187,592 research outputs found
Adaptive Resource Management for Uncertain Execution Platforms
Embedded systems are becoming increasingly complex. At the same time, the components that make up the system grow more uncertain in their properties. For example, current developments in CPU design focuses on optimizing for average performance rather than better worst case performance. This, combined with presence of 3rd party software components with unknown properties, makes resource management using prior knowledge less and less feasible. This thesis presents results on how to model software components so that resource allocation decisions can be made on-line. Both the single and multiple resource case is considered as well as extending the models to include resource constraints based on hardware dynam- ics. Techniques for estimating component parameters on-line are presented. Also presented is an algorithm for computing an optimal allocation based on a set of convex utility functions. The algorithm is designed to be computationally efficient and to use simple mathematical expres- sions that are suitable for fixed point arithmetics. An implementation of the algorithm and results from experiments is presented, showing that an adaptive strategy using both estimation and optimization can outperform a static approach in cases where uncertainty is high
Signal and System Design for Wireless Power Transfer : Prototype, Experiment and Validation
A new line of research on communications and signals design for Wireless
Power Transfer (WPT) has recently emerged in the communication literature.
Promising signal strategies to maximize the power transfer efficiency of WPT
rely on (energy) beamforming, waveform, modulation and transmit diversity, and
a combination thereof. To a great extent, the study of those strategies has so
far been limited to theoretical performance analysis. In this paper, we study
the real over-the-air performance of all the aforementioned signal strategies
for WPT. To that end, we have designed, prototyped and experimented an
innovative radiative WPT architecture based on Software-Defined Radio (SDR)
that can operate in open-loop and closed-loop (with channel acquisition at the
transmitter) modes. The prototype consists of three important blocks, namely
the channel estimator, the signal generator, and the energy harvester. The
experiments have been conducted in a variety of deployments, including
frequency flat and frequency selective channels, under static and mobility
conditions. Experiments highlight that a channeladaptive WPT architecture based
on joint beamforming and waveform design offers significant performance
improvements in harvested DC power over conventional
single-antenna/multiantenna continuous wave systems. The experimental results
fully validate the observations predicted from the theoretical signal designs
and confirm the crucial and beneficial role played by the energy harvester
nonlinearity.Comment: Accepted to IEEE Transactions on Wireless Communication
Pilot Beam Sequence Design for Channel Estimation in Millimeter-Wave MIMO Systems: A POMDP Framework
In this paper, adaptive pilot beam sequence design for channel estimation in
large millimeter-wave (mmWave) MIMO systems is considered. By exploiting the
sparsity of mmWave MIMO channels with the virtual channel representation and
imposing a Markovian random walk assumption on the physical movement of the
line-of-sight (LOS) and reflection clusters, it is shown that the sparse
channel estimation problem in large mmWave MIMO systems reduces to a sequential
detection problem that finds the locations and values of the non-zero-valued
bins in a two-dimensional rectangular grid, and the optimal adaptive pilot
design problem can be cast into the framework of a partially observable Markov
decision process (POMDP). Under the POMDP framework, an optimal adaptive pilot
beam sequence design method is obtained to maximize the accumulated
transmission data rate for a given period of time. Numerical results are
provided to validate our pilot signal design method and they show that the
proposed method yields good performance.Comment: 6 pages, 6 figures, submitted to IEEE ICC 201
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