07-05-2012, 04:38 PM
Sensor Network Motes
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Introduction
This dissertation describes our efforts to improve sensor network performance evaluation and
portability, within the context of the sensor network project Hogthrob. In Hogthrob, we faced
the challenge of building a sensor network architecture for sow monitoring. This application
has hard requirements on price and performance, and shows great potential for using sensor
networks. Throughout the project we let the application requirements guide our design choices,
leading us to push the technologies further to meet the specific goal of the application.
In this dissertation, we attack two key areas related to the design of this solution. We found
the current state of the art within performance evaluation to be inadequate and that the moving
to the next generation platforms is being held back by practical issues in porting existing software.
We have taken a pragmatic, experimental approach to investigate these challenges and
apart from developing the methodologies, we also present the results of our experiments.
In particular, we present a new vector based methodology for performance evaluation of
sensor network devices (motes) and applications. The methodology uses a benchmarking approach
to create an objective description of a mote, and further traces an application to extract
an abstract workload description from a running application. Combining these two are able to
speculative estimate the performance of an application across motes.
The Hogthrob Project
The work presented in this dissertation is part of Hogthrob research project. Named after the
captain of the Muppet Shows “Pigs in Space”, the Hogthrob project is a four year research
project (started in February 2004). The goal is to build a sensor network infrastructure for sow
monitoring. The project is a collaboration between three research institutions, and two industrial
partners.
The key idea in the project is the use of sensor network technology within the area of Sow
Monitoring. What can be observed and how? DIKU has focused on the sensor network infras-
Introductiontructure for this task. This dissertation is a continuation of my Masters Thesis and I will quote
the introduction of the Hogthrob project[64]:
SowMonitoring
Current sow monitoring equipment is based on RF-id ear tags and readers located at feeding
stations. This equipment has some advantages (its main goal is to control how much food sows
are eating) and a number of drawbacks:
• When looking for a given pig, the farmer has to place a hand-held reader close to an
animal—for large groups this can be time consuming. Legislation is underway that will
require farmers to let sows roamfreely in large pens. Thiswill expose this problemfurther.
• Correctly establishing the onset of estrus1 (heat period) is amajor issue for pig production.
The sows exhibit clear physical signs when the event occurs. Finding the exact moment
can be done purely by observation or augmented by using a detection system.
The available detection systems today rely on the fact that the sows are likely to approach
a bore more often (if one is available) during the heat period. Placing a bore in an adjacent
confinement and detecting the RF-id tags of the sows that approach it will provide a decent
indication. However, sows are housed in groups with a strict hierarchy. A sow low
in the hierarchy is unlikely to approach the bore. A purely RF-id based system will thus
not detect the beginning of a heat period for all pigs.
Implementing a sensor network by placing a sensor node on each sowprovides newinsights
and new solutions to the problems above.
Application Requirements
Monitoring sows in a large pen on a farm presents a concrete sensor network monitoring application
with many interesting challenges. The application requirements are imposed by the
farmers, not as a result of our imagination. The three major constraints are price, life time, and
form factor:
1. The profit margin of sow production is low and the equipment for each sow must be very
cheap in order to fit the budget (in the order of a few e).
2. The usability of the system on the farm will be drastically reduced if the nodes have to
be manually inspected too often. A lifetime of as much as “a few years” would be advantageous,
but in practice a lifetime of 6 months would be acceptable. The identification
systems used today are not maintenance free as the sows tend to loose or eat the tags.