Hedi Khammari

Resource Allocation for Transmit Hybrid Beamforming in Decoupled Millimeter Wave Multiuser-MIMO Downlink

This paper presents a study on joint radio resource allocation and hybrid precoding in multi-carrier massive multiple-input multiple-output communications for 5G cellular networks. In this paper, we present the resource allocation algorithm to maximize the proportional fairness (PF) spectral efficiency under the per subchannel power and the beamforming rank constraints. Two heuristic algorithms are designed. The proportional fairness hybrid beamforming algorithm provides the transmit precoder with a proportional fair spectral efficiency among users for the desired number of radio-frequency (RF) chains. Then, we transform the number of RF chains or rank constrained optimization problem into convex semidefinite programming (SDP) problem, which can be solved by standard techniques. Inspired by the formulated convex SDP problem, a low-complexity, two-step, PF-relaxed optimization algorithm has been provided for the formulated convex optimization problem. Simulation results show that the proposed suboptimal solution to the relaxed optimization problem is near-optimal for the signal-to-noise ratio

A qualitative characterization of the PMSM dynamics

SNR\leq 10

On some parametric and phase space singularities in PMSM submitted to FOC drive

dB and has a performance gap not greater than 2.33 b/s/Hz within the SNR range 0–25 dB. It also outperforms the maximum throughput and PF-based hybrid beamforming schemes for sum spectral efficiency, individual spectral efficiency, and fairness index.

Phase space singularities in speed field oriented control of PMSM

A qualitative characterization of the PMSM behavior, based on certain characteristic bifurcation structures is discussed. The equilibrium points of the PMSM were derived from the mathematical model and the stability of the origin equilibrium stability conditions were given. Foliation of the parametric plane and its role to understand the bifurcation mechanisms was illustrated. A particular structure including bifurcations of codimension one and two was identified.

Bifurcation and chaos phenomena appearing in induction motor under variation of PI controller parameters

This paper describes the occurrence of certain dynamic responses of the permanent magnet synchronous motor submitted to a FOC control under a parameter variation. In addition to the transition between limit cycles and equilibrium points due to the Hopf bifurcation, the multistability property is put into evidence by the identification of several attractors for the same motor and control parameter sets and for different sets of initial conditions. An illustration of the domains or basins of attractions of different attractors is given in a three dimensional phase space. Analytical expressions of equilibrium point coordinates are determined from the differential system equations; their stability can be known from the characteristic polynomial solutions.

Bifurcation scenario and chaos detection under variation of PI controller and induction motor parameters

The existence and the stability of phase space singularities namely equilibrium points and limit cycles are discussed. The coexistence of many stable behaviors for a given set of system parameters and for different initial conditions is presented putting evidence into the most exciting phenomena in nonlinear dynamics, referred to as multistability. A classical method of speed control of synchronous motor is applied in order to obtain numerical coordinates of equilibrium points. Their stability is analyzed by mean of Eigenvalues derived from Jacobian matrix of the system. The sets of initial conditions leading to such or such equilibrium point known as attraction basins are traced for different sets of system parameters whether that was close or far from critical points or bifurcation.