We focus on a particular form of network coding, reverse carpooling, in a wireless network where the potentially coded transmitted messages are to be decoded immediately upon reception. The network is fixed and known,...
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We focus on a particular form of network coding, reverse carpooling, in a wireless network where the potentially coded transmitted messages are to be decoded immediately upon reception. The network is fixed and known, and the system performance is measured in terms of the number of wireless broadcasts required to meet multiple unicast demands. Motivated by the structure of the coding scheme, we formulate the problem as a linear program by introducing a flow variable for each triple of connected nodes. This allows us to have a formulation polynomial in the number of nodes. Using dual decomposition and projected subgradient method, we present a decentralized algorithm to obtain optimal routing schemes in presence of coding opportunities. We show that the primal sub-problem can be expressed as a shortest path problem on an edge-graph, and the proposed algorithm requires each node to exchange information only with its neighbors.
The density blobs present in the plasma edge in magnetic fusion devices can scatter radio frequency (RF) waves through refraction. Using the geometric optics approximation for the waves, a Fokker-Planck equation for t...
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ISBN:
(纸本)9781622763313
The density blobs present in the plasma edge in magnetic fusion devices can scatter radio frequency (RF) waves through refraction. Using the geometric optics approximation for the waves, a Fokker-Planck equation for the scattering of rays by a random distribution of blobs is derived. It is found that the scattering can diffuse the rays in space and in wave-vector space. The diffusion in space can make the rays miss their intended target region, and the diffusion in wave-vector space can broaden the wave spectrum and modify the wave damping profile. For ITER-type plasmas the wave scattering can lead to the electron cyclotron beams missing their intended target region of growing neoclassical tearing modes.
Kinodynamic planning algorithms like Rapidly-Exploring Randomized Trees (RRTs) hold the promise of finding feasible trajectories for rich dynamical systems with complex, nonconvex constraints. In practice, these algor...
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Kinodynamic planning algorithms like Rapidly-Exploring Randomized Trees (RRTs) hold the promise of finding feasible trajectories for rich dynamical systems with complex, nonconvex constraints. In practice, these algorithms perform very well on configuration space planning, but struggle to grow efficiently in systems with dynamics or differential constraints. This is due in part to the fact that the conventional distance metric, Euclidean distance, does not take into account system dynamics and constraints when identifying which node in the existing tree is capable of producing children closest to a given point in state space. We show that an affine quadratic regulator (AQR) design can be used to approximate the exact minimum-time distance pseudometric at a reasonable computational cost. We demonstrate improved exploration of the state spaces of the double integrator and simple pendulum when using this pseudometric within the RRT framework, but this improvement drops off as systems' nonlinearity and complexity increase. Future work includes exploring methods for approximating the exact minimum-time distance pseudometric that can reason about dynamics with higher-order terms.
We investigate a fast pedestrian localization framework that integrates the cascade-of-rejectors approach with the Histograms of Oriented Gradients (HoG) features on a data parallel architecture. The salient features ...
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We investigate a fast pedestrian localization framework that integrates the cascade-of-rejectors approach with the Histograms of Oriented Gradients (HoG) features on a data parallel architecture. The salient features of humans are captured by HoG blocks of variable sizes and locations which are chosen by the AdaBoost algorithm from a large set of possible blocks. We use the integral image representation for histogram computation and a rejection cascade in a sliding-windows manner, both of which can be implemented in a data parallel fashion. Utilizing the NVIDIA CUDA framework to realize this method on a Graphics Processing Unit (GPU), we report a speed up by a factor of 13 over our CPU implementation. For a 1280×960 image our parallel technique attains a processing speed of 2.5 to 8 frames per second depending on the image scanning density, which is similar to the recent GPU implementation of the original HoG algorithm in.
In this paper, we introduce a teaching module used in an oral communications course at mit to teach students how to (I) present technical material to a non-technical audience and (2) recover from things that may go wr...
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In this paper, we introduce a teaching module used in an oral communications course at mit to teach students how to (I) present technical material to a non-technical audience and (2) recover from things that may go wrong during a presentation. This module consists of various classroom activities that are all centered around an assignment in which students prepare a talk in order to explain a technical topic of their choosing to a non-technical audience. The entire experience culminates in a one-day conference attended by local high school students who serve as a live non-technical target audience for these talks. Here, we describe and discuss the various components of the module, with the hope that fellow practitioners will adopt and adapt the module for use in their home institution, and suggest modifications and improvements.
Medium-voltage DC electrical distribution is envisioned as a possible system for the warship of the future, bringing numerous advantages including a very power-dense architecture. This system takes the AC power produc...
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ISBN:
(纸本)9781617387043
Medium-voltage DC electrical distribution is envisioned as a possible system for the warship of the future, bringing numerous advantages including a very power-dense architecture. This system takes the AC power produced by generators, immediately rectifies all power to DC and distributes it throughout the ship, requiring inversion back to AC for all AC loads. The question then arises whether it makes sense instead to route two parallel buses: an AC bus for all 60 Hz. AC loads and a DC bus to service all other loads. We model these two theoretical distribution systems in a notional destroyer using a preliminary design tool under development in our laboratory and find that the two-bus system is more efficient and lighter.
We present an integral image algorithm that can run in real-time on a Graphics Processing Unit (GPU). Our system exploits the parallelisms in computation via the NIVIDA CUDA programming model, which is a software plat...
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We present an integral image algorithm that can run in real-time on a Graphics Processing Unit (GPU). Our system exploits the parallelisms in computation via the NIVIDA CUDA programming model, which is a software platform for solving non-graphics problems in a massively parallel high-performance fashion. This implementation makes use of the work-efficient scan algorithm that is explicated in. Treating the rows and the columns of the target image as independent input arrays for the scan algorithm, our method manages to expose a second level of parallelism in the problem. We compare the performance of the parallel approach running on the GPU with the sequential CPU implementation across a range of image sizes and report a speed up by a factor of 8 for a 4 megapixel input. We further investigate the impact of using packed vector type data on the performance, as well as the effect of double precision arithmetic on the GPU.
This paper considers the real-time motion planning problem for autonomous systems subject to complex dynamics, constraints, and uncertainty. Rapidly-exploring random trees (RRT) can be used to efficiently construct tr...
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ISBN:
(纸本)9781424474264
This paper considers the real-time motion planning problem for autonomous systems subject to complex dynamics, constraints, and uncertainty. Rapidly-exploring random trees (RRT) can be used to efficiently construct trees of dynamically feasible trajectories;however, to ensure feasibility, it is critical that the system actually track its predicted trajectory. This paper shows that under certain assumptions, the recently proposed closed-loop RRT (CL-RRT) algorithm can be used to accurately track a trajectory with known error bounds and robust feasibility guarantees, without the need for replanning. Unlike open-loop approaches, bounds can be designed on the maximum prediction error for a known uncertainty distribution. Using the property that a stabilized linear system subject to bounded process noise has BIBO-stable error dynamics, this paper shows how to modify the problem constraints to ensure long-term feasibility under uncertainty. Simulation results are provided to demonstrate the effectiveness of the closed-loop RRT approach compared to open-loop alternatives.
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