Variable Length Differential Encoding for Real-Time Status Updates

Timely reception of information is of utmost importance in many cyber-physical systems. We study timely status update schemes for a single source. We consider a scheme which exploits the temporal correlation in source messages to send differential information to the receiver, over an unreliable channel. In this scheme, the source sends the true state information, interleaved with differential messages. We observe that the differential encoding improves the timeliness performance even in the absence of feedback, if the codeword lengths for both differential and true messages are chosen judiciously.