David Ndzi

Vegetation attenuation measurements and modeling in plantations for wireless sensor network planning

As wireless communication moves from long to short ranges with considerably lower antenna heights, the need to understand and be able to predict the impact of vegetation on coverage and quality of wireless services has become very important. This paper focuses on vegetation attenuation measurements for frequencies in the range 0.4{7.2GHz in mango and oil palm plantations to evaluate vegetation attenuation models for application in wireless sensor network planning and deployment in precision agriculture. Although a number of models have been proposed and evaluated for speciflc frequencies, results show that these models do not perform well when applied to difierent vegetation types or at difierent frequencies. A global assessment of the models using a broad range of frequencies shows that the COST 235 model gives more consistent results when there is vegetation in the propagation path. For grid-like plantation, the study shows that the RET model provides the best prediction of path loss for measurements between two rows of trees. However, taking into account

A robotic welding system using image processing techniques and a CAD model to provide information to a multi‐intelligent decision module

Purpose – The paper aims to propose a system that uses a combination of techniques to suggest weld requirements for ships parts. These suggestions are evaluated, decisions are made and then weld parameters are sent to a program generator.Design/methodology/approach – A pattern recognition system recognizes shipbuilding parts using shape contour information. Fourier‐descriptors provide information and neural networks make decisions about shapes.Findings – The system has distinguished between various parts and programs have been generated so that the methods have proved to be valid approaches.Practical implications – The new system used a rudimentary curvature metric that measured Euclidean distance between two points in a window but the improved accuracy and ease of implementation can benefit other applications concerning curve approximation, node tracing, and image processing, but especially in identifying images of manufactured parts with distinct corners.Originality/value – A new proposed system has bee...

The study of human movement effect on Signal Strength for indoor WSN deployment

This paper proposes the use of a wireless sensor network (WSN) as a passive human behavior monitoring system for enabling intelligent green building. The proposed application required further investigation and study of the effect of human movement on wireless signals at 2.4GHz. It is important to understand the significant effect caused by human movement on the Received Signal Strength Indicator (RSSI). Several experiments are conducted using WSN mote from MEMSIC to obtain wireless attenuation models based on the number of people and movement speed. Prior to the experiments, the co-existence of different systems in the 2.4GHz frequency band is measured to select unoccupied IEEE802.15.4 channel to prevent co-channel interferences. Results show that the presence of people moving in indoor significantly affects the RSSI and the attenuation varies with the number of people and their movement speed. The attenuation model of human movement in indoor environment has enabled the use of existing WSN in the building to detect the presence of people and act as a passive sensor for human movement to enable effective lighting and air-conditioning control system.

Analysis of successes and failures with a tele-operated mobile robot in various modes of operation

The effect on failure rates of the way tele-operators interact with mobile robots is investigated. Human tele-operators attempted to move a robot through progressively more complicated environments with reducing gaps, as quickly as possible. Tele-operators used a joystick and either watched robots, while operating them, or used a computer screen to view scenes remotely. Cameras were either mounted on the robot to view the space ahead of the robot or mounted remotely so that they viewed both the environment and robot. Tele-operators completed tests both with and without sensors. Both an umbilical cable and a radio link were used.

Signal propagation in aquaculture environment for wireless sensor network applications

This paper presents results of signal propagation studies for wireless sensor network planning in aquaculture environment for water quality and changes in water characteristics monitoring. Some water pollutants can cause widespread damage to marine life within a very short time period and thus wireless sensor network reliability is more critical than in crop farming. This paper shows that network coverage models and assumptions over land do not readily apply in tropical aquaculture environment where high temperatures are experienced during the day. More speci¯cally, due to high humidity caused by evaporation, network coverage at 15 cm antenna height is better than at 5m antenna heights due to the presence of a super-refraction (ducting) layer. For a 69m link, the di®erence between the signal strength measured over several days is more than 7dBm except under anomaly conditions. In this environment, the two-ray model has been found to provide high accuracy for signal propagation over water where there are no objects in close proximity to the propagation path. However, with vegetation in close proximity, accurate signal variation predication must consider contributions from scattered and diffused components, taking into account frequency selective fading characteristics to represent the temporal and spatial signal variations.

Signal Propagation Analysis for Low Data Rate Wireless Sensor Network Applications in Sport Grounds and on Roads

This paper presents results of a study to characterise wire-less point-to-point channel for wireless sensor networks applications in sport hard court arenas, grass fields and on roads. Antenna height and orientation effects on coverage are also studied and results show that for omni-directional patch antenna, node range is reduced by a factor of 2 when the antenna orientation is changed from vertical to horizontal. The maximum range for a wireless node on a hard court sport arena has been determined to be 70m for 0dBm transmission but this reduces to 60m on a road surface and to 50m on a grass field. For horizontal antenna orientation the range on the road is longer than on the sport court which shows that scattered signal components from the rougher road surface combine to extend the communication range. The channels investigated showed that packet error ratio (PER) is dominated by large-scale, rather than small-scale, channel fading with an abrupt transition from low PER to 100% PER. Results also show that large-scale received signal power can be modelled with a 2nd order log-distance polynomial equation on the sport court and road, but a 1st order model is sufficient for the grass field. Small-scale signal variations have been found to have a Rice distribution for signal to noise ratio levels greater than 10 dB but the Rice K-factor exhibits significant variations at short distances which can be attributed to the influence of strong ground reflections.

A new RREQ message forwarding technique based on Bayesian probability theory

The flooding method, which is used by many mobile ad-hoc routing protocols, is a process in which a route request packet (RREQ) is broadcasted from a source node to other nodes in the network. This often results in unnecessary re-transmissions, causing packet collisions and congestion in the network, a phenomenon called broadcast storm. This article presents firstly the impact of a different message forwarding probability on the RREQ and secondly a RREQ message forwarding scheme which is implemented on Ad-hoc On-Demand Distance Vector Routing (AODV) routing protocol, a Bayesian probability based the AODV extended version based on a modified version of Bayesian probability (AODV_EXT_BP) that reduces routing overheads, by calculating the probability with respect to the neighbour density as well as the posterior probability. The performance of the AODV_EXT_BP is compared to that of extended version of AODV (AODV_EXT), AODV, Destination Sequenced Distance Vector, dynamic source routing and Optimized Link State Routing protocols and the simulation results show that the AODV_EXT_BP protocol achieves better results in all sectors.

Comparative Performance Analysis of Wireless RSSI in Wireless Sensor Networks Motes in Tropical Mixed-crop Precision Farm

To provide reliable and adequate network coverage whilst minimizing the cost of wireless sensor network (WSN) deployments, detailed knowledge of wireless signal propagation within the specific environments is required. There are many WSN devices on the market that have been developed using proprietary systems and therefore have different performances, although implementing similar standards. This paper presents a comparative performance measurement and analysis of three types of WSN devices evaluated for application in a mixed-crop farm. The results show that the Xbee-PRO maintains very strong RSSI values in open field measurements that are sometime 15 dBm higher than those obtained from the IRIS and Microchip motes. Overall, two important factors that influence WSN node performances are antenna height and the type of antenna used. Whip omni-directional antenna has been shown to double the range of the WSN node compared to a patch antenna. Results also show that the log-distance propagation model is a more flexible model that can be used to model a variety of channels, although it lacks standard global parameter values.

Modeling and simulation of near-earth wireless sensor networks for agriculture based application using OMNeT++

In recent years, there have been a number of reported studies on the design of communication protocols using simulation platform. However, most of the reported works were evaluated using simple or idealistic wireless communication channel modeling. Experimental results have shown that the characterization and modeling of wireless communication channel is important to achieve a successful implementation of wireless sensor network (WSN) systems in agricultural based application. This paper investigates the impact of propagation model towards WSNs system under OMNeT++ simulation environment. Several realistic propagation models for WSNs are also reviewed. Several well known empirical vegetation models, namely MED Weissberger Model and ITU-Recommendation model are implemented in OMNeT++ simulation platform. It is observed that propagation model used gives significant impact towards the network performances. The results show that a combination of plain earth (PE) and vegetation model give more realistic result and can best describe the behavior of actual WSN systems when deployed in a real environment. Antenna heights and vegetation density are important parameters that affect communication network coverage and connectivity.

Spatial and temporal variation of wideband indoor channels

Extensive studies of the impact of temporal variations induced by people on the characteristics of indoor wideband channels are reported. Singular Value Decomposition Prony algorithm has been used to compute the impulse response from measured channel transfer functions. The high multipath resolution of the algorithm has allowed a detailed assessment of the shapes of individual multipath clusters and their variation in time and space in indoor channels. Large- and small-scale analyses show that there is a significant dependency of the channel response on room size. The presence of people in the channel has been found to induce both signal enhancements and fading with short-term dynamic variations of up to 30 dB, depending on the number of people and their positions within the room. A joint amplitude and time of arrival model has been used to successfully model measured impulse response clusters.