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.