Mobility Impact on Cluster Based MAC Layer Protocols in Wireless Sensor Networks

Wireless sensor networks (WSNs) enable a wide variety of applications resulting in still increasing requirements for the protocols supporting the operations. The medium access control (MAC) layer protocols are essential for improving the performance of an application and its quality of service because MAC protocols influence channel capacity utilization, network delay, energy consumption, and scalability. The contribution of this paper is two novel cluster-based time division multiple access (TDMA) scheduling MACs for WSNs and an analysis of the mobility impact on both. The proposed MAC layer protocols support real time applications where the cluster-based scheduling improves the scalability and also improves the performance in varying network conditions. The paper presents the design, implementation and performance evaluation of the proposed cluster based TDMA scheduling algorithms green conflict free (GCF) and multicolor-GCF (M-GCF) for high complexity and high requirement applications of WSNs under both low and high mobility conditions. The comparative evaluation shows that the M-GCF algorithm has better slot sharing and less conflicts with reduced communication energy consumption, delay, and good throughput under static and low mobility conditions while the GCF algorithm has better performance in high mobility scenarios. The paper also defines the mobility threshold that decides the use of the GCF- and M-GCF algorithms according to the mobility requirement of application.     

Room electromagnetics

In analogy with the established discipline of room acoustics, various aspects of diffuse wideband microwave propagation in a room are treated. It is shown that an equivalent to Sabine's equation for reverberation time in a room is valid for the completely diffused field, depending only on the volume, the surface area, and an effective absorption coefficient. An exponential decay of the power as a function of the delay is a consequence of the assumptions. Furthermore, the concept of a reverberation distance is also valid. This is the distance from a transmitting antenna where the received diffuse, randomly scattered power equals the direct line-of-sight received power, such that the diffuse power dominates for distances larger than the reverberation distance. A number of measurements in a large room support the theory with an effective absorption coefficient of 0.5. The power delay profiles around the room from a transmitter in the ceiling vary only in the first arriving part of the impulse, whereas the tail, being dominated by the diffuse field, has the same power level for a given delay and the same decay rate all over the room. It is also a consequence of the theory that the diffuse fields incident on an antenna are uniformly distributed in angle.     

A Transmitter Architecture Based on Delta–Sigma Modulation and Switch-Mode Power Amplification

This brief presents a method of deploying RF switch-mode power amplification for varying envelope signals. Thereby the power amplifier can be operated as a switch with a high power efficiency as the result. The key idea is to transmit either a full RF period or none at all in such a way that the correct modulated RF signal is obtained after filtering. This is accomplished in a novel configuration of a low-pass DeltaSigma modulator using a phase modulated clock combined with a simple AND-gate. The designed modulator is easy to implement, displays very good linearity and offers time domain signals that promote the power efficiency of the power amplifier. The working principle is described through theory and simulations, and validation is done via measurements on a prototype of the modulator. Measurements on the prototype show that the presented modulator modulates a UMTS signal with more than 10-dB margin to the spectrum mask and EVM below 0.85% RMS (req<17.5%). Delta-sigma, power amplifier (PA), RF, switch mode, transmitter architecture, varying envelope.     

Demonstration of multi-core photonic crystal fibre in an optical interconnect

A novel microstructured fibre has been created for use in an optical interconnection system. The fibre has low crosstalk with a high density of cores corresponding to 1150 channels/mm/sup 2/. A repeating pseudorandom binary sequence has been used to demonstrate a four-channel transmit/receive system using vertical cavity surface emitting lasers as both emitters and detectors.     

On the benefits of location-based relay selection in mobile wireless networks

We consider infrastructure-based mobile networks that are assisted by a single relay transmission where both the downstream destination and relay nodes are mobile. Selecting the optimal transmission path for a destination node requires up-to-date link quality estimates of all relevant links. If the relay selection is based on link quality measurements, the number of links to update grows quadratically with the number of nodes, and measurements need to be updated frequently when nodes are mobile. In this paper, we consider a location-based relay selection scheme where link qualities are estimated from node positions; in the scenario of a node-based location system such as GPS, the location-based approach reduces signaling overhead, which in this case only grows linearly with the number of nodes. This paper studies these two relay selection approaches and investigates how they are affected with varying information update interval, node mobility, location inaccuracy, and inaccurate propagation model parameters. Our results show that location-based relay selection performs better than SNR-based relay selection at typical levels of location error when medium-scale fading can be neglected or accurately predicted.     

Optimal Sampling and Processing of an Impulse Radio Signal Subjected to Narrow Band Interference

In this paper the sampling, quantization and processing of an ultra-wideband (UWB) impulse radio (IR) receiver signal is considered when the propagation link is subjected to additive white Gaussian noise (AWGN) and narrow band interference (NBI) which may be non-Gaussian. The Neyman Pearson log likelihood ratio formulation results in receiver processing that consists of a Generalized Matched Filter (GMF) and linear sampling which exploits the correlation of the NBI noise to effectively suppress it. However, the processing requirements to implement the GMF are prohibitive in the context of an UWB IR. Hence an alternate highly efficient processing scheme based on crude 2 and 3 level quantization with maximum ratio combining (MRC) Rake processing is considered and analyzed. As demonstrated in this paper, the 3 level quantizer is an excellent compromise between receiver performance and computational efficiency and can in some cases exceed the performance of a comparable Rake receiver using linear sampling. This happens in some practical instances when the noise is non-gaussian as will be demonstrated. John Nielsen obtained his BASc and MSc from the University of Toronto in 1981 and 1983 respectively and his PhD from the University of Ottawa in 1990. He became a faculty member of the Department of Electrical and Computer Engineering of the University of Calgary in 2002 as an Associate Professor. He is also an affiliated researcher with Telecommunications Research Laboratory of Calgary. His primary research interests are in physical layer wireless communication systems. Prior to his faculty position, Dr. Nielsen was with Research in Motion and Nortel.     

Automated effect-specific mammographic pattern measures

We investigate the possibility to develop methodologies for assessing effect specific structural changes of the breast tissue using a general statistical machine learning framework. We present an approach of obtaining objective mammographic pattern measures quantifying a specific biological effect, such as hormone replacement therapy (HRT). We compare results using this approach to using standard density measures. We show that the proposed method can quantify both age related effects and effects caused by HRT. Age effects are significantly detected by our method where standard methodologies fail. The separation of HRT subpopulations using our approach is comparable to the best methodology, which is interactive.      

Determination of length changes due to moisture variations in autoclaved aerated concrete

Length changes of autoclaved aerated concrete due to moisture variations have been investigated by tests on a Danish brand of autoclaved aerated concrete. The investigation have shown that autoclaved aerated concrete with delivery moisture content exhibits swelling when initially conditioned at relative humidities above 43%, whereas initial conditioning below 43% relative humidity leads to shrinkage. After the initial conditioning has been performed, length changes are shown to be almost proportional to the variation in relative humidity. The investigation has shown that the present Danish Standard in this area is misleading, and the principle of a new NORDTEST method, NT Build 444(1996), is presented, Furthermore this test method is compared with the European Standard EN 680,Determination of the drying shrinkage of autoclaved aerated concrete, and a draft for another European Standard prEN 772-12:1992,Determination of length change during moisture movements in autoclaved aerated concrete masonry units.     

Prevalence and diversity of Campylobacter jejuni in pig herds on farms with and without cattle or poultry

The prevalence and diversity of Campylobacter jejuni was investigated in pig herds on farms with and without cattle or poultry production. A bacteriological screening of pig cecal samples from 247 finisher herds was carried out at the slaughter-house. Subsequently, a follow-up study was conducted in 24 herds (either with or without prior C. jejuni isolation from pigs) in which fecal samples were collected from pigs and, if present, cattle and poultry. Samples were analyzed for presence of Campylobacter, and subsequent analysis included species identification, serotyping, and, for selected strains, pulsed-field gel electrophoresis typing. In the slaughterhouse screening, C. jejuni was isolated from pigs in 21 (8.5%) herds, but no significant difference in prevalence was found between herd types (pigs, pigs and cattle, pigs and poultry). At the slaughterhouse, C. jejuni and Campylobacter coli prevalence in pigs was 2.3 and 90.1%, respectively. In the follow-up study, herd prevalence of C. jejuni was 8.3%, whereas C. jejuni and C. coli were isolated from 0.8 and 92.0% of pigs, respectively. In mixed production herds, C. jejuni predominated in cattle (42.7%) and poultry (31.6%), whereas C. jejuni was only isolated from 1.3 to 2.5% of pigs in these herds. There were no significant differences in C. jejuni or C. coli prevalence in pigs, cattle, and poultry between herds with and without prior C. jejuni isolation at the slaughterhouse. Pulsed-field gel electrophoresis typing did not yield evidence of C. jejuni transmission between cattle or poultry and pigs in mixed production herds. In contrast, pulsed-field gel electrophoresis analysis showed indistinguishable serotypes of C. coli in pigs and cattle in two herds. Verification of C. jejuni-positive pig samples showed that individual pigs can excrete high levels of C. jejuni and that mixed infection with C. jejuni and C. coli was common in C. jejuni-positive pigs. The results of our study suggest that transmission of C. jejuni between pigs and cattle or poultry in mixed production herds occurs infrequently. Detection of indistinguishable C. coli isolates in two herds, however, might indicate the existence of low-level transmission between pigs and cattle in herds of mixed production.