Sparse multiple relay selection for network beamforming with individual power constraints using semidefinite relaxation

This paper deals with the multiple relay selection problem in two-hop wireless cooperative networks with individual power constraints at the relays. In particular, it addresses the problem of selecting the best subset of K cooperative nodes and their corresponding beamforming weights so that the signal-to-noise ratio (SNR) is maximized at the destination. This problem is computationally demanding and requires an exhaustive search over all the possible combinations. In order to reduce the complexity, a new suboptimal method is proposed. This technique exhibits a near-optimal performance with a computational burden that is far less than the one needed in the combinatorial search. The proposed method is based on the use of the l1-norm squared and the Charnes-Cooper transformation and naturally leads to a semidefinite programming relaxation with an affordable computational cost. Contrary to other approaches in the literature, the technique exposed herein is based on the knowledge of the second-order statistics of the channels and the relays are not limited to cooperate with full power.Peer ReviewedPostprint (author's final draft

Relay subset selection in cognitive networks with imperfect CSI and individual power constraints

This paper considers the relay subset selection problem in an underlay cognitive network in which two secondary users communicate assisted by a set of N potential relays. More specifically, this paper deals with the joint problem of choosing the best subset of L secondary relays and their corresponding weights which maximize the Signal-to-Interference-plus-Noise ratio (SINR) at the secondary user receiver, subject to per-relay power constraints and interference power constraints at the primary user. This problem is a combinatorial problem with a high computational burden. Nevertheless, we propose a sub-optimal technique, based on a convex relaxation of the problem, which achieves a near-optimal performance with a reduced complexity. Contrary to other approaches in the literature, the secondary relays are not limited to cooperate at full power.Peer ReviewedPostprint (author's final draft

Finite State Machine Synthesis for Evolutionary Hardware

This article considers application of genetic algorithms for finite machine synthesis. The resulting genetic finite state machines synthesis algorithm allows for creation of machines with less number of states and within shorter time. This makes it possible to use hardware-oriented genetic finite machines synthesis algorithm in autonomous systems on reconfigurable platforms

Farmers' Use of Improved Seed Selection Practices in Mexican Maize: Evidence and Issues from the Sierra de Santa Marta

The principal advantage of in situ conservation is that it allows adaptive evolutionary processes to continue in the species that are being conserved. For a cultivated crop species, in situ conservation involves farmers' management of their own genetic resources even as the farmers themselves adapt to a changing environment. Improved seed selection practices and other on-farm breeding strategies have been proposed as a means of providing economic incentives for farmers to continue growing traditional varieties or landraces identified as important for conservation. This paper describes a pilot study among a group of indigenous farmers in the Sierra de Santa Marta, Veracruz, Mexico, who have collaborated in such efforts. The findings raise key issues about the potential impact of such an approach, as well as some useful methodological points for applied economists. In the study area, there is a high frequency of experimentation, exchange, loss, and replacement of seed over time -- seed of the same varieties, including both modern and traditional varieties. This poses a challenge for economists' models of varietal choice, which tend to be based on static perceptions of a 'variety' as well as simplistic distinctions between 'modern' and 'traditional' varieties. Seed selection in the study area is not a single event but an iterative, continuous process. Women may be more involved in seed selection than previously thought, which may have implications for the welfare impact of new seed selection practices. Other implications of the study are that (1) the impact of introducing practices to enhance farmers' varieties is likely to be diffuse and difficult to observe, predict, or measure, and (2) in developing analytical models of farmer decision-making as it affects the diversity of genetic resources on the farm, the most appropriate unit of analysis for predicting the effects of some policy interventions is not likely to be the individual farmer or the individual farm household. A better understanding of the 'social infrastructure' shaping seed and information flows is needed, since in the diffusion of innovations of this type, the seed system is based entirely on farmers and their interactions.Crop Production/Industries,

Notas sobre las proporciones del cuerpo humano según Vitruvio y San Agustín

Notas sobre las proporciones del cuerpo humano según Vitruvio y San Agustí

Eero Saarinem

Eero Saarine

Las Escuelas Pías de San Antón de Madrid

Las Escuelas Pías de San Antón de Madri

Actuación en zonas antiguas de pueblos y ciudades

Actuación en zonas antiguas de pueblos y ciudade

Eugenio d'Ors

Eugenio d'Or

Alrededor de Hipódamo de Mileto. Comentarios sobre la trilogía de Luis Cervera Vera

Alrededor de Hipódamo de Mileto. Comentarios sobre la trilogía de Luis Cervera Ver