Ismo Hakala

From vertical to horizontal architecture: a cross-layer implementation in a sensor network node

Some of the main challenges related to wireless sensor networks implementation are low-quality communication, energy conservation, resource-constrained computation, distributed network management, data processing and the scalability of the protocols. This combination makes the implementation of software a demanding task and encourages to new approaches when thinking of software architecture.In this paper an architecture combining a low protocol stack with a cross-layer management entity is presented. One of the main ideas behind the architecture presented is to make application programming easier and to simplify the protocol stack in such a way that it would suit better for the limited resources available. The role of the cross-layer management entity is to offer a shared data structure and to take care of some sensor network specific functions, like topology management and power saving. It also provides certain services that applications and the layers in the protocol stack can use.This architecture has been created specially for needs of wireless sensor networks implementation and the special attention has been paid to modularity and testability of implementation. An implementation based on this cross-layer architecture, CiNet, is also presented in this paper. The functionality of the architecture and the CiNet network was verified by using two different protocol stacks. Wireless communication of the network is based on the 802.15.4 technology.

Wireless Sensor Network in Environmental Monitoring - Case Foxhouse

Environmental monitoring in agriculture is an interesting and promising area of application for wireless sensor networks. Wireless sensor networks can deliver valuable information about environment, animals and their habitat. This paper describes a case where such sensing application was implemented with biologists. The wireless sensor network collected data in hard outdoors conditions over a period of one year, during which luminosity, temperature and humidity were measured in a fox house. In addition to habitat monitoring, the reliability of the wireless technology used was also one of the subjects of the study. This paper describes the Foxhouse Case implementation, reports on its results and discusses the observations made during project.

Design of Low-Cost Noise Measurement Sensor Network: Sensor Function Design

In this paper, we report the sensor function design and implementation of a wireless sensor network application for measuring environmental acoustic noise. The system is built on ATmega128 and CC2420 platform. The protocol stack is based on CiNet stack with a global synchronization scheme and supports multi-hop communications. Strict filtering function specified by ITU-R 468 (namely A-weighting) is followed. Both the indoor and outdoor test results were compared with standard sound level meters (CESVA SC-20c and Pulsar94) and showed a less than ±2dB error in both short-term and longterm measurement. Power consumption has been measured that a single AA-type battery can sustain the application. Comparing to the traditional noise measurement method, our wireless sensor network solution is much lower in cost, able to offer real-time data with sensed data timely coherent, and requests least attention after deployment.

Effects of temperature and humidity on radio signal strength in outdoor wireless sensor networks

Many wireless sensor networks operating outdoors are exposed to changing weather conditions, which may cause severe degradation in system performance. Therefore, it is essential to explore the factors affecting radio link quality in order to mitigate their impact and to adapt to varying conditions. In this paper, we study the effects of temperature and humidity on radio signal strength in outdoor wireless sensor networks. Experimental measurements were performed using Atmel ZigBit 2.4GHz wireless modules, both in summer and wintertime. We employed all the radio channels specified by IEEE 802.15.4 for 2.4GHz ISM frequency band with two transmit power levels. The results show that changes in weather conditions affect received signal strength. Of the studied weather variables, variation in signal strength can be best explained by the variation in temperature. We also show that frequency diversity can reduce the effects of channel-specific variation, and the difference between the transmit power levels.

The effect of time and place dependence when utilizing video lectures

In many learning institutes, diversification of teaching with the help of various technologies has become an essential part of educational arrangements. With the increase in the use of networks for teaching purposes, the use of streaming videos is now one of the possibilities to be reckoned with in trying to increase flexibility in studies. Specially recorded on-demand videos provide the students with better chances to decide when, where and how to study. Information on how students use on-demand videos can be obtained, apart from student questionnaires, from the log files of a media server. These files offer an information source that, on the one hand, is diverse but, on the other, cumbersome and less used. This article examines, with the help of the log files of the media server, matters related to time and place dependence and the use of videos by the students. The investigation is based on the analysis of the log data entered about videos transmitted during the masters education programme in information technology in 2008.

A Transmission Scheduling for Data-Gathering Wireless Sensor Networks

In this paper we present a transmission scheduling protocol for data-gathering Wireless Sensor Networks (WSN). We focus on the delivery performance in term of overall Packet Receive Ratio (PRR) at the sink node. In order to reduce the energy consumption and increase the overall delivery performance, elaborated scheduling algorithm is applied to the transmission and relaying of data packets, based on a beacon-broadcasting global synchronization. We tested the protocol using CiNet nodes, which is built on IEEE 802.15.4 compliant radio modules CC2420 and Jennic JN5148, and obtained significant delivery improvement in multihop scenarios. This protocol is suitable for energy-hungry data gathering wireless sensor networks in which the sensor nodes use a short time window for radio activities in order to save energy.

H.264 QoS and application performance with different streaming protocols

Streaming techniques, including the selected streaming protocol, have an effect on the streaming quality. In this study, the performance of three different streaming protocols in a disturbed communication channel is evaluated with a modified version of the FFPlay player. A H.264 encoded video is used as a test sequence. The number of displayed image frames, the frame rate and playout duration are used as objective metrics for QoS. The metrics brings out differences of streaming protocols in our test environment. They are measured at the application level and have a connection to the user experience.

Wireless strain gauge network — Best-hall measurement case

Wireless sensor networks can be used to perform structural monitoring. Strain gauges, which can be glued on or integrated to the observed material, are the most common nondestructive sensing elements for measuring surface strain. Wireless strain gauge measurement system makes strain measurements more flexible while opening new targets of application in addition to those that traditional wired strain measuring systems can offer. We have implemented a long term strain measurement in a PVC-covered hall using wireless sensor network. In this paper we evaluate the functionality and suitability of the developed wireless system for this kind of monitoring. The paper discusses the experiences gained in the development and utilization of a wireless strain gauge measurement system. The calibration of measurement system as well as energy consumption issues are also brought under observation along with the reliability of communication aspects in the described measurement case.

Towards adaptive localization in wireless sensor networks

It is often useful or even indispensable to know the locations of the nodes in a wireless sensor network (WSN), from both network functionality and applications point of view. A potential yet one of the most challenging method is to utilize received signal strength indicator (RSSI) for distance estimation. Albeit easily adopted, using of RSSI is notorious for imprecise distance estimates which can lead to inaccuracies in location estimates. In this paper, we study RSSI-based localization in WSNs through simulation experiments. We evaluate and compare a hybrid algorithm and its modifications with well-known range-based and range-free localization algorithms. Simulation results indicate that hybrid algorithms which adapt to varying conditions are more appropriate for RSSI-based localization on a broad scale. We could further improve the location accuracy of the studied hybrid algorithm(s) by applying a variant proposed by us. More importantly, it was observed that even better results could be achieved if each node were able to choose the most suitable algorithm individually. This kind of local adaptivity in localization seems a promising approach in diverse and dynamical environments, which are, for RSSI-based localization in particular, extremely challenging.

Road traffic detection using wireless noise sensors

In this paper we present our experimental result of using wireless noise sensor network (WNSN) to detect road traffic. With the features implemented in our network such as multipoint measuring, synchronization, real-time data availability, and strict compliance of sound level meter (SLM) standard IEC 61672:2003, we assert the possibility of using WNSN to detect road traffic, such as vehicle amount, size, and velocity. This application can be extended and integrated as a part of Intelligent Transportation System (ITS).