Feedback control strategies for object recognition

We present a paradigm for feedback strategies that find instances of a generic class of objects by improving on established single-pass hypothesis generation and verification approaches. We improve upon the mechanisms of the traditional or classical image processing systems by introducing control strategies at low, intermediate, and high levels of analysis. We produce optimal sets of low-level features to reduce the number of hypotheses generated. The feedback further enables updated sets of features to be extracted so that the target object may be located even in very, noisy data. The use of an interest operator in the feedback directs the search through the hypotheses in an optimal manner, so minimizing the amount of feedback to false alarms. Furthermore, we aim to obtain detailed information about a complex object and not just its location. Thus, following top-down recognition of the object our feedback control directs the search for missing information. The system can extract complex objects in a scale and rotation independent manner where the objects may be partially occluded. The method is illustrated using box shaped objects and noisy IR images of a number of bridges     

Feedback control mechanisms for real-time multipoint video services

While existing research shows that reactive congestion control mechanisms are capable of providing high video quality and channel utilization for point-to-point real-time video, there has been relatively little study of the reactive congestion control of point-to-multipoint video, especially in ATM networks. Problems complicating the provision of multipoint, feedback-based real-time video service include: (1) implosion of feedback returning to the source as the number of multicast destinations increases and (2) variance in the amount of available bandwidth on different branches in the multipoint connection. A new service architecture is proposed for real-time multicast video, and two multipoint feedback mechanisms to support this service are introduced and studied. The mechanisms support a minimum bandwidth guarantee and the best effort support of video traffic exceeding the minimum rate. They both rely on adaptive, multilayered coding at the video source and closed-loop feedback from the network in order to control both the high and low priority video generation rates of the video encoder. Simulation results show that the studied feedback mechanisms provide, at the minimum, a quality of video comparable to a constant bit rate (CBR) connection reserving the same amount of bandwidth. When unutilized network bandwidth becomes available, the mechanisms are capable of exploiting it to dynamically improve video quality beyond the minimum guaranteed level     

基于SVPWM永磁同步电机反馈线性化控制

为了实现对永磁同步电机很好控制的目的,采用反馈线性化的方法,通过求取输出变量的李导数,得到需要的坐标变换和状态反馈变量,设计了控制器。利用MatLab7.6/Simulink做了基于SVPWM的永磁同步电机的反馈线性化控制仿真实验。在加不同大小负载的情况下,验证算法对不同负载速度跟踪的效果,获得了反馈线性化控制对永磁同步电机跟踪控制效果好的结果,得到了反馈线性化控制具有很好的鲁棒稳定性,是控制非线性系统的一个好方法结论。     

Feedback control of the nuclear magnetization state: modeling and control design

Magnetic resonance (MR) images are obtained by observing the fluctuations in nuclear magnetization produced by sequences of RF pulses and applied magnetic field gradients. The design of a pulse sequence is based on the expected response of the nuclear magnetization. Currently, all pulse sequence parameters are loaded into the pulse programmer before the start of the sequence and remain unchanged until the completion of the sequence. A fundamentally different approach is considered, whereby the sequence parameters are adjusted between successive RF excitation pulses. In this manner, the nuclear magnetization is regulated to a desired state by using measurements of the magnetization to adjust the amplitude and duration of the RF pulses. Feedback control of the nuclear magnetization state may be advantageous in certain types of MR experiments, for example those requiring a repeated spin-echo or gated MR image acquisition. As a first step in developing this approach a simple scheme for regulating the angle between the bulk magnetization and the axis applied static magnetic field is presented. The behavior of the closed-loop system is explored using computer simulations.     

Feedback control of a biodynamical model of HIV-1

We describe a continuous differential equation model of the interaction dynamics of HIV-1 and CD4 and CD8 lymphocytes in the human body. We demonstrate several methods of stable control of the HIV-1 population using an external feedback control term that is analogous to the introduction of a therapeutic drug regimen. We also show how the immune system components can be bolstered against the virus through a feedback control approach.     

基于自适应反步跟踪的反馈调整稳定性控制算法

当飞机在大回环飞行中,由于受到空气动力学的扰动较大,需要进行飞行姿态稳定性控制,传统方法采用分段线性化控制方法,在大扰动条件下,飞行过程中各段的控制误差不断方法,导致飞行稳定性不好。提出一种基于自适应反步跟踪的飞行器反馈调整稳定性控制算法。构建大回环飞行中的飞行稳定性控制的参量模型系统,考虑外界干扰的情况下,进行飞行器反馈调整稳定性控制目标函数构建,采用自适应反步跟踪方法拟合控制过程的状态误差响应,实现控制器优化设计。仿真结果表明,采用该算法进行飞行器的稳定性控制,系统误差受到外界扰动的影响较小,控制器的自适应收敛性较高,展示了较好的应用性能。     

Recursive and Trellis-Based Feedback Reduction for MIMO-OFDM with Rate-Limited Feedback

We investigate an adaptive MIMO-OFDM system with a feedback link that can only convey a finite number of bits. We consider three different transmitter configurations: i) beamforming applied per OFDM subcarrier, ii) precoded spatial multiplexing applied per subcarrier, and iii) precoded orthogonal space time block coding applied per subcarrier. Depending on the channel realization, the receiver selects the optimal beamforming vector or precoding matrix from a finite-size codebook on each subcarrier, and informs the transmitter through finite-rate feedback. Exploiting the fact that the channel responses across OFDM subcarriers are correlated, we propose two methods to reduce the amount of feedback. One is recursive feedback encoding that selects the optimal beamforming/precoding choices sequentially across the subcarriers, and adopts a smaller-size time-varying codebook per subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal decisions for all subcarriers at once along a trellis structure via the Viterbi algorithm. Our methods are applicable to different transmitter configurations in a unified fashion. Simulation results demonstrate that the trellis-based approach outperforms the recursive method as well as an existing interpolation-based alternative at high signal-to-noise-ratio, as the latter suffers from "diversity loss"     

Feedback control methods for task regulation by electricalstimulation of muscles

Three feedback control algorithms of varying complexity were compared for controlling three different tasks during electrical stimulation of muscles. Two controllers use stimulus pulse width (or recruitment) modulation to grade muscle force (the fixed parameter, first-order PW controller and the adaptive controller). The third controller varies both stimulus pulse width and period simultaneously for muscle force modulation (the PW/SP controller described in the comparison paper). The three tasks tested were isometric torque control, unloaded position tracking, and control of transitions between isometric and unloaded conditions. The first task involved the muscle recruitment nonlinearity. The second task added the effects of muscle length-tension and force-velocity nonlinearities. The third task included a sudden changes in external loading conditions. The comparative evaluation was carried out in an intact cat ankle joint with stimulation of tibialis anterior and medial gastrocnemius muscles. The simplest PW controller demonstrated robust control for all tasks. The PW/SP controller improved the performance of the PW controller significantly for control of isometric torque and load transition, but only slightly for control of unloaded joint position. However, the adaptive controller did not consistently achieve a significant improvement in performance compared with the PW controller for any task. Results suggest that muscle length-tension and force-velocity nonlinearities affect the performance of these controllers similarly within the tested ranges of movement amplitudes and speeds. Abrupt changes in the system, such as those due to recruitment nonlinearity and external loading transitions, tend to limit the performance of the adaptive controller. The study provides guidelines for choosing control algorithms for neural prostheses.     

Feedback control of the nuclear magnetization state: experimental results

In a previous paper (Proc. Soc. Magn. Reson. Med., San Francisco, CA, USA, 1991), the authors investigated feedback control of the nuclear magnetization state. This strategy facilitates the optimization of the pulse parameters during the imaging sequence. In this work, results from a series of experiments used to test the theoretical predictions are presented. Two groups of experiments were performed using a commercial imager and a small sample of distilled water. In the first group of experiments the control objective is to regulate the magnetization orientation to a constant reference angle. The results show that a closed-loop system produces the desired orientation. In contrast, an open-loop input results in an appreciable error between desired and measured orientation. A second group of experiments shows that a closed-loop system can force the magnetization orientation to track a desired trajectory. In both groups, the closed-loop experimental and simulation results are in excellent agreement. The application of feedback control to MRI and spectroscopy is discussed.     

激光焊接金刚石锯片的特征声信号反馈控制

激光焊接金刚石锯片过程中形成的光致等离子体伴随着具有明显特征的声响,这种特征声信号可看成是由频率为16kHz左右的等离子体声信号被一周期信号所调制,周期信号的频率约为300Hz。介绍了特征声信号的提取方法及其用于激光焊接金刚石锯片的反馈控制系统构成和基本原理。试验结果表明,采用特征声信号反馈控制的激光焊接金刚石锯片在焊接缺陷方面优于无反馈控制激光焊接方法。     

Multiuser Diversity with Binary Feedback

In this paper, we propose a scheduling algorithm that reduces the feedback load with no penalty loss in the spectral efficiency when compared to the optimal selective diversity scheme (Harthi et al. in IEEE Trans Wirel Commun 6(1), 2007). In order to reduce the feedback rate, a two stage probing technique is introduced. In the first stage, the scheduler estimates the threshold level in which the best user is likely to be found. In the second stage, the scheduler permits two users to contend for a mini-slot using only one bit of feedback information per user. After deriving closed-form expressions for the feedback load, we compare the performance of our algorithm with the discrete rate switch-based multiuser diversity (DSMUDiv) scheme (Harthi et al. in IEEE Trans Wirel Commun 6(1), 2007) and the optimal selective diversity scheme. Numerical results show that our scheme further reduces the feedback load, rate and guard time when compared to both the DSMUDiv and the optimal selective diversity schemes under slow Rayleigh fading assumption.     

Opportunistic Beamforming with Limited Feedback

This work investigates the following question: subject to strictly limited (finite-rate) feedback in a multi-user multi-antenna system, what channel state information (CSI) should we send back to the transmitter, and how should it be used? Considering the class of single-beam systems, we suggest a combination of beamforming (array gain) and multi-user diversity. It has been shown that in single antenna systems, one bit of feedback per user can capture almost all gains available due to multi-user diversity, therefore we propose and analyze a compound strategy that uses one bit for multi-user diversity and any further feedback bits for beamforming. We obtain the scaling laws of this compound strategy, showing that it scales as well as any single-beam system with full transmit-CSI.     

MU-MISO Transmission with Limited Feedback

Downlink multi-user transmission techniques that allow several users to be served simultaneously in frequency and time have been recognized as a promising means to increase system capacity. However they require accurate channel state information (CSI) at the base station (BS) such that appropriate signal processing can be performed to separate multiple users in the space domain. In practice however, CSI cannot be perfectly known to the BS due to the capacity-limited feedback channel in FDD systems for instance. In this letter we investigate multiuser multiple-input single-output (MU-MISO) transmission with limited feedback. In particular we identify the useful information that the BS needs to deal with inter-user interference and a codebook design is derived accordingly. In addition, an adaptive threshold-based feedback approach is proposed, where only users with good feedback quality are allowed to do feedback. It is shown that the adaptive scheme can effectively improve the system performance given a fixed number of feedback bits.     

Feedback control of limit cycles: a switching control strategy based on nonsmooth bifurcation theory

In this paper, we present a method to control limit cycles in smooth planar systems making use of the theory of nonsmooth bifurcations. By designing an appropriate switching controller, the occurrence of a corner-collision bifurcation is induced on the system and the amplitude and stability properties of the target limit cycle are controlled. The technique is illustrated through a representative example.     

Feedback control applied to survivability: a host-based autonomic defense system

We address the problem of information system survivability, or dynamically preserving intended functionality & computational performance, in the face of malicious intrusive activity. A feedback control approach is proposed which enables tradeoffs between the failure cost of a compromised information system and the maintenance cost of ongoing defensive countermeasures. Online implementation features an inexpensive computation architecture consisting of a sensor-driven recursive estimator followed by an estimate-driven response selector. Offline design features a systematic empirical procedure utilizing a suite of mathematical modeling and numerical optimization tools. The engineering challenge is to generate domain models and decision strategies offline via tractable methods, while achieving online effectiveness. We illustrate the approach with experimentation results for a prototype autonomic defense system which protects its host, a Linux-based web-server, against an automated Internet worm attack. The overall approach applies to other types of computer attacks, network-level security and other domains which could benefit from automatic decision-making based on a sequence of sensor measurements.     

基于电流反馈信号的智能扬声器系统

提出了一种面向小型扬声器的智能扬声器系统。该系统能够依据扬声器电流反馈信号在线跟踪辨识扬声器的线性参数,并利用辨识得到的参数对扬声器进行自适应的低频均衡。推导得出了扬声器自适应均衡目标函数截止频率与其线性参数的关系。仿真实验结果表明,该均衡算法能在约束扬声器振膜振幅的同时,有效扩展和提升扬声器的低频响应。     

Orthogonal Space-Time Block Codes with Feedback

In this paper we consider how Orthogonal Space-Time Block Codes (OSTBC) can be used in the presence of feedback from the receiver to the transmitter. First, we survey how some of the feedback techniques for AWGN channels with fading can be applied to OSTBC. Then we consider a simple scheme with diagonal weighting. The optimal diagonal weighting matrix, which minimizes the probability of error, is derived. The optimal weights depend on the channel and, hence, a feedback becomes necessary. However, the required feedback can be accomplished using log₂ (n _t) bits, where n _t is the number of transmit antennas. Simulations show that relatively significant gains can be achieved with the diagonal weighting scheme. In a practical system it is quite possible that the bits that are fed back to the transmitter are in error. In that case we show that there will be a loss of diversity. To overcome this loss, we develop weighting schemes that are error tolerant and always perform better than the unweighted OSTBC (even in the presence of feedback errors).     

MIMO Broadcast Scheduling with Limited Feedback

We consider multiuser scheduling with limited feedback of partial channel state information in MIMO broadcast channels. By using spatial multiplexing at the base station (BS) and antenna selection for each user, we propose a multiuser scheduling method that allocates independent information streams from all M transmit antennas to the M most favorable users with the highest signal-to-interference-plus-noise ratio (SINR). A close approximation of the achievable sum-rate throughput for the proposed method is obtained and shown to match the simulation results very well. Moreover, two reduced feedback scheduling approaches are proposed. In the first approach, which we shall refer to as selected feedback scheduling, the users are selected based on their SINR compared to a predesigned threshold. Only those selected users are allowed to feed back limited information to the BS. The resultant feedback load and achievable throughput are derived. It will then be demonstrated that with a proper choice of the threshold, the feedback load can be greatly reduced with a negligible performance loss. The second reduced feedback scheduling approach employs quantization for each user, in which only few bits of quantized SINR are fed back to the BS. Performance analysis will show that even with only 1-bit quantization, the proposed quantized feedback scheduling approach can exploit the multiuser diversity at the expense of slight decrease of throughput.