receiver is to detect the energy sample that contains the first path (FP) signal in dense multipath. Threshold crossing (TC) is used frequently. However, it is difficult to determine the threshold. Some threshold setting methods are based on constant false alarm rate (CFAR) and the chi-squared distribution. However, the distribution is complicated. Moreover, it depends on the degree of freedom (DOF). If the DOF used is wrong, it will degrade the detection performance. The study bypasses the distribution. We first examine the distribution of the output of the ED receiver after power transformation. Based on the new characteristics of the transformed data and approximate distributions, we propose some practical TOA estimation methods. Similarly, the moments of the output of the ED receiver, such as the second or one-third order moments, are also analysed and used. The proposed methods are easy to implement and can achieve about the same ranging performance with methods based on the chi-squared distribution. We provide both theoretical and simulation results to prove their effectiveness.     

一种提高相位测距精度的方法

在激光相位测距中,距离是通过求回波信号的相位信息求得的。由于频谱泄露和栅栏效应,传统的FFT不能精确地计算出频率点的相位值,因此提出使用密集频谱细化技术和频谱校正技术对回波信号的频谱进行校正。实验结果表明:基于复解析带通滤波器的复调制谱细化算法所需的运算量少,计算速度快,同时能够提高相位测量精度;频谱校正算法中相位差校正算法是一种精确的校正方式,校正精度很高;频谱细化和频谱校正技术大大提高了频谱分辨率。在工程应用中,本文方法运用于激光相位测距中能大幅度提高频域数字测相的精度。     

High precision ranging with IR‐UWB: a compressed sensing approach

Ranging has been regarded as one of the fundamental enabling technologies for a multitude of applications that require high accurate position information, such as automated navigation, vehicle platooning, asset management, etc. Among various ranging techniques, impulse‐radio ultra‐wideband is one of the most competitive technologies for high‐precision ranging, because of its capability of achieving centimeter‐level ranging accuracy, even for dense urban, indoor or cave like environments. However, two main challenges arise when fully exploiting the ranging capability of impulse‐radio ultra‐wideband: (i) the extremely high sampling rate to acquire the received multipath signal, and (ii) the optimal thresholding strategy to differentiate the first path. To efficiently tackle those challenges, in this work, we propose a ranging approach under the compressed sensing framework. Specifically, the received ranging signal is acquired by low‐rate compressed sampling through parallel random projections. Then, an algorithm named matching‐pursuit search‐back is proposed to detect the first arrival path, which integrates a backward iterative search and thresholding process starting from the peak path. The detection threshold is dynamically adjusted in each iteration to asymptotically minimize the averaged detection errors over false alarm and missed detection. Extensive simulations and experiments with field data are provided to demonstrate that the proposed approach can achieve high‐precision ranging with far fewer samples compared with the traditional Nyquist‐sampling based ones. Copyright © 2016 John Wiley & Sons, Ltd.     

空间碎片精密测角和测距仿真数据定轨性能分析

目前空间碎片精密跟踪数据可以通过光学测角和激光测距两种手段获取。文中旨在通过大量的仿真实验来分析上述两种手段获取的数据对碎片定轨及预报性能的影响,以期根据各自的特点更好地利用稀缺的数据资源。首先利用了2015年1月Starlette和Larets卫星CPF精密预报轨道作为参考轨道,仿真生成基于国内区域内4个观测站精度1的测角数据和精度1 m的测距数据,然后,利用仿真数据生成单站和双站算例并进行定轨,得到完整弧段及部分弧段的测角、测距数据定轨预报结果。结果表明:在上述观测数据精度基础上,测角数据较测距数据在定轨中的表现更加稳定,将完整通过弧段缩短至90 s时,约75%的角度定轨算例的短期(1~2天)预报轨道仍能够满足20精度要求。实验结果同时表明:单站、双站定轨预报误差分布相似。     

截断伪随机序列的统计特性

讨论了直接序列扩频(DSSS)系统中常用的伪随机码的统计特性。分析了截断m序列、Gold序列的统计性能。m序列、Gold序列在截断使用时,它们的统计特性与原序列的周期统计特性可比拟。     

Fast and accurate automatic registration for MR-guided procedures using active microcoils

A fast, robust, accurate, and automatic registration technique based on magnetic resonance (MR) active microcoils (active markers) for registration of tracked medical devices to preprocedural MR-images is presented. This allows for a straight-forward integration of position measurement systems into clinical procedures. The presented method is useful for guidance purposes in clinical applications with high demands on accuracy and ease-of-use (e.g., neurosurgical or orthopedic applications). The determination of the positions of the active markers is integrated into the preparation phase of the actual MR imaging scan. The technique features a generic interface using DICOM standards for communication with navigation workstations linked to an MR system. The position of the active markers is fixed with respect to a reference system of an optical positioning measurement system (OPMS) and thus the coregistration of the MR system and the OPMS is established. In a phantom study, a mean overall targeting accuracy of 0.9+/-0.1 mm was achieved and compared favorably to results obtained from manual registration tests (1.8+/-0.3 mm) carried out in parallel. For a test person trained for both registration methods, workflow improvements of 3-6 min per registration step were found. The need for manual interaction is entirely eliminated thus avoiding user-bias, which is advantageous for the usage in clinical routine. The method improves the ease-of-use of tracking equipment during stereotactic guidance. The method is finally demonstrated in a volunteer study using a model of a Mayfield skull clamp with integrated active and optical reference markers.     

Design considerations for shaped-beam reflectors

A modified procedure is proposed for the design of shaped-beam reflectors in general. The procedure involves explicitly the size of the reflector as a parameter and can thus be used to check quickly the minimum size of a reflector needed for a given shaped beam. Experimental results are given for a reflector designed on this basis.     

Bragg reflectors for cylindrical waves

A transfer-matrix method has been developed for cylindrical waves. Expressions are obtained for reflection and transmission coefficients of cylindrical light waves by an isolated cylindrical boundary that separates two media and a cylindrical layered medium. A construction is proposed for optimized “Bragg” reflectors for cylindrical waves and the properties of these reflectors are investigated. Fiz. Tekh. Poluprovodn. 33, 174–179 (February 1999)     

Aperture efficiency for paraboloidal reflectors

The definition and formulas for cross polarization, phase error, and illumination efficiency given by Ludwig and Thomas are shown to not always account for the correct cross polarization and phase error loss. New definitions and formulas are proposed that give a better separation of the losses associated with cross-polarized radiation, phase errors, and nonuniform aperture illumination.     

Pseudorandom Coding for Improved Antenna Range Measurements

The autocorrelation function for pseudorandom binary codes is such that these codes are ideal for suppressing unwanted reflections on antenna ranges. The method presented here depends on amplitude modulating the transmitted signal with a maximum-length linear recurring modulo-two sequence (PN code) and correlating it at the receiver with a delayed version of the code. In this way reflections whose path transit times are greater than 1 bit time from the direct path transmission time are reduced in amplitude by a factor inversely proportional to the length of the code word. Also presented is a simple means for generating the maximum-length shift-register codes using delay lines and mixers that makes this method especially practical for most antenna range applications.     

Resonant reflectors for free electron masers

A new type of a waveguide reflector is discussed. Its operating principle is based on the effect of resonant reflection of a wave from a cavity when there is coupling between the wave and an eigenmode of the cavity. The resonant reflectors are very attractive for the use in microwave systems of free electron masers due to their high reflection coefficients and narrow frequency bands at comparatively short lengths. Results of calculations and measurements of some resonant reflectors and a microwave system for KA-band cyclotron autoresonance masers are presented.     

Beam-scanning primary feed for parabolic reflectors

A system is described which achieves wide-angle beam scanning from a parabolic reflector antenna by movement of an adaptive primary-feed system about a defined locus. The feed system performs a sampled spatial Fourier transformation of the focal-plane field in order to obtain a uniform power distribution prior to phase compensation and summation. Scanning of ±15 beamwidths with less than 0.5dB loss in gain and negligible beam distortion has been demonstrated experimentally.     

A Gregorian corrector for spherical reflectors

The inherent spherical aberration of a spherical reflector antenna is corrected by using an auxiliary Gregorian reflector feed system that rotates about the center of curvature of the reflector. Tests at bothX- andK-band frequencies demonstrate feasibility of the design for wide-angle scanning.     

Modified diffraction coefficients for focusing reflectors

A modification to the halfplane diffraction coefficients is given for a plane wave incident on a curved screen. The result is used to calculate the near field of a parabolic reflector under plane-wave illumination. Comparison with the physical-optics method shows excellent agreement.     

EPON系统测距技术的研究

测距技术是EPON系统的关键技术之一，其测量结果的准确度直接影响着上行链路动态带宽分配算法的效率乃至整个网络性能。分析了EPON系统中测距技术的必要性，介绍了基于多点控制协议的时间戳测距的基本原理，最后讨论了测距的延时补偿问题。     

Multiwavelength grating reflectors for widely tunable laser

We propose a new reflector approach in order to get the reflectivity comb needed in widely tunable lasers. This reflector is realized by holographic exposure of superimposed multiple Bragg gratings. It provides efficient reflectivity with short guide sections (150 /spl mu/m) leading to improved static laser characteristics. This reflector has been successfully included in 20-nm tuning DBR lasers.