Stabilizing a linear system using phone calls when time is information
This work addresses the challenge of event-triggering control with zero-payload rate for systems like phone call networks, generalizing previous strategies and revealing fundamental limits in using timing information for stabilization.
The paper tackles the problem of stabilizing a scalar linear system over a timing channel, where information is encoded in transmission timestamps and subject to random delays, showing that stabilization requires the timing capacity to be at least as large as the system's entropy rate, and provides an almost tight sufficient condition for exponentially distributed delays.
We consider the problem of stabilizing an undisturbed, scalar, linear system over a "timing" channel, namely a channel where information is communicated through the timestamps of the transmitted symbols. Each symbol transmitted from a sensor to a controller in a closed-loop system is received subject to some to random delay. The sensor can encode messages in the waiting times between successive transmissions and the controller must decode them from the inter-reception times of successive symbols. This set-up is analogous to a telephone system where a transmitter signals a phone call to a receiver through a "ring" and, after the random delay required to establish the connection; the receiver is aware of the "ring" being received. Since there is no data payload exchange between the sensor and the controller, this set-up provides an abstraction for performing event-triggering control with zero-payload rate. We show the following requirement for stabilization: for the state of the system to converge to zero in probability, the timing capacity of the channel should be, essentially, at least as large as the entropy rate of the system. Conversely, in the case the symbol delays are exponentially distributed, we show an "almost" tight sufficient condition using a coding strategy that refines the estimate of the decoded message every time a new symbol is received. Our results generalize previous zero-payload event-triggering control strategies, revealing a fundamental limit in using timing information for stabilization, independent of any transmission strategy.