| |  | Xu, L. | Robust Model-Based Fault Detection for a Roll Stability Control System read moreAbstract: Fault management is critical for a vehicle active safety system. Since a sensor fault may not always be detectable by a sensor self-test or an electronic monitoring system whose detection often relies on out-of-range signals, a redundancy check is warranted for the detection of an in-range signal fault. In this paper, an in-vehicle roll rate sensor failure detection scheme utilizing analytical redundancy is presented. The vehicle is assumed to be equipped with a steering wheel angle sensor, a yaw rate sensor, a lateral accelerometer, and wheel speed sensors in addition to the roll rate sensor. Due to the wide variation of vehicle dynamics under a vast operating range, such as various and dynamically changing road super-elevations and road grades, the detection of a roll rate signal fault using analytical redundancy is particularly challenging. These challenges, as well as the robustness and performance of the proposed scheme are discussed. The robust performance of the proposed scheme, over model uncertainties and road disturbances, is illustrated analytically and validated through experimental test data. The analytical illustrations include three elements: a robust estimation of the vehicle roll angle, a dynamic compensation of both electrical and kinematics-induced biases in the roll rate signal, and a directionally sensitive design of a robust observer which decouples the model uncertainties and disturbances from the fault. The experimental verifications of no false positive and/or no false negative were taken with a variety of maneuvers and road conditions on several vehicle test platforms  This article is not yet tagged | 2007 |
| | | Xu, L. | Iterative Generalized-Likelihood Ratio Test for MIMO Radar read moreAbstract: We consider a multiple-input multiple-output (MIMO) radar system where both the transmitter and receiver have multiple well-separated subarrays with each subarray containing closely spaced antennas. Because of this general antenna configuration, both the coherent processing gain and the spatial diversity gain can be simultaneously achieved. We compare several spatial spectral estimators, including Capon and APES, for target detection and parameter estimation. We introduce a generalized- likelihood ratio test (GLRT) and a conditional generalized- likelihood ratio test (cGLRT) for the general antenna configuration. Based on GLRT and cGLRT, we then propose an iterative GLRT (iGLRT) procedure for target detection and parameter estimation. Via several numerical examples, we show that iGLRT can provide excellent detection and estimation performance at a low computational cost. This article is not yet tagged | 2007 |
| | | Lau, A. P. | Performance of Receivers and Detection Algorithms for Modal Multiplexing in Multimode Fiber Systems read moreAbstract: We consider a multimode fiber system exploiting modal multiplexing using various direct-detection photoreceiver structures with zero-forcing detection algorithm. We show in theory how the squaring operation of the receivers and multimode excitations by a bit stream introduce bit detection errors even in the absence of noise. Numerical examples are provided to illustrate their impacts on system performance measured in terms of the bit-error ratio. This article is not yet tagged | 2007 |
| | | Rhee, I. | Limitations of Equation-Based Congestion Control read moreAbstract: We study limitations of an equation-based congestion control protocol, called TCP-Friendly Rate Control (TFRC). It examines how the three main factors that determine TFRC throughput, namely, the TCP-friendly equation, loss event rate estimation, and delay estimation, can influence the long-term throughput imbalance between TFRC and TCP. Especially, we show that different sending rates of competing flows cause these flows to experience different loss event rates. There are several fundamental reasons why TFRC and TCP flows have different average sending rates, from the first place. Earlier work shows that the convexity of the TCP-friendly equation used in TFRC causes the sending rate difference. We report two additional reasons in this paper: 1) the convexity of $1/x$ where $x$ is a loss event period and 2) different retransmission timeout period (RTO) estimations of TCP and TFRC. These factors can be the reasons for TCP and TFRC to experience initially different sending rates. But we find that the loss event rate difference due to the differing sending rates greatly amplifies the initial throughput difference; in some extreme cases, TFRC uses around 20 times more, or sometimes 10 times less, bandwidth than TCP. Despite these factors influencing the throughput difference, we also find that simple heuristics can greatly mitigate the problem. This article is not yet tagged | 2007 |
| | | Trizna, D. | Target Classification and Remote Sensing of Ocean Current Shear Using a Dual-Use Multifrequency HF Radar read moreAbstract: In this paper, we describe a high-frequency (HF) radar capable of multifrequency operation over the HF band for dual-use application to ship classification and mapping ocean current shear and vector winds. The radar is based on a digital transceiver peripheral component interconnect (PCI) card family that supports antenna arrays of four to 32 elements with a single computer, with larger arrays possible using multiple computers and receiver cards. The radar makes use of broadband loop antennas for receive elements, and a number of different possibilities for transmit antennas, depending on the operating bandwidth desired. An option exists in the choice of monostatic or multistatic operation, the latter providing the ability to use several transmit sites, with all radar echo signal reception and processing conducted at a single master receiver site. As applications for such a multifrequency radar capability, we show measurement and modeling examples of multiple frequency HF radar cross section (RCS) of ships as an approach to ship target classification. Results of using 32 radar frequencies to measure the fine structure in ocean current vertical shear are also shown, providing evidence of one edge of a 1-3-m deep uniform flow masked at the surface by wind-driven current shear in a different direction. Other applications of current-shear measurements, such as vector wind mapping and volumetric current estimation in coastal waters, are also discussed This article is not yet tagged | 2006 |
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