Minimize Error Propagation Research Articles

Registration of surfaces minimizing error propagation for a one-shot multi-slit hand-held scanner

We propose an algorithm for the on-line automatic registration of multiple 3D surfaces acquired in a sequence by a new hand-held laser scanner. The laser emitter is coupled with an optical lens that spreads the light forming 19 parallel slits that are projected to the scene and acquired with subpixel accuracy by a camera. Splines are used to interpolate the acquired profiles to increase the sample of points and Delaunay triangulation is used to obtain the normal vectors at every point. A point-to-plane pair-wise registration method is proposed to align the surfaces in pairs while they are acquired, conforming paths and eventually cycles that are minimized once detected. The algorithm is specially designed for on-line applications and can be classified as a closing-the-loop technique, where there are not that many competing methods, though it has been compared to the literature. Experiments providing qualitative and quantitative evaluation are shown by means of synthetic and real data and we demonstrated the reliability of our technique.

화상통신에서의 오류전파 제어를 위한 보조모션벡터 코딩 기법

인터넷을 통해 동영상을 전송할 때, 네트워크의 상태에 따라 패킷 손실이 발생할 수 있다. 패킷 손실이 발생하면 해당 프레임 뿐 아니라, 그 프레임을 참조하는 다른 프레임의 화질에도 영향을 미치는 오류전파가 발생한다. 본 논문에서는 전송 중 패킷 손실로 인한 오류전파를 최소화하기 위한 부호화 기법인 AMV(Auxiliary Motion Vector)를 제안한다. AMV 기법에서 부호기는 한 개의 매크로블록을 압축하기 위해 여러 프레임과의 움직임 예측을 수행한 후, 상위 두 개의 매칭블록을 선택한다. 두 블록 중 압축 대상 매크로블록과 더 유사한 블록을 움직임 보상에 이용하며 이 블록을 참조블록 또는 기본블록이라 한다. 나머지 블록을 보조블록이라 하며 참조블록이 손실된 경우 복호기가 참조블록의 대체용으로 이용한다. 보조블록의 정보는 압축된 매크로블록의 헤더에 블록의 모션벡터와 프레임 번호를 삽입함으로써 전송된다. 이 기법은 다른 기법에 비해 압축에 이용되는 참조블록의 수를 최소화하고 보조블록을 이용하여 오류를 요구함으로써 오류전파가 발생하는 범위와 그 강도를 줄이는 장점이 있다. 제안된 기법의 코덱을 구현하기 위해 H.263 표준 소스를 수정하였으며, 다양한 패킷 손실율의 트레이스를 생성하기 위해 시뮬레이션 툴인 NS-2를 이용하였다. 실험 결과 제안된 기법은 전체적으로 H.253 표준에 비하여 높은 성능을 나타냈으며 특히 화면의 변화가 적은 경우 패킷 손실율이 높을수록, 변화가 심한 경우 패킷 손실율이 낮을수록 높은 성능을 나타내었다. In this paper, we propose a video sequence coding scheme called AMV (Auxiliary Motion Vector) to minimize error propagation caused by transmission errors over the Internet. Unlike the conventional coding schemes the AMY coder, for a macroblock in a frame, selects two best matching blocks among several preceding frames. The best matching block, called a primary block, is used for motion compensation of the destination macroblock. The other block, called an auxiliary block, replaces the primary block in case of its loss at the decoder. When a primary block is corrupted or lost during transmission, the decoder can efficiently and simply suppress error propagation to the subsequent frames by replacing the block with an auxiliary block. This scheme has an advantage of reducing both the number and the impact of error propagations. We implemented the proposed coder by modifying H.263 standard coding and evaluated the performance of our proposed scheme in the simulation. The simulation results show that AMV coder is more efficient than the H.263 baseline coder at the high packet loss rate.

Techniques for minimizing error propagation in decision feedback detectors for recording channels

Decision feedback equalization (DFE) is a low-cost approach for signal detection in magnetic recording channels. However it suffers from the phenomenon of error propagation (EP). In this paper two approaches are proposed for minimizing EP in DFE. The first approach imposes appropriate constraints on the feedback equalizer. The second approach uses simple threshold techniques to detect the presence of decision errors and to either correct these errors or minimize the possibility of further errors. Computer simulations show that the proposed techniques reduce EP very significantly. Theoretical analyses of the threshold techniques are presented to quantify the associated false and correct detection probabilities. By combining the analysis with an existing EP simulation method, a fast simulation procedure is derived for estimating EP and bit error rate (BER).

Joint coding and decision feedback equalization for broadband wireless channels

This paper introduces a new approach for joint convolutional coding and decision feedback equalization (DPE). To minimize error propagation, the DFE uses a combination of soft decisions and delayed tentative decisions to cancel intersymbol interference (ISI). Soft decisions are obtained by passing the DFE output through a (soft) nonlinear device. This simple method is shown to perform almost as well as an optimum soft feedback approach on wireless channels with diversity. Tentative decisions from the Viterbi decoder are used to cancel ISI due to multipath with large delays, thus remedying the increasing effect of error propagation in channels with large delay spreads. We consider the use of this soft/delayed feedback DFE (S/D-DFE) technique in broadband wireless channels (with delay spreads up to several tens of the symbol period) typical in high-bitrate mobile data applications. Simulation results indicate that the proposed joint coding and S/D-DFE technique performs to within 1-2 dB [in required signal-to-noise ratio (SNR)] of an ideal coded DFE without error propagation. When combined with antenna diversity and a reduced-complexity DFE concept with adaptive feedforward tap assignment, it provides high packet throughput against Rayleigh fading, severe delay spreads, and high Doppler rates.

Optimal synthesis of robot manipulators based on global kinematic parameters

A method to represent and measure the global manipulability of manipulators is presented. The method is based on a new concept, referred to as the global velocity ellipsoid, which represents the global motion manipulability or the velocity transmission characteristics of a manipulator. The global velocity ellipsoid is obtained by considering a weighted distribution of the end-effector position over the workspace of the manipulator. Parameters representing the global isotropy and the global magnitude of the velocity transmission of manipulators are used for analyzing and optimizing the kinematic structure of manipulators. The extension of the concept to force transmission characteristics and its utilization for minimizing error propagation and enhancing accuracy, task placement and planning are discussed. Several examples are presented.

A novel approach to the solution of indirect measurement problems with minimal error propagation

A general solution method for indirect-measurement problems is developed, and implemented in a FORTRAN-IV program. A comparison with the conventional approach shows that the accuracy improvements gained can be very substantial. Use of the method for testing the validity of measurement set-ups, and for improving them is discussed. Attention is also paid to the theoretical implications of the approach. An analysis of conventional solution techniques is given which illustrates the basic weakness associated with these methods. A comparison is made with the theory of stochastic estimation and with the formal theory of measurement, and a fundamental problem in the formulation of the latter is presented.

Estimation of Tissue Blood Perfusion Rate from Diffusible Indicator Measurements: A Sensitivity Analysis

Recording the washout of indicator (for example, heat, radio-labeled dissolved gas, etc.) transiently introduced into tissue allows the estimation of tissue blood perfusion rate. Analysis of the washout data requires a material balance which appropriately accounts for all transport mechanisms and sources and sinks of the given indicator. From that balance one may perform a sensitivity analysis which specifies the susceptibility of the perfusion estimate to experimental errors in any of the pertinent parameters and variables. The sensitivity analysis is based on the normalized partial derivatives of tissue indicator concentration with respect to the experimental variables. The results indicate that the estimation of the tissue blood perfusion rate is highly sensitive to errors in the concentration of the diffusible indicator which dominate, by two orders of magnitude or more, the errors attributed to other parameters. For typical experimental conditions, the errors in the perfusion estimate due to the various parameters are shown to vary considerably, according to the sensor position and time of measurement. Based on this type of analysis, one may specify optimal temporal and spatial domains for the parameter estimation in order to minimize error propagation. The optimal time domains are shown to differ from those used in typical indicator washout analyses for estimating tissue perfusion rate.