PSD空间定位的非线性误差补偿模型及归一化

PSD是一种高分辨率、实时性好的光电位置敏感器件,因而具有广泛应用的前景.但在光照度变化条件下,输出信号存在非线性飘移,因而影响了作为位置检测传感器的检测精度,尤其在3D测量时适用性受到了限制.针对这个问题,提出了一种PSD位置传感器的非线性误差补偿方法.该方法针对目标的空间距离变化所产生的PSD输出非线性飘移,采用归一化模型进行误差修正,很大程度上改进了PSD的输出一致性,使基于PSD的3D测量系统性能得以提高.

一种新型柔索驱动并联机器人的模型样机

提出一种新型并联机器人机构 ,利用张紧柔索驱动该并联机器人·通过运动学和动力学分析、工作空间分析、轨迹规划、误差分析 ,设计并制作了模型样机本体、驱动与控制模块 ,开发了机器人语言 ,控制模型样机完成指定动作·实验结果表明 ,这种新型并联机器人是可行的 ,适用于轻型机床等设备·该机器人在某一速度范围内工作时 ,会产生较明显的振动 ,并伴有噪声 ,因此要提高机器人的性能还必须设法抑制其振动

新型4自由度并联机器人位姿误差分析

将一种新型四自由度并联机器人等效为由串联机构构成的空间闭环机构 ,运用 Denavit- Hartenberg方法提出了运动平台位姿误差的一种分析算法。利用这个算法可以分析各种构件加工、安装误差对运动平台位姿精度的影响。进行了数值仿真验证了算法的正确性。最后分析出对位姿精度影响较大的因素 ,通过重视这些因素可提高实际机构的操作精度

基于信道估计的RS纠错编码改进算法的设计与实现

提出了一种基于信道估计的RS纠错编码改进算法,该算法可以自适应地根据外界条件和环境对传输信道的干扰变化实时地调节编码系统的数据冗余量。仿真与完整的分析结果证实了该改进算法有效地改善了RS编码算法的传输效率;并且通过实际应用表明:良好的性能,高容错性适应于该通信系统的多种传输信道,具有很强的实用性。

基于模型的立体视觉的优化方法

针对 3D视觉检测中最典型的误差源图像中像素的量化误差 ,在已知模型的条件下 ,对双目立体视觉提出一种模型。利用该优化模型及改进的约束最小二乘法对未知模型的立体视觉解法做一些改进 ,可以明显减小系统的误差。仿真结果表明 ,与未知模型的立体视觉方法相比 ,在同样的量化误差条件下 ,该方法可将系统误差减小 50 %以上。

ROMA: Reliable Overlay Multicast with Loosely Coupled TCP Connections

We consider the problem of architecting a reliable content delivery system across an overlay network using TCP connections as the transport primitive. We first argue that natural designs based on store-and-forward principles that tightly couple TCP connections at intermediate end-systems impose fundamental performance limitations, such as dragging down all transfer rates in the system to the rate of the slowest receiver. In contrast, the ROMA architecture we propose incorporates the use of loosely coupled TCP connections together with fast forward error correction techniques to deliver a scalable solution that better accommodates a set of heterogeneous receivers. The methods we develop establish chains of TCP connections, whose expected performance we analyze through equation-based methods. We validate our analytical findings and evaluate the performance of our ROMA architecture using a prototype implementation via extensive Internet experimentation across the PlanetLab distributed testbed.

Generating Good Degree Distributions for Sparse Parity Check Codes using Oracles

Fast forward error correction codes are becoming an important component in bulk content delivery. They fit in naturally with multicast scenarios as a way to deal with losses and are now seeing use in peer to peer networks as a basis for distributing load. In particular, new irregular sparse parity check codes have been developed with provable average linear time performance, a significant improvement over previous codes. In this paper, we present a new heuristic for generating codes with similar performance based on observing a server with an oracle for client state. This heuristic is easy to implement and provides further intuition into the need for an irregular heavy tailed distribution.

Reliable Cellular Automata with Self-Organization

In a probabilistic cellular automaton in which all local transitions have positive probability, the problem of keeping a bit of information for more than a constant number of steps is nontrivial, even in an infinite automaton. Still, there is a solution in 2 dimensions, and this solution can be used to construct a simple 3-dimensional discrete-time universal fault-tolerant cellular automaton. This technique does not help much to solve the following problems: remembering a bit of information in 1 dimension; computing in dimensions lower than 3; computing in any dimension with non-synchronized transitions. Our more complex technique organizes the cells in blocks that perform a reliable simulation of a second (generalized) cellular automaton. The cells of the latter automaton are also organized in blocks, simulating even more reliably a third automaton, etc. Since all this (a possibly infinite hierarchy) is organized in "software", it must be under repair all the time from damage caused by errors. A large part of the problem is essentially self-stabilization recovering from a mess of arbitrary-size and content caused by the faults. The present paper constructs an asynchronous one-dimensional fault-tolerant cellular automaton, with the further feature of "self-organization". The latter means that unless a large amount of input information must be given, the initial configuration can be chosen to be periodical with a small period.

Adaptive Reliable Multicast

An increasing number of applications, such as distributed interactive simulation, live auctions, distributed games and collaborative systems, require the network to provide a reliable multicast service. This service enables one sender to reliably transmit data to multiple receivers. Reliability is traditionally achieved by having receivers send negative acknowledgments (NACKs) to request from the sender the retransmission of lost (or missing) data packets. However, this Automatic Repeat reQuest (ARQ) approach results in the well-known NACK implosion problem at the sender. Many reliable multicast protocols have been recently proposed to reduce NACK implosion. But, the message overhead due to NACK requests remains significant. Another approach, based on Forward Error Correction (FEC), requires the sender to encode additional redundant information so that a receiver can independently recover from losses. However, due to the lack of feedback from receivers, it is impossible for the sender to determine how much redundancy is needed. In this paper, we propose a new reliable multicast protocol, called ARM for Adaptive Reliable Multicast. Our protocol integrates ARQ and FEC techniques. The objectives of ARM are (1) reduce the message overhead due to NACK requests, (2) reduce the amount of data transmission, and (3) reduce the time it takes for all receivers to receive the data intact (without loss). During data transmission, the sender periodically informs the receivers of the number of packets that are yet to be transmitted. Based on this information, each receiver predicts whether this amount is enough to recover its losses. Only if it is not enough, that the receiver requests the sender to encode additional redundant packets. Using ns simulations, we show the superiority of our hybrid ARQ-FEC protocol over the well-known Scalable Reliable Multicast (SRM) protocol.

Coherent wavelength division multiplexing: a novel transmission format for high spectral density optical communication networks

In this thesis a novel transmission format, named Coherent Wavelength Division Multiplexing (CoWDM) for use in high information spectral density optical communication networks is proposed and studied. In chapter I a historical view of fibre optic communication systems as well as an overview of state of the art technology is presented to provide an introduction to the subject area. We see that, in general the aim of modern optical communication system designers is to provide high bandwidth services while reducing the overall cost per transmitted bit of information. In the remainder of the thesis a range of investigations, both of a theoretical and experimental nature are carried out using the CoWDM transmission format. These investigations are designed to consider features of CoWDM such as its dispersion tolerance, compatibility with forward error correction and suitability for use in currently installed long haul networks amongst others. A high bit rate optical test bed constructed at the Tyndall National Institute facilitated most of the experimental work outlined in this thesis and a collaboration with France Telecom enabled long haul transmission experiments using the CoWDM format to be carried out. An amount of research was also carried out on ancillary topics such as optical comb generation, forward error correction and phase stabilisation techniques. The aim of these investigations is to verify the suitability of CoWDM as a cost effective solution for use in both current and future high bit rate optical communication networks

ALD: adaptive layer distribution for scalable video

Bandwidth constriction and datagram loss are prominent issues that affect the perceived quality of streaming video over lossy networks, such as wireless. The use of layered video coding seems attractive as a means to alleviate these issues, but its adoption has been held back in large part by the inherent priority assigned to the critical lower layers and the consequences for quality that result from their loss. The proposed use of forward error correction (FEC) as a solution only further burdens the bandwidth availability and can negate the perceived benefits of increased stream quality. In this paper, we propose Adaptive Layer Distribution (ALD) as a novel scalable media delivery technique that optimises the tradeoff between the streaming bandwidth and error resiliency. ALD is based on the principle of layer distribution, in which the critical stream data is spread amongst all datagrams thus lessening the impact on quality due to network losses. Additionally, ALD provides a parameterised mechanism for dynamic adaptation of the scalable video, while providing increased resilience to the highest quality layers. Our experimental results show that ALD improves the perceived quality and also reduces the bandwidth demand by up to 36% in comparison to the well-known Multiple Description Coding (MDC) technique.

Equilibrium structure of the hydrogen bonded dimer H2O ⋯ HF

The equilibrium structure of the hydrogen bonded complex H2O HF has been calculated ab initio using the CCSD(T) method with basis sets up to sextuple- quality with diffuse functions and taking into account the basis set superposition error correction. The calculations carried out confirm the importance of diffuse functions and of counterpoise correction to obtain an accurate geometry. The most important point is that the basis set convergence is extremely slow and, for this reason an accurate ab initio structure requires a very large basis set. Nevertheless, the ab initio structure is significantly different from the experimental r0 and rm structures. Analysis of the basis set convergence and of the approximations used for the determination of the experimental structures indicates that the ab initio structure is expected to be more reliable.

Low frequency rTMS effects on sensorimotor synchronization

Previous studies using low frequency (1 Hz) rTMS over the motor and premotor cortex have examined repetitive movements, but focused either on motor aspects of performance such as movement speed, or on variability of the produced intervals. A novel question is whether TMS affects the synchronization of repetitive movements with an external cue (sensorimotor synchronization). In the present study participants synchronized finger taps with the tones of an auditory metronome. The aim of the study was to examine whether motor and premotor cortical inhibition induced by rTMS affects timing aspects of synchronization performance such as the coupling between the tap and the tone and error correction after a metronome perturbation. Metronome sequences included perturbations corresponding to a change in the duration of a single interval (phase shifts) that were either small and below the threshold for conscious perception (10 ms) or large and perceivable (50 ms). Both premotor and motor cortex stimulation induced inhibition, as reflected in a lengthening of the silent period. Neither motor nor premotor cortex rTMS altered error correction after a phase shift. However, motor cortex stimulation made participants tap closer to the tone, yielding a decrease in tap-tone asynchrony. This provides the first neurophysiological demonstration of a dissociation between error correction and tap-tone asynchrony in sensorimotor synchronization. We discuss the results in terms of current theories of timing and error correction.

International on-line reciprocal peer tutoring to promote modern language development in primary schools

The paper reports data from an on-line peer tutoring project. In the project 78, 9–12-year-old students from Scotland and Catalonia peer tutored each other in English and Spanish via a managed on-line envi- ronment. Significant gains in first language (Catalonian pupils) modern language (Scottish pupils) and attitudes towards modern languages (both Catalonian and Scottish pupils) were reported for the exper- imental group as compared to the control group. Results indicated that pupils tutored each other in using Piagetian techniques of error correction during the project. Error correction provided by tutors to tutees focussed on morph syntaxys, more specifically the correction of verbs. Peer support provided via the on- line environment was predominantly based on the tutor giving the right answer to the tutee. High rates of impact on tutee corrected messages were observed. The implications for peer tutoring initiative taking place via on-line environments are discussed. Implications for policy and practice are explored

Energy-Aware Rate and Description Allocation Optimized Video Streaming for Mobile D2D Communications

The proliferation problem of video streaming applications and mobile devices has prompted wireless network operators to put more efforts into improving quality of experience (QoE) while saving resources that are needed for high transmission rate and large size of video streaming. To deal with this problem, we propose an energy-aware rate and description allocation optimization method for video streaming in cellular network assisted device-to-device (D2D) communications. In particular, we allocate the optimal bit rate to each layer of video segments and packetize the segments into multiple descriptions with embedded forward error correction (FEC) for realtime streaming without retransmission. Simultaneously, the optimal number of descriptions is allocated to each D2D helper for transmission. The two allocation processes are done according to the access rate of segments, channel state information (CSI) of D2D requester, and remaining energy of helpers, to gain the highest optimization performance. Simulation results demonstrate that our proposed method (named OPT) significantly enhances the performance of video streaming in terms of high QoE and energy saving.