Fixed Length Differential Encoding for Real-Time Status Updates

Abstract

We consider the 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 paper, we study periodic data transmission schemes at a single source which 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. For a fixed length coding, we show that the differential encoding improves the timeliness performance only if the receiver's feedback is available.