Providing quality of service guarantees in wireless LANs compliant with 802.11e

Quality of Service (QoS) support is a key attribute of a broadband communication system and is missing in 802.11-based wireless LANs. Recognizing the need, Task Group e (TGe) is work-ins! towards 802.11e, an evolution of the standard that provides the means for defining desirable QoS requirements for the traffic streams as well as a framework for scheduling schemes to achieve them. In this paper we propose a scheduling scheme for QoS guarantee provisioning that exploits and is fully compliant with the specifications of 802.11e. The scheduler operates at the access point and relies on the measurement and control parameters available in the fields of the 802.11e header to determine access during the evolution of PCF called HCF. Our scheme takes channel conditions under consideration in making these decisions, since information about the channel state can be conveyed now with the recent modifications adopted by TGh. Evaluation of our algorithm through simulation study shows significant performance improvement compared to earlier schemes that could not take channel conditions into consideration in making scheduling decisions. (C) 2004 Elsevier B.V. All rights reserved

Recommendations for quantitative uncertainty consideration in ecology and evolution

Ecological and evolutionary studies are currently failing to achieve complete and consistent reporting of model-related uncertainty. We identify three key barriers: a focus on parameter-related uncertainty, obscure uncertainty metrics, and limited recognition of uncertainty propagation, which have led to gaps in uncertainty consideration. But these gaps can be closed. We propose that uncertainty reporting in ecology and evolution can be improved through wider application of existing statistical solutions and adoption of good practice from other scientific fields. Our recommendations include greater consideration of input data and model structure uncertainties, field-specific uncertainty standards for methods and reporting, and increased uncertainty propagation through use of hierarchical models