Frame synchronization performance and analysis

The analysis used to generate the theoretical models showing the performance of the frame synchronizer is described for various frame lengths and marker lengths at various signal to noise ratios and bit error tolerances

Broadcast Coded Slotted ALOHA: A Finite Frame Length Analysis

We propose an uncoordinated medium access control (MAC) protocol, called all-to-all broadcast coded slotted ALOHA (B-CSA) for reliable all-to-all broadcast with strict latency constraints. In B-CSA, each user acts as both transmitter and receiver in a half-duplex mode. The half-duplex mode gives rise to a double unequal error protection (DUEP) phenomenon: the more a user repeats its packet, the higher the probability that this packet is decoded by other users, but the lower the probability for this user to decode packets from others. We analyze the performance of B-CSA over the packet erasure channel for a finite frame length. In particular, we provide a general analysis of stopping sets for B-CSA and derive an analytical approximation of the performance in the error floor (EF) region, which captures the DUEP feature of B-CSA. Simulation results reveal that the proposed approximation predicts very well the performance of B-CSA in the EF region. Finally, we consider the application of B-CSA to vehicular communications and compare its performance with that of carrier sense multiple access (CSMA), the current MAC protocol in vehicular networks. The results show that B-CSA is able to support a much larger number of users than CSMA with the same reliability.Comment: arXiv admin note: text overlap with arXiv:1501.0338

Distributed Plasticity Analysis of Frame Structures in Rate Form

Distributed plasticity beam column elements are able to efficiently track hysteretic nonlinear behavior of structures under static or dynamic loading. This is accomplished by a refined discretization of the element in control sections along its length, each one being represented by a set of longitudinal fibers. The global response of the element results from a two level integration. In the first the non-linear stress of every fiber is integrated across the cross-sectional area to derive the constitutive relation of the control section and then integration along the element’s length is proved sufficient to yield the current state of the element. This work focuses on the formulation of both displacement and force based beam-column elements where the internal variables that describe the element’s state, namely fiber stresses or strains are expressed in rate form, herein using Bouc-Wen hysteretic models. Both formulations are derived from a unified approach based on the two field Hellinger-Reissner potential which highlights their differences. For simplicity reasons the methodology is applied on plane frame elements based on Euler–Bernoulli kinematics. The main advantage of expressing the evolution of each internal variable through a differential equation offers the ability to solve the entire set simultaneously with the global structure’s equations of motion in state space form. Accurate solutions are derived from proper implementation of an efficient numerical ODE solver

NASTRAN nonlinear vibration analysis of beam and frame structures

A capability for the nonlinear vibration analysis of beam and frame structures suitable for use with NASTRAN level 15.5 is described. The nonlinearity considered is due to the presence of axial loads induced by longitudinal end restraints and lateral displacements that are large compared to the beam height. A brief discussion is included of the mathematical analysis and the geometrical stiffness matrix for a prismatic beam (BAR) element. Also included are a brief discussion of the equivalent linearization iterative process used to determine the nonlinear frequency, the required modifications to subroutines DBAR and XMPLBD of the NASTRAN code, and the appropriate vibration capability, four example problems are presented. Comparisons with existing experimental and analytical results show that excellent accuracy is achieved with NASTRAN in all cases

The metaphysics of Machian frame-dragging

The paper investigates the kind of dependence relation that best portrays Machian frame-dragging in general relativity. The question is tricky because frame-dragging relates local inertial frames to distant distributions of matter in a time-independent way, thus establishing some sort of non-local link between the two. For this reason, a plain causal interpretation of frame-dragging faces huge challenges. The paper will shed light on the issue by using a generalized structural equation model analysis in terms of manipulationist counterfactuals recently applied in the context of metaphysical enquiry by Schaffer (2016) and Wilson (2017). The verdict of the analysis will be that frame-dragging is best understood in terms of a novel type of dependence relation that is half-way between causation and grounding