Adaptation Techniques (adaptation + techniques)

Distribution by Scientific Domains

Selected Abstracts

Diversity and Adaptation of Shelters in Transitional Settlements for IDPs in Afghanistan

DISASTERS, Issue 4 2003
Joseph Ashmore
The diversity of shelters used in transitional settlements for internally displaced persons (IDPs) in Herat, Afghanistan is described. The information is based on a field survey undertaken in March 2002 and highlights the adaptation techniques, which IDPs undertake to improve any provided shelter. Potential areas for improvement are indicated; for example, the possibility for using insulated, demountable liners to prevent cold-related deaths without sacrificing shelter flexibility along with the likely need for better agency coordination of the shelter responses they provide. The wider context in which the technical recommendations would be implemented must also be considered. Such issues include agency resources, political impediments to providing the desired option, and the preference of many IDPs that the best shelter would be their home. [source]

Bayesian meta-modelling of engineering design simulations: a sequential approach with adaptation to irregularities in the response behaviour

A. Farhang-Mehr
Abstract Among current meta-modelling approaches, Bayesian-based interpolative methods have received significant attention in the literature. These methods are particularly known for their capability to adapt to the response function behaviour in order to generate good meta-models with fewer experiments. Current Bayesian adaptation techniques, however, are mainly based on the assumption that some variables are more important (or sensitive) than others. These less sensitive variables are weighted less or ignored to reduce the dimension of the design space. This assumption limits the scope and applicability of these models since in many practical cases none of the variables can be completely ignored or weighted less than others. This paper proposes a pragmatic approach that identifies regions of the design space where more experiments are needed based on the response function behaviour. The proposed approach adaptively utilizes the information obtained from previous experiments, builds interim meta-models, and identifies ,irregular' regions in which more experiments are needed. The behaviour of the interim meta-model is then quantified as a spatial function and incorporated into the next stage of the design to sequentially improve the accuracy of the obtained meta-model. The performance of the new approach is demonstrated using a numerical and an engineering example. Copyright 2005 John Wiley & Sons, Ltd. [source]

Adaptive coding and modulation for satellite broadband networks: From theory to practice

Hermann Bischl
Abstract This paper presents the detailed design and the key system performance results of a comprehensive laboratory demonstrator for a broadband Ka-band multi-beam satellite system exploiting the new DVB-S2 standard with adaptive coding and modulation (ACM). This complete demonstrator allows in-depth verification and optimization of the ACM techniques applied to large satellite broadband networks, as well as complementing and confirming the more theoretical or simulation-based findings published so far. It is demonstrated that few ACM configurations (in terms of modulation and coding) are able to efficiently cope with a typical Ka-band multi-beam satellite system with negligible capacity loss. It is also demonstrated that the exploitation of ACM thresholds with hysteresis represents the most reliable way to adapt the physical layer configuration to the spatial and time variability of the channel conditions while avoiding too many physical layer configuration changes. Simple ACM adaptation techniques, readily implementable over large-scale networks, are shown to perform very well, fulfilling the target packet-error rate requirements even in the presence of deep fading conditions. The impact of carrier phase noise and satellite nonlinearity has also been measured. Copyright 2009 John Wiley & Sons, Ltd. [source]

Channel estimation and physical layer adaptation techniques for satellite networks exploiting adaptive coding and modulation

Stefano Cioni
Abstract The exploitation of adaptive coding and modulation techniques for broadband multi-beam satellite communication networks operating at Ka-band and above has been shown to theoretically provide large system capacity gains. In this paper, the problem of how to accurately estimate the time-variant channel and how to adapt the physical layer taking into account the effects of estimator errors and (large) satellite propagation delays is analyzed, and practical solutions for both the forward and the reverse link are proposed. A novel pragmatic solution to the reverse link physical layer channel estimation in the presence of time-variant bursty interference has been devised. Physical layer adaptation algorithms jointly with design rules for hysteresis thresholds have been analytically derived. The imperfect physical layer channel estimation impact on the overall system capacity has been finally derived by means of an original semi-analytical approach. Through comprehensive system simulations for a realistic system study case, it is showed that the devised adaptation algorithms are able to successfully track critical Ka-band fading time series with a limited impact on the system capacity while satisfying the link outage probability requirement. Copyright 2008 John Wiley & Sons, Ltd. [source]