Search

In recent years, time-triggered communication protocols have been developed to support time-critical applications for in-vehicle communication. In this respect, the FlexRay protocol is likely to become the de facto standard. In this paper, we investigate the scheduling problem of periodic signals in the static segment of FlexRay. We identify and solve two subproblems and introduce associated performance metrics: 1) The signals have to be packed into equal-size messages to obey the restrictions of the FlexRay protocol, while using as little bandwidth as possible. To this end, we formulate a nonlinear integer programming (NIP) problem to maximize bandwidth utilization. Furthermore, we employ the restrictions of the FlexRay protocol to decompose the NIP and compute the optimal message set efficiently. 2) A message schedule has to be determined such that the periodic messages are transmitted with minimum jitter. For this purpose, we propose an appropriate software architecture and derive an integer linear programming (ILP) problem that both minimizes the jitter and the bandwidth allocation. A case study based on a benchmark signal set illustrates our results. Index Terms--FlexRay, integer programming, real time, scheduling, vehicular communication networks.

The FlexRay communication protocol is expected to be the de facto standard for high-speed, in-vehicle communication. In this paper, we formally investigate the scheduling problem for the dynamic segment (DS) of FlexRay. We take the bounds on the generation times and the timing requirements of the signals into consideration to propose a reservation-based scheduling approach that preserves the flexible medium access of the DS. To obtain efficient schedules, we formulate a nonlinear integer programming problem (NIP) that minimizes the required duration of the DS. This NIP is then decomposed into two linear binary integer programming problems to facilitate the computation of feasible message schedules. An experimental study illustrates our message scheduling approach for the DS of FlexRay. Index Terms--FlexRay, integer programming, real time, scheduling, vehicular communication networks.

Lane departure warning systems (LDWS) are an important element in improving driving safety. In this paper, we propose an embedded Advanced RISC Machines (ARM)-based real-time LDWS. As for software development, an improved lane detection algorithm based on peak finding for feature extraction is used to successfully detect lane boundaries. Then, a spatiotemporal mechanism using the detected lane boundaries is designed to generate appropriate warning signals. As for hardware implementation, a 1-D Gaussian smoother and a global edge detector are adopted to reduce noise effects in the images. By using the developed data transfer channel (DTC) in the reconfigurable field-programmable gate array (FPGA) module, the data transfer rate among the complementary metal-oxide-semiconductor (CMOS) imager module, liquid-crystal display (LCD) display module, and central processing unit (CPU) bus is about 25 frame/s for an image size of 256 x 256. In addition, the proposed departure warning algorithm based on spatial and temporal mechanisms is successfully executed on the presented ARM-based platform. The effectiveness of our system concludes that the lane detection rate is 99.57% during the day and 98.88% at night in a highway environment. The proposed departure mechanisms effectively generate effective warning signals and avoid most false warnings. Index Terms--Computer vision, embedded real-time system, lane departure warning system (LDWS), lane detection, smart vehicle, vanishing point.

Ultrawideband (UWB) is an emerging technology that is expected to achieve high data rate with low-power transmission and to enable quality-of-service (QoS)-based multimedia services over wireless personal area networks (WPANs). Currently, WiMedia alliance proposes the physical layer and medium access control (MAC) layer standards for WPANs. Although WiMedia MAC defines the QoS signaling mechanism, it does not specify the resource-allocation algorithm that will eventually provide the QoS guarantee. To address this issue, we first propose a novel traffic predictor for real-time variable bit rate (VBR) videos. Based on the proposed predictor, we then present a dynamic resource-allocation (DRA) algorithm to support real-time VBR video transmission over WiMedia-based WPANs. Simulation results indicate that the proposed traffic predictor and DRA algorithm significantly outperform other existing schemes. Index Terms--Medium access control (MAC), quality of service (QoS), ultrawideband (UWB), variable bit rate (VBR) video.

Unsymmetrical loading on a car like [mu]-split braking, side wind forces, or unilateral loss of fire pressure results in unexpected yaw disturbances that require yaw stabilization either by the driver or by an automatic driver-assist system. The use of two-degrees-of-freedom control architecture known as the model regulator is investigated here as a robust steering controller for such yaw stabilization tasks in a driver-assist system. The yaw stability-enhancing steering controller is designed in the parameter space to satisfy a frequency-domain mixed sensitivity constraint. To evaluate the resulting controller design, a real-time hardware-in-the-loop simulator is developed. Steering tests with and without the controller in this hardware-in-the-loop setup allow the driver to see the effect of the proposed controller to improve vehicle-handling quality. The hardware-in-the-loop simulation setup can also be used for real-time driver-in-the-loop simulation of other vehicle control systems. Index Terms--Hardware-in-the-loop simulation, model regulator, robust control, yaw stability control.

Recent trends in the telecommunication industry have been moving toward the development of ubiquitous information systems, where the provision of a plethora of advanced multimedia services should be possible, regardless of time and space limitations. An efficient and seamless delivery of multimedia services over various types of wireless networks is still a challenging task. The underlying difficulty consists of the disparity in the bandwidth availability over each network type. Indeed, the fundamental chailenge upon a handoff phenomenon in a heterogeneous wireless network consists of an efficient probing of the bandwidth availability of the new network, followed by a prompt adjustment of the data delivery rate. This paper presents a cross-layer approach that involves five layers, namely, physical, data link, application, network, and transport layers. The three former layers are used to anticipate the handoff occurrence and to locate the new point of attachment to the network. Based on their feedback, the transport layer is used then to probe the resources of the new network using low-priority dummy packets. Being the most widely used protocol for multimedia delivery, this paper addresses multimedia applications based on the Transmission Control Protocol (TCP) and the Real-time Transport Protocol (RTP). The design of the whole cross-layer architecture is discussed, and enhancements to the two protocols are proposed. The performance of the enhanced TCP and the RTP are evaluated and compared against existing schemes through extensive simulations. The obtained results are encouraging and promising for the delivery of multimedia services in heterogeneous wireless networks. Index Terms--Cross layer, heterogeneous wireless networks, next-generation wireless Internet, Real-time Transport Protocol (RTP), Transmission Control Protocol (TCP).

In this paper, we propose a real-time subcarrier, bit, and power allocation algorithm for orthogonal frequency-division multiplexing-based muitiuser communication systems in downlink transmission. Assuming that base stations know the channel gains of all subcarriers of all users, the proposed loading algorithm tries to minimize the required transmit power while satisfying the rate requirement and data error rate constraint of each user. The novel algorithm simultaneously determines subcarrier, bit, and power allocation by enhancing the suboptimal algorithm by Wong et al. while having the same computational complexity. The proposed scheme offers better performance in terms of transmit power than that of Wong et al., as demonstrated in the simulation results, whereas the performance of the scheme in Wong et al. was close to that of the optimal solution. Index Terms--Bit loading, multiuser orthogonal frequencydivision multiplexing (OFDM), subcarrier allocation.

In brake-by-wire systems, central controllers require accurate information about the clamp force between the brake pad and the disc as a function of pad displacement, which is usually denoted as the characteristic curve of the caliper. Due to aging, temperature, and other environmental variations, caliper characteristic curves vary with time. Therefore, automatic caliper calibration in real-time is vital for high-performance braking action and vehicle safety. Due to memory and processing-power limitations, the calibration technique should be memory efficient and of low computational complexity. In a typical electromechanicalbraking-system design, clamp force measurement variations with actuator displacement is hysteretic. This paper introduces a simple and memory-efficient real-time calibration technique in which a clamp-force model is fitted to the data samples around each hysteresis cycle. The model includes a Maxwell-slip model for the hysteresis caused by friction. Experimental results from the data recorded in various temperatures show that the proposed technique results in clamp force measurements with less than 0.7% error over the range of clamp-force variations. It is also shown that, by using these measurements, the characteristic curve can be accurately calibrated in real-time. Index Terms--Brake-by-wire (BBW), braking, calibration, force sensing, hysteresis.