Man Wah Chiang1, Zeljko Zilic1, Katarzyna Radecka2 and Jean-Samuel Chenard1
1Microelectronics and Computer Systems Laboratory, 2Department of ECE,
McGill University Concordia University
{manwah,zeljko,jsamch}@macs.ece.mcgill.ca kasiar@ece.concordia.ca
Abstract
Wireless sensor networks (WSNs) are being
increasingly used in applications where low energy
consumption and low cost are the overriding
considerations. With increased use, their reliability,
availability and serviceability need to be addressed from
the outset. Conventional schemes of adding redundant
nodes and incorporating reliability in control protocols
can effectively improve only the reliability of the overall
WSN. The availability and serviceability of WSN nodes
can be addressed by providing the remote testing and
repair infrastructure for the individual sensor nodes that
is well matched with existing on-board test infrastructure,
including standard JTAG chains. In this paper, we
propose and evaluate scalable architectures of WSN
nodes for increased availability as well as implement the
proposed solutions using COTS components.
1 Introduction
As Wireless Sensor Networks (WSNs) are expected to
be adopted in many industrial, health care and military
applications, their reliability, availability and
serviceability (RAS) are becoming critical. In traditional
networking systems, providing sufficient RAS can often
be absorbed in the network cost. Nevertheless, as noticed
early [1], network designers face "two fundamentally
conflicting goals: to minimize the total cost of the network
and to provide redundancy as a protection against major
service interruptions."
Physical redundancy is the common technique used to
ensure the reliability of a system. By placing multiple
independent nodes, the network is protected from singlepoint
failures in hardware or software. For availability and
serviceability, remote testing and diagnostics is needed to
pinpoint and repair (or bypass) the failed components that
might be physically unreachable.
Severe limitations in the cost and the transmitted energy
within WSNs negatively impact the reliability of the nodes
and the integrity of transmitted data. Traditionally, welldefined
transport layer communication protocols are being
used to ensure the end-to-end data transmission integrity.
However, most often WSNs sacrifice from outset the data
integrity by eliminating the reliable transport layer. Most
of the early wireless sensor networks were used mainly for
the environmental data collection of relatively non-critical
data, such as the temperature of the environment. Missing
a small portion of data or corrupting measurement results
does not present a problem over the sufficiently long
measurement period. However, remote testing and repair
are extremely difficult when the data transmission integrity
is not guaranteed. As a result, reliability, availability and
serviceability of WSNs are severely affected by these
constraints.
In this paper, we examine WSN nodes and propose the
necessary infrastructure required for increasing both the
availability and serviceability of the system, in spite of the
absence of a reliable transport layer. Further, we
incorporate the proposed approach within the layered
approach to system test [2], which is becoming a necessity
for achieving transparent test application in systems where
different communication protocols might coexist at all
layers. By this approach, the test semantics is incorporated
in a sufficiently high protocol layer, e.g., application layer,
such that all the layers below remain unchanged and the
full functionality of lower layers is applied for testing. For
example, data encryption might be needed in some test
and configuration downloads, and the layered approach
allows the test application to reuse existing encryption
protocols at lower layers.
The paper is organized as follows. In Section 2, we
present the background on wireless sensor networks and
relevant system reliability metrics. Layered approach to
WSN design is presented as well. The general
requirements for the proposed infrastructure are also
outlined. Test and availability requirements of WSNs are
elaborated in Section 3. Approaches to designing the Test
Interface Modules are presented in Section 4. In Section 5,
a case study of a WSN node based on the Texas
Instrument MSP430 microcontroller family is examined.
Experimental results are also presented for a case of WSN
nodes built on an in-house developed research and
teaching platform McGumps.
2 Background
2.1 Wireless Sensor Networks
A wireless sensor network is made up of three
components: Sensors Nodes, Task Manager Node (User)
and Interconnect Backbone, as shown in Figure 1.
Each Sensor Node can contain various sensors and
actuators that are used to collect the data and control
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Paper 43.2
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