20-12-2012, 05:02 PM
CONTEXT MONITORING OF A PATIENT USING WIRELESS NETWORKS
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Abstract: -
The paper describes a network that has been intended for context sensing, especially for
activity monitoring of a patient. It consists of multiple sensors such as heart monitoring,
temperature, magnetic field sensors etc. that are attached to the human body. To access the
sensor information and to make flexible sensor configurations feasible, an appropriate sensor
based Body Area Network (BAN) will be presented. A combination of wireless and wired
technologies is best suited for the specific application, in terms of robustness, energy consumption,
privacy and integrability into everyday outfits or some wearable platforms. After introducing the
network architecture, the paper describes the platform developed for wearable context monitoring
system.
The communication channels within such a Body Area Network (BAN) network can be
either completely wire-based, wireless or a mixture of both. The network may have static or
dynamic, single-path or multi-path routing algorithms with a flat or a hierarchical topology.
Introduction: -
Context sensing or context awareness is said to be one of the most important properties of
future computer systems. Context awareness can be described as the ability of a system to model
and recognize what the user is doing and what is going on around him and to use this information
to automatically adjust its configuration and functionality.
One aspect that needs to be addressed in order to realize this vision is how context
information can be obtained. It is obvious, that a single physical sensor alone can not provide
enough information to characterize the user’s situation. Therefore, the use of multiple
heterogeneous sensors, distributed over the user’s body. These simple sensors provide relevant
information on the user’s situation. The challenges arising from this approach are manifold
a) The management of multiple, distributed sensors in a common framework.
b) To interconnect the sensors, an adequate Body Area Network BAN) is required.
IMPLEMENTATION
This section focuses on the wireless part of the network and gives a short overview of our
hardware platform used for wearable context monitoring and the corresponding wireless protocols.
Hardware Nodes
Overview:
The requirements for the hardware of the central master and it’s slaves are: low-power
operation, low hardware complexity and minimum software overhead but at the same time
being flexible for different applications and different combinations of sensors. The modules
should be small to allow realistic context monitoring. Considering the application of the nodes,
a transmission range of approximately one meter is sufficient. Higher transmission ranges
require higher transmission powers thus increasing power consumption, which should be
avoided. Fig. a shows the schematics of such a node.
Transceiver:
Many transceivers and transceiver modules from different companies1 are available in the
market. The DR3001 from RF Monolithics (RFM) is widely used in this context The DR3001 is
one of the smallest off-theshelf modules (1.8 x 1.8cm2) and operates in the SRD-Band (Short
Range Devices Band) at 868.35MHz. It needs almost no additional components, is designed
for short-range communication and allows adjusting the radiated power (up to 1.2mW). The
transceiver module is connected to a __4 short PCB stub antenna. A spiral-antenna would
allow even smaller PCB designs.
Communication Protocols:
The requirements for our wireless communication protocols were simplicity, flexibility,
minimum overhead and automatic detection and integration of new sub networks. Two protocol
variants were implemented and compared. Both variants allow transmission of data packets with
different lengths and can handle both burst and continuous transmission.
1) Description of Protocol A and B:
Protocol A uses polling to address the slaves of the network. It consists of an initializing
phase to scan the network for available slaves and a data transmission phase in which the
master polls all the slaves that responded in the initializing phase.
Conclusion:
We have presented a network for interconnecting multiple, distributed bodyworn sensors
for context sensing. The use of wired and wireless communication channels as well as the
hierarchical network architecture has been discussed and motivated by the requirements of our
specific application: integration of the sensors into the user’s outfit, low power consumption, low
interference with other systems, privacy, and efficient usage of hardware resources. Apart from the
network architecture, an implementation of an experimental hardware platform has been
presented. Future work will focus on miniaturization of the network nodes and optimization of the
protocols.