Delays, Clocks, Timing and Reliability in Networked Control Systems: Theories, Protocols and Implementations

Abstract

Wireless networks are increasingly used in networked control systems. An important challenge is to provide delay guarantees for every packet in the system. In this work, we propose a framework for real-time wireless networks. The core of this framework is an analytical model that jointly considers several practical concerns that include the strict delay bound for each packet, the throughput requirement of each client, and the unreliable nature of wireless transmissions.

Based on the model, we discuss two important functions for real-time wireless networks. One is admission control, which consists of determining whether it is feasible to fulfill the demands of all clients in the system. The other is finding a feasibility optimal scheduling policy that fulfills all feasible systems. For the former, we establish a necessary and sufficient condition for feasibility. For the latter, we propose a simple online scheduling policy that turns out to be feasibility optimal.

We then discuss the problem of broadcasting real-time flows over wireless links. The most important difference between broadcast and unicast is that, due to the lack of ACKs, there are no per- transmission feedbacks in wireless broadcast. For this problem, we establish a framework for designing scheduling policies. We then propose a scheduling policy that is feasibility optimal when network coding is not employed. We also develop tractable scheduling policies for two different kinds of coding schemes, namely, XOR coding and linear coding.

Award ID: 1232602