Differential Encoding for Real-Time Status Updates
Abstract
We consider the problem of status updates of a physical process over an unreliable channel. In
this setting, one may not be able to reliably transmit the current state at all times. Instead, one
is interested in the timeliness of the accurately received information. This is a setting for several
cyber-physical system applications that require real-time monitoring and control. In this thesis,
fi rst we have studied the periodic data transmission schemes for highly correlated source, that
can always exploit the temporal correlation in the source messages. When the source has no
feedback, it can periodically send the actual information, interspersed with differential messages.
On the availability of receiver's feedback at the source, it can decide to send either the differential
or the actual information, at each transmission opportunity. We show a stochastic ordering
among the update schemes, to conclude that the differential encoding improves the timeliness
performance, only if the receiver's feedback is available. We also identify the scenarios when
it is advantageous to use differential encoding with feedback, considering a cost for feedback
messages. Second, we have studied the data transmission scheme for general correlated sources
that can elect to transmit actual or differential state information depending on the current
state. This encoding scheme generalizes the actual and differential updates schemes. Using this
generalized scheme, we quantify the timeliness gains for general Markov sources using block
Markov chains.