Walter Grote

Measurement and modeling of propagation losses in brick and concrete walls for the 900-MHz band

The prediction of wall losses is a fundamental aspect in the planning of cellular systems. The broad variety of building materials and construction codes makes accurate attenuation prediction very difficult without the support of specific construction data or measurements. In this paper, the attenuation and equivalent electric parameters /spl epsiv/ and /spl sigma/ of brick and doubly reinforced concrete walls are estimated for the 900-MHz band by fitting simple ray tracing models to empirical transmission data. The measurement setup is described, and extensive experimental results justifying the quasioptical modeling are presented.

Radio Communication Model for Underwater WSN

Underwater Wireless Sensor Networks (UWSN) experience severe communication problems due to large acoustic or electromagnetic (EM) signal attenuation. The propagation of acoustic signals in submarine media is possible with very low frequency signal carriers only, therefore reduced bandwidth, low transmission rates, thus extending transmission duration and diminishing battery life. Requirements to increase transmission data rates for UWSN have made it attractive to explore the possibilities of higher frequency EM transmissions. Recent experiments show that huge EM signal losses are to be expected in the near field of the transmitting antenna, however experiencing little additional reductions thereafter. The lack of a unified simple analytical model based on Maxwells equations that can be used as a design tool for these wireless submarine links, validated against published experimental results, is a problem that has been solved in this paper.

Indoor signal focusing by means of Fresnel zone plate lens attached to building wall

A simple inexpensive on-wall Fresnel zone plate (FZP) lens for indoor focusing of microwave signals is studied. It consists of concentric metal rings mounted on the outside of an exterior building wall. In our theoretical and empirical work the on-wall FZP lens is illuminated normally by a plane or spherical wave, of vertical or horizontal polarization, but other, more general incidence situations can be treated by similar means. The scalar quasi-optical focusing theory of the free-space zone plate has been modified and used for design and analysis of one-, two-, and three-ring on-wall FZP lenses. It is found that the presence of the wall does not change the FZP lens focusing efficiency significantly, but it has a strong axial defocusing effect. A 2-GHz FZP lens assembly consisting of three metal rings made out of thin antimosquito mesh has a focusing efficiency of about 15 dB (measured) and 14 dB (calculated), and axial defocusing of about 0.22 m. Some variations of on-wall/on-roof FZP lenses and their feasible applications in the microwave/millimeter-wave communication links are also discussed.

Wood moisture content measurement at 2.45 GHz

Wood, being one of the most widely used construction materials by industry, relies on its moisture content for strength, durability and ductility. Lumber industry has long been searching for a non-destructive, accurate and fast method to determine moisture content in wood to replace the traditional one based on weighing. This paper evaluates the performance of a 2.45 GHz measuring system that determines moisture content of 4 cm thick wood samples. If dry wood and water densities are defined as the ratio between their masses and the volume of the wood sample, then they can be estimated by establishing the attenuation, phase shift and depolarization of the electromagnetic wave that propagates through the wood. Using this technique, moisture content of Radiata pine tree boards in the range of 0 to 68% has been established, with dry wood density ranging from 390 to 530 Kg/m3 and water density from 0 to 285 Kg/m3. This is an improvement of 2.4 times of previously reported measurements.

Key dependent cipher scheme for sensor networks

Wireless Sensor Networks (WSN) are a promising future for many commercial and military applications. WSN is vulnerable to a variety of potential attacks (active and passive). The confidentiality of WSN is an essential service and becoming a major concern for security WSN protocol designers. However, the characteristics of WSN (limitations of power, computation and memory) impose security challenges, since the conventional ciphers suffer from these limitations. In this paper, a new different cipher technique is defined to ensure the data confidentiality with a significant reduction of computational complexity, energy cost, and communication overhead. The proposed cipher is applied on a set of packets called generation. The strength of the proposed cipher against attacks is based on its dynamic property. The basic scheme was tested and evaluated by comparing it with Advanced Encryption Standard (AES) algorithm, which is considered as a reliable and robust cipher algorithm. Theoretical and simulation results of the proposed cipher scheme show that it is immune against linear, differential, chosen/known-plain-text, brute force, and statistical attacks.

Performance Analysis of Slotted CSMA/CA IEEE 802.15.4 with Heterogeneous No-Acknowledged Uplink Traffic

IEEE 802.15.4 Wireless Sensor Networks (WSN) often are used in cluster topologies, where one or more reduced function devices (RFD) exchange messages with full function devices (FFD). FFDs, in turn, may exchange messages among themselves in a tree topology. To be energy efficient, these devices will collect received messages and regroup them in order to reduce the protocol overhead associated to communications. As a result, WSN messages may differ in size and periodicity, a fact that has not been studied in performance analysis of this kind of networks. An analytical model that considers variable message size, transmission scheduling and the impact of these on energy consumption is presented and then validated by simulations.

Wireless SISO Channel Propagation Model for Underground Mines

Abstract Modern mining procedures aim to replace human resources directly involved in the mineral extraction process by automatic or remote control systems. Data may be collected from sensors, or data and/or video may be transmitted by telecommunication equipment. The actual technology trend is to do these transmissions using wireless technology (WSN, Wi-Fi, among others). This work summarizes the experience that has been collected from characterizing a Single-Input-Single-Output (SISO) large scale 870 MHz and 2.45 GHz wireless propagation channel in an underground copper mine. Also the Rician K factor and channel coherence time are calculated for a 2.45 GHz mobile link.

IEEE 802.11 Goodput Analysis for Mixed Real Time and Data Traffic

An IEEE 802.11 analytical performance evaluation model for ad-hoc WLAN’s comprising terminals with different traffic source characteristics is presented. Although some publications address this issue, most of them propose to modify the original standard by some means that will affect the probability of transmission of a device when the network reaches congestion. The approach of this publication is to be able to establish a set of equations such that an intelligent choice of configuration parameters of standard home devices may improve the performance of the wireless network. Actually, two models are presented and compared, a simple one based on stationary behavior of the network assuming collisions have a negligible effect on network performance, and a second model based on a stationary stochastic model of a network, where devices have a packet ready for transmission at all times.

Home networking: performance and architecture challenges

Home networking is a developing area of research in telecommunications. The historical development of this sector has been shifting from node to network backbone design, and more recently, to access technologies, that is, from the core to the periphery of the network. One of the important problems being addressed nowadays is the so called “last mile” connectivity. A number of recent technologies—like WiMAX, xDSL, and Fiber To the Home—have been developed to meet this challenge. Solutions of this kind are making it possible to bring broadband connections to companies, business, and homes. What is left is the so called “last meter” problem and this is one of the areas where home networking will play an important role. True telecommuting will only be possible with present day technologies if broadband connections are made possible up to the application-oriented device. This also opens the possibilities to include new and existing devices that in the past were not being considered as part of the network. Small electronic devices are taking part of our everyday life and change our habitat so that we may optimize the way we fulfil all our daily tasks. Communications between those devices are complex since they deal with scalability, privacy, energy consumption, and new applications. The authors of those papers that were selected from among the papers presented at the IFIP Home Networking Conference held in December 2007 in Paris, France, were invited to submit their full papers after possible extension, and we received ten papers. It is our great regret that although all the submitted papers were of high quality, only five of them were accepted after a careful review due to technical constraints of the journal. In the first paper, Anna Pizzinat, Franck Payoux, Benoît Charbonnier, and Sylvain Meyer explore a new architecture that permits to extend the high bit coverage area in UWB standard using radiofrequency to optical signal transceivers and optical fibers. They show by means of analysis, simulation, and measurements that in spite of high attenuations to be expected from the high frequency use of UWB, it is possible to provide full network coverage in indoor environments. This offers excellent possibilities for new home networking services that need gigabit per second transmission rates. Walter Grote, Alex Grote, and Isabel Delgado present a performance analysis to study the goodput of Wi-Fi-based home networks for mixed traffic. Two different analytical models are proposed and compared to each other, validating one of them by means of simulation. By applying these models, significant improvements on goodput can be obtained by changing configurable parameters of present day mobile devices. The third paper of this collection, presented by Helmut Hlavacs, Roman Weidlich, Karin A. Hummel, Amine M. Houyou, Andreas Berl, and Hermann de Meer proposes a new architecture that achieves a distributed energy allocation by sharing computational resources in home environAnn. Telecommun. (2008) 63:453–454 DOI 10.1007/s12243-008-0051-4