Search results for "Communications system"
showing 10 items of 78 documents
Automated Soil Moisture Monitoring Wireless Sensor Network for Long-Term Cal/Val Applications
2012
The design and development of a wireless sensor network for soil moisture measurement in an unlevelled 10 km × 10 km area, is described. It was specifically deployed for the characterization of a reference area, in campaigns of calibration and validation of the space mission SMOS (Soil Moisture and Ocean Salinity), but the system is easily extensible to monitor other climatic or environmental variables, as well as to other regions of ecological interest. The network consists of a number of automatic measurement stations, strategically placed following soil homogeneity and land uses criteria. Every station includes acquisition, conditioning and communication systems. The electronics are batt…
Energy Harvesting Powered Packet Transmissions in Duty-Cycled WSNs: A DTMC Analysis
2017
Energy harvesting (EH) promises an extended lifetime for wireless sensor networks (WSNs), supplying sensor nodes with accumulated energy from natural sources. Different from battery powered sensors, nodes in EH-enabled WSNs are equipped with an energy harvesting accessory in order to extract energy from surrounding sources. Based upon the harvested energy, sensor nodes perform data exchange activities. In this paper, we develop two discrete time Markov chain (DTMC) models to analyze the performance of packet transmissions in such a WSN while employing a generic synchronous medium access control (MAC) protocol. Using the proposed DTMC models, we investigate the effect of EH over a specific s…
Energy Efficient Consecutive Packet Transmissions in Receiver-Initiated Wake-Up Radio Enabled WSNs
2018
In wake-up radio (WuR)-enabled wireless sensor networks, data communication among nodes is triggered in an on-demand manner, by either a sender or a receiver. For receiver-initiated WuR (RI-WuR), a receiving node wakes up sending nodes through a wake-up call. Correspondingly sending nodes transmit packets in a traditional way by competing with one another multiple times in a single operational cycle. In this paper, we propose a receiver-initiated consecutive packet transmission WuR (RI-CPT-WuR) medium access control (MAC) protocol, which eliminates multiple competitions to achieve higher energy efficiency. Furthermore, we develop two associated discrete time Markov chains (DTMCs) for evalua…
A New Iterative Procedure for the Localization of a Moving Object/Person in Indoor Areas from Received RF Signals
2019
This paper presents a new iterative estimation method to localize a single moving object or person in non-stationary 3-dimensional (3D) indoor environments from received radiofrequency (RF) signals. The moving object/person is modelled by a moving single point scatterer. The indoor space is equipped with a multiple-input multiple-output (MIMO) communication system. This work starts by introducing a new geometrical channel model which considers the effects of the line-of-sight (LOS) component, the fixed objects located in a room, and the moving object (point scatterer). Then, we present an iterative estimation technique for computing the time-variant (TV) coordinates of the moving scatterer.…
Power allocation optimization in OFDM-based cognitive radios based on sensing information
2011
Owing to the non-zero probability of the missed detection and false alarm of active primary transmission, a certain degree of performance degradation of the primary user (PU) from cognitive radio users (CRs) is unavoidable. In this paper, we consider OFDM-based communication systems and present efficient algorithms to maximize the total rate of the CR by optimizing jointly both the detection operation and the power allocation, taking into account the influence of the probabilities of missed detection and false alarm, namely, the sensing accuracy. The optimization problem can be formulated as a two-variable non-convex problem, which can be solved approximately by using an alternating directi…
A wideband multiple-cluster MIMO mobile-to-mobile channel model based on the geometrical street model
2008
In this paper, we extend the geometrical street multiple-input multiple-output (MIMO) mobile-to-mobile (M2M) channel model with respect to multiple clusters of scatterers as well as to frequency selectivity. The statistical properties of the proposed reference model are studied. Analytical solutions are provided for the three-dimensional (3D) space-time cross-correlation function (CCF), the temporal autocorrelation function (ACF), the 2D space CCF, and the frequency correlation function (FCF). The correlation properties are studied under the assumption of non-isotropic scattering conditions. The proposed reference model can be used as a starting point for the derivation of a wideband MIMO M…
A narrowband MIMO car-to-car channel model based on the geometrical street scattering model
2012
In this paper, we model a narrowband multiple-input multiple-output (MIMO) car-to-car (C2C) channel model based on the geometrical street scattering model. Starting from the geometrical model, a MIMO reference channel model is derived under the assumption of single-bounce scattering in line-of-sight (LOS) and non-LOS (NLOS) propagation environments. In the proposed channel model, an infinite number of scatterers are uniformly distributed in rectangular grids located on both sides of the street. Analytical solutions are presented for the three-dimensional (3D) space-time cross-correlation function (CCF), the temporal autocorrelation function (ACF), and the two-dimensional (2D) space CCF. An …
Effectiveness of Safety Warnings in Atypical Antipsychotic Drugs
2009
Studies conducted to obtain drug authorization are often of short duration and based on small sample sizes in selected populations. Policies on drug safety rely on the validity of the methods used to achieve rapid and effective communication of new information. No formal evaluation has ever been made of the Spanish communications system, although indirect data have raised questions about its effectiveness.To evaluate the impact of two safety warnings issued by the Spanish Drug Agency, and of a later prior authorization requirement involving the use of atypical antipsychotic drugs in the elderly.The study was based on a time-series analysis constructed with data corresponding to monthly invo…
An agenda model of organisational communication
2001
The purpose of the study is to analyse the meanings and valuations the members of a working organisation attach to organisational communication and to construct them into a model of meanings of organisational communication. The result is the agenda model of organisational communication. The model shows that members of a working organisation see the communication culture construct from four dimensions of meaning. The dimensions are: the use of the communication system, superior communication and ways of conduct, horizontal face‐to‐face communication and the functioning of the communication process. The agenda model is a new kind of method to get the information needed for the planning and de…
A secure architecture for P2PSIP-based communication systems
2009
Today, Peer-to-Peer SIP based communication systems have attracted much attention from both academia and industry. The decentralized nature of P2P might provide the distributed peer-to-peer communication system without help of the traditional SIP server. However, it comes to the cost of reduced manageability and therefore causes security problems, e.g. distrust, privacy leaks, unpredictable availability, etc. In this paper, we investigate on P2PSIP security issues and propose a proxy-based system architecture that improves security during P2PSIP session initiation. The main issues considered in this architecture include Source inter-working, Encryption & Decryption, Policy Management, Desti…