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...     

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.     

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.     

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.     

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.     

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。     

Rake-MMSE-equalizer performance for UWB

The performance of a joint rake and minimum mean square error (MMSE) equalizer receiver for high data rate ultra-wideband communications is studied in this paper. The proposed receiver combats inter-symbol interference by taking advantage of the rake and equalizer structure. The receiver performance is investigated using a semianalytical approach and Monte-Carlo simulation. The effects of the number of rake fingers and equalizer taps on the error performance are examined.     

用于板条激光器均匀面照明的三角形聚光器

用一个二维光线追迹程序,计算了三角形聚光器各几何参数对聚光效率及均匀性的影响,给出了适用于固体板条激光介质均匀面照明的结构参数。计算结果与实验基本一致。     

Broadband compact horn feed for prime-focus reflectors

A compact flare angle controlled corrugated horn antenna with a 60° half beamwidth is optimised by using a moment method for bodies of revolution. The horn has corrugations with simple rectangular cross-sections and is excited by a smooth wall circular waveguide. The resulting 15 dB beamwidth varies by <18% and the crosspolar sidelobe levels are more than 26 dB below the mainlobe, both over a 1.8:1 bandwidth. All results are confirmed by measurements. The horn is suited for broadband feeding of e.g. prime-focus reflectors in radioastronomy applications     

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.     

Power-efficient switching-based CMOS UWB transmitters for UWB communications and Radar systems

This paper presents a new carrier-based ultra-wideband (UWB) transmitter architecture. The new UWB transmitter implements a double-stage switching to enhance RF-power efficiency, reduce dc-power consumption, and increase switching speed and isolation, while reducing circuit complexity. In addition, this paper also demonstrates a new carrier-based UWB transmitting module implemented using a 0.18-/spl mu/m CMOS integrated pulse generator-switch chip. The design of a UWB sub-nanosecond-switching 0.18-/spl mu/m CMOS single-pole single-throw (SPST) switch, operating from 0.45 MHz to 15 GHz, is discussed. The design of a 0.18-/spl mu/m CMOS tunable impulse generator is also presented. The edge-compression phenomenon of the impulse signal controlling the SPST switch, which makes the generated UWB signal narrower than the impulse, is described. Measurement results show that the generated UWB signal can vary from 2 V peak-to-peak with 3-dB 4-ns pulsewidth to 1 V with 0.5 ns, covering 10-dB signal bandwidths from 0.5 to 4 GHz, respectively. The generated UWB signal can be tuned to cover the entire UWB frequency range of 3.1-10.6 GHz. The sidelobe suppression in the measured spectrums is more than 15 dB. The entire CMOS module works under a 1.8-V supply voltage and consumes less than 1 mA of dc current. The proposed carrier-based UWB transmitter and the demonstrated module provide an attractive means for UWB signal generation for both UWB communications and radar applications.     

Related-Key Security for Pseudorandom Functions Beyond the Linear Barrier

Related-key attacks (RKAs) concern the security of cryptographic primitives in the situation where the key can be manipulated by the adversary. In the RKA setting, the adversary’s power is expressed through the class of related-key deriving (\(\mathrm {RKD}\)) functions which the adversary is restricted to using when modifying keys. Bellare and Kohno (EUROCRYPT 2003, volume 2656 of LNCS, Springer, Heidelberg, pp 491–506, 2003) first formalized RKAs and pinpointed the foundational problem of constructing RKA-secure pseudorandom functions (RKA-PRFs). To date there are few constructions for RKA-PRFs under standard assumptions, and it is a major open problem to construct RKA-PRFs for larger classes of \(\mathrm {RKD}\) functions. We make significant progress on this problem. We first show how to repair the framework for constructing RKA-PRF by Bellare and Cash (CRYPTO 2010, volume 6223 of LNCS, Springer, Heidelberg, pp 666–684, 2010) and extend it to handle the more challenging case of classes of \(\mathrm {RKD}\) functions that contain claws. We apply this extension to show that a variant of the Naor–Reingold function already considered by Bellare and Cash is an RKA-PRF for a class of affine \(\mathrm {RKD}\) functions under the Decisional Diffie–Hellman (DDH) assumption, albeit with a blowup that is exponential in the PRF input size. We then develop a second extension of the Bellare–Cash framework and use it to show that the same Naor–Reingold variant is actually an RKA-PRF for a class of degree d polynomial \(\mathrm {RKD}\) functions under the stronger decisional d-Diffie–Hellman inversion assumption. As a significant technical contribution, our proof of this result avoids the exponential-time security reduction that was inherent in the work of Bellare and Cash and in our first result. In particular, by setting \(d = 1\) (affine functions), we obtain a construction of RKA-secure PRF for affine relation based on the polynomial hardness of DDH.