In networked control, there is locational freedom in choosing the node at which to locate the controller, so as to mitigate the effects of packet losses in the network. What is the optimal location for the placement of the control logic? Second, what is the optimal control law in that position? The difficulty in answering these two questions is that analysis of optimality in networked control systems subject to random packet drops suffers from Witsenhausen's 'non-classical information pattern'. Thus, the general problem is considered intractable. We make headway on this problem by using a "Long Packet Assumption", LPA, which allows packets to be arbitrarily long. This is not intended for implementation, but only to develop a lower bound on the cost. In particular, under this assumption the optimal controller location can be shown to be collocated with the actuator. For this position, under the LPA, we can also calculate the optimal cost, which is then a lower bound on the optimal cost for the original problem for all locations. Despite the apparent strength of the LPA, we have found that this lower bound is often close to currently realizable upper bounds. This establishes the near optimality of currently implementable controllers in such instances. Using the lower bound on cost we obtain a necessary condition for stabilizability over all controller locations. This condition matches known sufficient conditions for some special cases, thus establishing a necessary and sufficient condition for location optimized stabilizability of networked control systems with packet loss.

Cyber-physical systems are networked, component-based, real-time systems that control and monitor the physical world. We need software architectures that limit fault-propagation across unreliable components. This paper introduces our simplex reference model which is distinguished by: a plant being controlled in an external context, a machine performing the control, a domain model that estimates the plant state, and the safety requirements that must be met. The simplex reference model assists with constructing CPS architectures which limit fault-propagation. We present a representative case study to highlight the ideas behind the model and our particular decomposition.

Patterns are a valuable method for communicating software engineering expertise about proven solutions for common problems. This paper evaluates the use of domain-independent patterns in a case study of Etherware, a middleware for networked control with a real-time, safety-critical applications model. The case study illustrates the positive and negative impact that four existing patterns have on availability, reliability, and robustness for real-time, safety-critical systems. In particular, we observe Etherware's specialized usage of the filter pattern, confirm this usage among other middleware technologies, and subsequently present the adaptive control filter, a design pattern for real-time, safety-critical middleware which can mitigate timing dependencies in networked control

This paper investigates the behavior of a group of autonomous robots evolving in a polygonal environment according to a "move away from the closest neighbor" heuristic. We demonstrate that this distributed coordination algorithm optimizes an aggregate cost function that measures how uniformly distributed are the robots in their environment. Our technical approach based on non-smooth analysis and computational geometry unveils a sphere-packing problem. The algorithm is implemented in a testbed of indoor mobile robots equipped with sonar. We develop novel approaches for improving single point sonar scan performance. These algorithms are then shown to have improved reliability, resolution and speed in distributed environments as compared to other scanning methods.