Search results for "working"
showing 10 items of 2747 documents
Simultaneous ranging and self-positioning in unsynchronized wireless acoustic sensor networks
2016
Automatic ranging and self-positioning is a very desirable property in wireless acoustic sensor networks, where nodes have at least one microphone and one loudspeaker. However, due to environmental noise, interference, and multipath effects, audio-based ranging is a challenging task. This paper presents a fast ranging and positioning strategy that makes use of the correlation properties of pseudonoise sequences for estimating simultaneously relative time-of-arrivals from multiple acoustic nodes. To this end, a proper test signal design adapted to the acoustic node transducers is proposed. In addition, a novel self-interference reduction method and a peak matching algorithm are introduced, a…
Measurement and Modeling of the Origins of Starvation of Congestion-Controlled Flows in Wireless Mesh Networks
2009
Significant progress has been made in understanding the behavior of TCP and congestion-controlled traffic over CSMA-based multihop wireless networks. Despite these advances, however, no prior work identified severe throughput imbalances in the basic scenario of mesh networks, in which a one-hop flow contends with a two-hop flow for gateway access. In this paper, we demonstrate via real network measurements, testbed experiments, and an analytical model that starvation exists in such a scenario; i.e., the one-hop flow receives most of the bandwidth, while the two-hop flow starves. Our analytical model yields a solution consisting of a simple contention window policy that can be implemented vi…
Testbed implementation of the meta-MAC protocol
2016
The meta-MAC protocol is a systematic and automatic method to dynamically combine any set of existing MAC protocols into a single higher layer MAC protocol. We present a proof-of-concept implementation of the meta-MAC protocol by utilizing a programmable wireless MAC processor (WMP) on top of a commodity wireless card in combination with a host-level software module. The implementation allows us to combine, with certain constraints, a number of protocols each represented as an extended finite state machine. To illustrate the combination principle, we combine protocols of the same type but with varying parameters in a wireless mesh network. Specifically, we combine TDMA protocols with all po…
Experimental characterization and mitigation of turbulence induced signal fades within an ad hoc FSO network
2014
Optical beams propagating through the turbulent atmospheric channel suffer from both the attenuation and phase distortion. Since future wireless networks are envisaged to be deployed in the ad hoc mesh topology, this paper presents the experimental laboratory characterization of mitigation of turbulence induced signal fades for two ad hoc scenarios. Results from measurements of the thermal structure constant along the propagation channels, changes of the coherence lengths for different turbulence regimes and the eye diagrams for partially correlated turbulences in free space optical channels are discussed. Based on these results future deployment of optical ad hoc networks can be more strai…
Significance of channel failures on network performance in CRNs with reserved spectrum
2016
It is well understood that in wireless networks, channel failures, which are typically caused by equipment or power failures as well as intrinsic features in radio transmissions, such as fading and shadowing, can easily result in network performance degradation. Therefore, fast recovery from channel failures is an important measure that should be incorporated with those networks. Consequently, in a cognitive radio network (CRN), channel failures can cause significant performance degradation in both primary and secondary networks. Instead, retainability, i.e., the capability of providing continuous connection for users must be guaranteed even if a significant network element is disrupted. In…
Making WiFi work in multi-hop topologies: Automatic negotiation and allocation of airtime
2015
We propose a solution for mitigating the performance impairments of CSMA/CA protocols in multi-hop topologies based on the dynamic adaptation of the contention process experienced by nodes in a wireless network. A distributed protocol is used to negotiate the channel airtime for a node as a function of the traffic requirements of its neighbourhood, taking into account bandwidth reserved for the control operations. A mechanism is provided for a node to tune its contention window depending on its allocated airtime. Different from previous schemes, a node's contention window is fixed in size unless the traffic requirements of its neighbourhood change. The scheme is implemented on legacy commer…
On the Reception of Grassmann’s Work in Germany during the 1870’s
1996
It has often been remarked that Grassmann’s mathematics was not widely appreciated during his lifetime. Although awareness of the dimensions of his achievements began to spread in the early 1870’s, even in Germany relatively few mathematicians appear to have been well acquainted with either the original 1844 edition of Grassmann’s Ausdehnungslehre or the mathematically more accessible edition of 1862. The main reasons for this weak and rather delayed reception have been described often enough---Grassmann’s isolated working environment and his nearly impenetrable language---but there are a number of related aspects that still deserve closer consideration.1
Tiheä, tavallinen ja joustava
2012
Combining work with family life is a topical and socially important question. This article examines how under-40-year old female PhD students with a family manage to combine the roles of a mother and a doctoral student in their everyday life and how they deal with the major and simultaneous challenges these roles bring. The focus is on the everyday challenges female PhD students face and the choices they have to make at the interface of family and study. This article is part of research examining the life course and future thinking of female PhD students. Nowadays the atmosphere of planning is all-pervasive. Individuals are expected to plan their life course carefully. They should plan thei…
CREATING A POSITIVE WORKING ENVIRONMENT FOR TEACHERS
2018
The purpose of the research paper is to study a positive working environment importance for teachers work satisfaction and the role of principal in improving working conditions. Whereas teacher profession is subject to different changes and reforms it makes the whole profession and teacher well-being an important subject to discuss.The research paper includes analysis of the theoretical material about physical environment as well as psychological (also called microclimate). Empirical part is based on teacher’s survey – 97 teachers from different schools in Riga were involved. The statements of survey have partially adopted from Teaching and Learning International Study TALIS 2013. The main …
Tentative Reflections on Construction of Assessment Models for Buildings’ Sustainability Certification
2017
All over the word several rating systems have been produced to certificate the sustainability level of buildings. Experts agree on considering sustainability a typical field for multicriteria decision analysis, but buildings’ rating systems do not comply in a consistent manner this assessment approach. Proposals for using classical and hybrid ranking procedures are aimed to quantify the relative attractiveness of buildings, but do not give information on their absolute attractiveness. While several studies propose suitable application of multicriteria decision making techniques for assessing buildings’ sustainability with the purpose of choosing the best solution or obtaining a ranking on a…