In this contribution, we suggest two proposals to achieve fast, real-time lane-keeping control for Autonomous Ground Vehicles (AGVs). The goal of lane-keeping is to orient and keep the vehicle within ...a given reference path using the front wheel steering angle as the control action for a specific longitudinal velocity. While nonlinear models can describe the lateral dynamics of the vehicle in an accurate manner, they might lead to difficulties when computing some control laws such as Model Predictive Control (MPC) in real time. Therefore, our first proposal is to use a Linear Parameter Varying (LPV) model to describe the AGV's lateral dynamics, as a trade-off between computational complexity and model accuracy. Additionally, AGV sensors typically work at different measurement acquisition frequencies so that Kalman Filters (KFs) are usually needed for sensor fusion. Our second proposal is to use a Dual-Rate Extended Kalman Filter (DREFKF) to alleviate the cost of updating the internal state of the filter. To check the validity of our proposals, an LPV model-based control strategy is compared in simulations over a circuit path to another reduced computational complexity control strategy, the Inverse Kinematic Bicycle model (IKIBI), in the presence of process and measurement Gaussian noise. The LPV-MPC controller is shown to provide a more accurate lane-keeping behavior than an IKIBI control strategy. Finally, it is seen that Dual-Rate Extended Kalman Filters (DREKFs) constitute an interesting tool for providing fast vehicle state estimation in an AGV lane-keeping application.
In this paper, a two-wheel drive unmanned ground vehicle (UGV) path-following motion control is proposed. The UGV is equipped with encoders to sense angular velocities and a beacon system which ...provides position and orientation data. Whereas velocities can be sampled at a fast rate, position and orientation can only be sensed at a slower rate. Designing a dynamic controller at this slower rate implies not reaching the desired control requirements, and hence, the UGV is not able to follow the predefined path. The use of dual-rate extended Kalman filtering techniques enables the estimation of the fast-rate non-available position and orientation measurements. As a result, a fast-rate dynamic controller can be designed, which is provided with the fast-rate estimates to generate the control signal. The fast-rate controller is able to achieve a satisfactory path following, outperforming the slow-rate counterpart. Additionally, the dual-rate extended Kalman filter (DREKF) is fit for dealing with non-linear dynamics of the vehicle and possible Gaussian-like modeling and measurement uncertainties. A Simscape Multibody™ (Matlab®/Simulink) model has been developed for a realistic simulation, considering the contact forces between the wheels and the ground, not included in the kinematic and dynamic UGV representation. Non-linear behavior of the motors and limited resolution of the encoders have also been included in the model for a more accurate simulation of the real vehicle. The simulation model has been experimentally validated from the real process. Simulation results reveal the benefits of the control solution.
This paper develops a novel optimization of partial transmit sequences (PTS) with phase quantization to reduce the peak-to-average-power ratio (PAPR) of orthogonal frequency-division multiplexing ...(OFDM) signals and enable data detection without side information. Since the formulated optimization problem is non-convex and has exponential time complexity, we employ a convex relaxation method to convert the original optimization problem into a series of convex programming whose solutions converge to a sub-optimal point satisfying the Karush-Kuhn-Tucker (KKT) conditions in polynomial time. Moreover, the obtained phase factors are quantized to enable the maximum likelihood (ML) phase estimation at the receiver, hence removing the need of sending side information. Analytical and numerical results are provided to show that our proposed PTS design achieves better PAPR reduction over existing PTS methods, while no performance degradation is incurred in data detection when the number of phase factors is properly chosen.
•A novel delay-independent control solution is presented for a networked control system.•The control structure integrates a packet-based control strategy with predictor-based and dual-rate control ...techniques.•Control system stability is ensured in terms of linear matrix inequalities (LMIs).•The effectiveness of the proposed method is illustrated via simulation and experimentally validated by means of a robotic platform.•The control solution is able to reach the nominal (no-dropout, no-delay) performance.
In this paper, a novel delay-independent control structure for a networked control system (NCS) is proposed, where packet-based control strategies with predictor-based and dual-rate control techniques are integrated. The control solution is able to cope with some networked communication problems such as time-varying delays, packet dropouts and packet disorder. In addition, the proposed approach enables to reduce network load, and usage of connected devices, while maintaining a satisfactory control performance. As a delay-independent control solution, no network-induced delay measurement is needed for controller implementation. In addition, the control scheme is applicable to open-loop unstable plants. Control system stability is ensured in terms of linear matrix inequalities (LMIs). Simulation results show the main benefits of the control approach, which are experimentally validated by means of a Cartesian-robot-based test-bed platform.
This paper presents an extended Kalman-filter-based sensor fusion approach, which enables path-following control of a holonomic mobile robot with four mecanum wheels. Output measurements of the ...mobile platform may be sensed at different rates: odometry and orientation data can be obtained at a fast rate, whereas position information may be generated at a slower rate. In addition, as a consequence of possible sensor failures or the use of lossy wireless sensor networks, the presence of the measurements may be nonuniform. These issues may degrade the path-following control performance. The consideration of a nonuniform dual-rate extended Kalman filter (NUDREKF) enables us to estimate fast-rate robot states from nonuniform, slow-rate measurements. Providing these estimations to the motion controller, a fast-rate control signal can be generated, reaching a satisfactory path-following behavior. The proposed NUDREKF is stated to represent any possible sampling pattern by means of a diagonal matrix, which is updated at a fast rate from the current, existing measurements. This fact results in a flexible formulation and a straightforward algorithmic implementation. A modified Pure Pursuit path-tracking algorithm is used, where the reference linear velocity is decomposed into Cartesian components, which are parameterized by a variable gain that depends on the distance to the target point. The proposed solution was evaluated using a realistic simulation model, developed with Simscape Multibody (Matlab/Simulink), of the four-mecanum-wheeled mobile platform. This model includes some of the nonlinearities present in a real vehicle, such as dead-zone, saturation, encoder resolution, and wheel sliding, and was validated by comparing real and simulated behavior. Comparison results reveal the superiority of the sensor fusion proposal under the presence of nonuniform, slow-rate measurements.
Background Precautionary labeling is used to warn consumers of the presence of unintended allergens, but the lack of agreed allergen thresholds can result in confusion and risk taking by patients ...with food allergy. The lack of data on threshold doses below which subjects are unlikely to react is preventing the development of evidence-based allergen management strategies that are understood by clinician and patient alike. Objective We sought to define threshold dose distributions for 5 major allergenic foods in the European population. Methods Patients with food allergy were drawn from the EuroPrevall birth cohort, community surveys, and outpatient clinic studies and invited to undergo a food challenge. Low-dose, double-blind, placebo-controlled food challenges were undertaken with commercially available food ingredients (peanut, hazelnut, celery, fish, and shrimp) blinded into common matrices. Dose distributions were modeled by using interval-censoring survival analysis with 3 parametric approaches. Results Of the 5 foods used for challenge, 4 produced similar dose distributions, with estimated doses eliciting reactions in 10% of the allergic population (ED10 ), ranging from 1.6 to 10.1 mg of protein for hazelnut, peanut, and celery with overlapping 95% CIs. ED10 values for fish were somewhat higher (27.3 mg of protein), although the CIs were wide and overlapping between fish and plant foods. Shrimp provided radically different dose distributions, with an ED10 value of 2.5 g of protein. Conclusion This evidence base will contribute to the development of reference doses and action levels for allergens in foods below which only the most sensitive subjects might react.
Zero-CP OFDM for DOCSIS-Based CATV Networks Nguyen, Tung T.; Nguyen, Ha H.; Eric Salt, J. ...
IEEE transactions on broadcasting,
2019-Dec., 2019-12-00, 20191201, Letnik:
65, Številka:
4
Journal Article
Recenzirano
The current version of the data over cable service interface specification (DOCSIS), which is DOCSIS 3.1, is markedly different from previous versions in that orthogonal frequency-division ...multiplexing (OFDM) is used together with high-density QAM constellations (up to 4096-QAM) in both the downstream and upstream directions to facilitate high data rates. This is in a sharp contrast with the single-carrier modulation techniques used in prior versions of DOCSIS. Despite many advantages, a drawback of OFDM is the insertion of a cyclic prefix (CP) at the beginning of each transmitted OFDM symbol to mitigate inter-symbol interference (ISI). The CP, which is configurable, but can be as large as 25% of the symbol time for DOCSIS 3.1 downstream transmission, does not carry useful data and therefore reduces the overall transmission throughput. In general, not only the channel but also the transceivers' digital filters determine the ISI and therefore the length of the CP. In this paper, the aspects that determine the CP length are thoroughly addressed. A novel technique to eliminate the CP is introduced and analyzed. It is demonstrated that the CP can be completely removed with a negligible effect on the transmission performance using this technique. Moreover, the proposed technique requires only a modest amount of hardware, making it a promising candidate to be included in the a future version of DOCSIS.
Tiered rates are an effective tool for conserving water in California, but they are subject to the courts' interpretation and consequent rulings; with guidance, water agencies can navigate this ...shifting legislative landscape as they assess and develop rate structures.
This paper presents an orthogonal frequency division multiple access (OFDMA) channel estimation technique that jointly considers the effects of coarse timing error and multipath propagation. Many ...conventional approaches only consider an optimistic scenario where timing synchronization is perfect and each of the channel delays is an integer number of system samples. In realistic scenarios timing offsets and echo delays are not integer multiples of the system's sampling period. This leads to poor estimation and consequently reduces the system's overall performance. This paper proposes a novel iterative channel estimation technique, which considers the practical scenario of fractional timing error and nonsample-spaced echo delays. The proposed method does not require channel state information (e.g., second-order statistics of the channel impulse responses or the noise power). Moreover, timing error can be conveniently obtained with the proposed technique. Simulation results show that, when comparing OFDMA channel estimation techniques under realistic data over cable service interface specification 3.1 channel conditions, the proposed algorithm significantly outperforms all conventional methods known to the authors.
This paper introduces a packet-based dual-rate control strategy to face time-varying network-induced delays, packet dropouts and packet disorder in a Networked Control System. Slow-rate sensing ...enables to achieve energy saving and to avoid packet disorder. Fast-rate actuation makes reaching the desired control performance possible. The dual-rate PID controller is split into two parts: a slow-rate PI controller located at the remote side (with no permanent communication to the plant) and a fast-rate PD controller located at the local side. The remote side also includes a prediction stage in order to generate the packet of future, estimated slow-rate control actions. These actions are sent to the local side and converted to fast-rate ones to be used when a packet does not arrive at this side due to the network-induced delay or due to occurring dropouts. The proposed control solution is able to approximately reach the nominal (no-delay, no-dropout) performance despite the existence of time-varying delays and packet dropouts. Control system stability is ensured in terms of probabilistic Linear Matrix Inequalities (LMIs). Via real-time control for a Cartesian robot, results clearly reveal the superiority of the control solution compared to a previous proposal by authors.
•Implementation of a packet-based dual-rate control strategy to face time-varying delays, and packet dropout and disorder in a NCS•Introduction of a prediction stage at the remote side, which contains a state resetting procedure, useful for unstable plants.•Communication between controller and plant through a real shared medium: UDP communication.•Facing time-varying delays and 30% of packet loses without significant degradation of the performance.•Control system stability is ensured in terms of probabilistic Linear Matrix Inequalities (LMIs).
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