CSCI 5854: Lecture 1 - What is CPS?

This course is about the modeling, design and analysis of Cyber-Physical Systems (CPS). What are CPS?

As the name suggests, CPS integrate computational elements inside a physical environment wherein the different physical and computational subsystems interact with each other. In other words, these are like the traditional embedded systems. However, in that sense any computation that is worth considering ``integrates computational elements inside a physical environment''. Ergo, every computer system becomes a CPS. However, CPS form feedback loops so that the physical system's behavior is affected by the computation and vice-versa To specialize our attention to particular class of systems, let us write down a few characteristics of CPS and provide examples of systems we will include in our study, as well as exclude certain classes of systems.

As you will realize, deciding what to include/exclude inside the aegis of "CPS" can be tricky. However, rather than provide a criteria to exclude, we will focus on a criterion of inclusion.

What is a CPS?

Let us consider an examples of CPS in the description below.

Example-1: Adaptive Cruise Control Systems

An adaptive cruise controller is increasingly a feature in many modern automobile. It uses radar, lidar and vision sensors to sense the presence of vehicles in front of the driver. It then controls the speed of the car to maintain a constant distance between the vehicle in front by application of throttle or brakes. The system interacts with the driver, allowing the driver to set a desired speed and following distance, and warns the user of impending collisions. It also interacts with other systems inside the car such as the anti-lock braking system.

Block diagram of an imagined adaptive cruise control.

Block diagram of an imagined adaptive cruise control.

Here are some of the notable aspects of this system:

Note that I am deliberatively drawing somewhat tedious distinction between the main feedback loop of the system and the interactions with other systems.

Example-2: Artificial Pancreas

People with type-1 diabetes will need to control their blood glucose levels by the external administration of insulin. Insulin is a hormone that causes a reduction in the blood glucose levels of the patient. An artificial pancreas device controls how much insulin the patient gets in order to keep the blood glucose levels within a normal range of around 70-180 mg/dl.

Block diagram of a closed loop artificial pancreas system.

Block diagram of a closed loop artificial pancreas system.

The application is very similar to a cruise control or a thermostat. If blood glucose level is high, provide more insulin and withhold the insulin if low. However, the system is complicated in many ways. Insulin once given into the body sticks around for up to 4 hours and cannot be withdrawn easily. In other words, imagine a car with a sticky accelerator pedal but no brakes. Once again, we observe some characteristics:

Here are some of the notable aspects of this system:

Other Examples

Thus far, we have highlighted the key aspects of a CPS: real-time embedded software, feedback, running in a safety critical setting with a highly uncertain environment. Finally, humans and other systems are present in this environment and interact with the CPS under study.

Numerous other situations also have these characteristics:

Foundations for Cyber-Physical Systems

The aim of this course is to provide foundations for CPS. What form do these foundations take? What is the use of such foundations?

The Term Cyber-Physical Systems

Who came up with the term Cyber-Physical Systems? For the longest time, these systems were variously called real-time embedded systems or hybrid dynamical systems, depending on your perspective.

The term Cyber-Physical Systems was coined by Dr. Helen Gill of the US National Science Foundation (NSF) in 2006 (see here). Note however, that the closely related study of cybernetics goes back to the work of Norbert Wiener during the 1940s and 50s. Here is how Kolmogorov defines Cybernetics

".. a science concerned with the study of systems of any nature which are capable of receiving, storing, and processing information so as to use it for control .. " (see here)