Browsing by Author "Mirfakhraie, Tina"
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Item Optomal three-time slot distributed beamforming for two-way relaying(2010-08-01) Mirfakhraie, Tina; Shahbazpanahi, ShahramIn this study, we consider a relay network, with two transceivers and r relay nodes. We assume that each of relays and the two transceivers have a single antenna. For establishing the connection between these two transceivers, we propose a two-way relaying scheme which takes three phases (time slots) to accomplish the exchange of two information symbols between the two transceivers. In the first and second phases, the transceivers, transmit their signals, toward the relays, one after other. The signals that are received by relays are noisy versions of the original signals. Each relay, multiplies its received signal by a complex beamforming coefficient to adjust the phase and amplitude of the signal. Then in the third phase, each relay transmits the summation of so-obtained signals to both transceivers. Our goal is to find the optimal values of transceivers’ transmit powers and the optimal values of the beamforming coefficients by minimizing the total transmit power subject to quality of service constraints. In our approach, we minimize the total transmit power under two constraints. These two constraints are used to guarantee that the transceivers’ receive Signal-to-Noise Ratios (SNRs) are above given thresholds. To solve the underlying optimization problem, we develop two techniques. The first technique is a combination of a two-dimensional search and Second-Order Convex Cone Programming (SOCP). More specifically, the set of feasible values of transceivers’ transmit powers is quantized into a sufficient fine grid. Then, at each vertice of this grid, an SOCP problem is solved to obtain the beamforming coefficients such that for the given pair of transceivers’ transmit powers, the total transmit power is minimized. The pair of the transceivers’ transmit powers, which result in the smallest possible value of the total transmit power, leads us to the solution of the problem. This approach requires a two-dimensional search and solving an SOCP problem at each point of the corresponding two-dimensional grid. Thus, it can be prohibitively expensive in terms of computational complexity. As a second method, we resort to a gradient based steepest descent technique. Our simulation results show that this second technique performs very close to the optimal two-dimensional search based algorithm. Finally we compare our technique with multi-relay distributed beamforming schemes, previously developed in literature and show that our three-phase two-way relaying scheme requires less total power as compared to the two-phase two-way relaying method. On the other hand, the two-phase two-way relaying achieves higher data rates when compared with three-phase two-way relaying for the same total transmit power. Also, we observe that the three-phase scheme has more degrees of freedom while multi-relay distributed beamforming schemes, previously developed in literature appears to be more bandwidth efficient.Item A wireless communication based active safety system for articulated heavy vehicles(2020-04-01) Mirfakhraie, Tina; Liscano, Ramiro; He, YupingTo date, various active safety systems, have been developed to improve the safety of road vehicles. This dissertation presents a novel active trailer steering (ATS) system using wireless communication to exchange data among controllers and sensors allocated on the leading and trailing units of an articulated heavy vehicle (AHV). Conventionally, integrating the sensors, actuators, and controllers located on the leading and trailing units of the vehicle needs wired connections. The physical connection at the articulation joint increases the risk of disconnections and damages. Adopting a wireless communication system displays pronounced advantages, including flexibility, cost-effectiveness and ease of maintenance. For AHV's lateral stability control using wireless communication based ATS, addressing the problem of data delay and loss is the main challenge of this study. Innovative solutions have been proposed to tackle the challenges and numerical simulations have been conducted to evaluate the applicability and effectiveness of the proposed techniques for wireless communication based ATS. To this end, a realistic co-simulation platform is designed: the wireless communication based ATS system is constructed in MATLAB/Simulink; the virtual AHV is built in TruckSim; by means of integrating the ATS system and the virtual AHV, the co-simulation can be performed. As a preliminary design, a gain scheduler is introduced to compensate for the effect of data delay and stabilize the AHV. Later, in order to ensure the performance of the ATS control, a Kalman filter-based estimator is introduced. The estimator uses the available dynamic data to estimate the current states of the AHV in case some sensor data is not available. Several design parameters of the communication system based on dedicated short range communication (DSRC) standard such as modulation, quantization, channel estimation algorithm and transmit diversity have been studied. The effect of each parameter on AHV lateral stability is reviewed to propose proper configuration of the DSRC standard. Finally, an adaptive extended Kalman filter is introduced to mitigate the effects of asynchronous time delay on the AHV lateral stability. This thesis initiates the concept of wireless communication based ATS systems for AHVs and provides valuable guidance for such design and development.