Cyber Physical Security Solutions for Pervasive Health Monitoring Systems - E-Healthcare Systems and Wireless Communications - page 151

Cyber-Physical System
Characteristics

is usually made up of limited size medical
sensors for usability reasons, but the base
station managing the sensors is usually a
hand-held computer. A direct consequence
of this heterogeneity is potential bottleneck
in terms of computation, communication
and memory in the work-flow.
• Networking : CPS, unlike traditional stand-
alone embedded systems, usually require
their computational elements to have a
communication channel between each
other in order to provide its (usually co-
ordinated) services (Lee, Cyber Physical
Systems: Design Challenges, 2008). For
example, in an automobile CPS, sensors
monitoring the car cabin conditions com-
municate with the car radio in order to
compensate for external conditions such
as speed increases and window opening.
Further, with CPS, it is possible that every
physical aspect of a system is controlled
by a cyber element. Therefore, networking
capabilities are required at different scales
of the system.

From a design point of view, CPS platforms are
usually an amalgamation of electro-mechanical
sensors and actuators, a communication stack,
memory and a processing unit and deployed in
an environment where a physical process is op-
erating. CPS can be classified as centralized or
distributed based on how the cyber-elements are
deployed (Tang, 2008). An example of a central-
ized CPS is an implantable cardiac defibrillators
(ICDs) or pacemakers which embedded inside a
person's chest cavity (as a part of the cardiovas-
cular process) to observe its behavior (cardiac
cycle) and correct it, in the event of an abnormal
behavior (arrhythmia). Example of a distributed
CPS is an automobile control system where sen-
sors from the engine provide temperature data
to a microprocessor dedicated to manage engine
functionality, which then communicates the
data through an in-car network to a controller in
dashboard which displays this information to the
driver. Irrespective of the type, a CPS has three
principal characteristics:

Cyber-Physical System Work-Flow

• Environment Coupling : CPSs have cyber
and physical elements in a very tightly cou-
pling. Any change in the behavior of the
physical process results in a change in the
cyber element and vice-versa. Prominent
examples include medical devices such as
ICDs. Modeling physical processes (from
a control theoretic or formal methods per-
spective, for example) becomes an impor-
tant part of designing and testing CPS.
• Heterogeneity : CPSs are usually made up
of heterogeneous computational elements
with order of magnitude difference in ca-
pabilities. Sensors deeply embedded in
physical processes for monitoring purpos-
es have limited capabilities, while those
entities which manage them are much
more capable. For example, a PHM-CPS

We can categorize the work-flow of CPSs into
three main functions: (1) Monitoring : The most
fundamental aspect of CPS and deals with monitor-
ing the physical process within the CPS. It is also
used to provide feedback on any past actions taken
by the CPS and ensure correct operations in the
future; (2) Processing : This deals with analyzing
the data collected during monitoring to determine
whether the physical process is meeting certain
pre-defined criteria. In situations where the criteria
are not being satisfied, the corrective actions are
determined which when executed ensures the
criteria is satisfied. For example, a data-center
CPS can observe its thermal characteristics, de-
velop a model to predict the temperature rise with
respect to various scheduling algorithms, which
can be used to determine future job (Tang, 2008);