On Real-Time Status Updates over Symbol Erasure Channels

As sensing, control, and actuation become further integrated into modern communication infrastructures, special consideration must be given to the type of traffic generated by associated devices. Real-time decision making relies on the availability of accurate data and, as such, delivering status updates in a timely fashion is of paramount importance. The topics of real-time status updates and low- delay communications have received much attention in recent years. Within this context, this article presents new results by looking at the interplay between average timeliness and design decisions made at the physical layer for unreliable communication channels. This study focuses on the natural tension between the protection afforded by additional redundancy and the decoding delay associated with longer codewords. The average timeliness is adopted as a performance criterion, and a framework to efficiently compute the performance of various transmission schemes for the binary erasure channel is developed. The problem formulation precludes the use of asymptotically long codewords typical of information theory. Yet, the presence of limited feedback does not seem to boost performance in the present context. Rather, having accurate channel estimates is key in minimizing average timeliness. Numerical examples are included in this article to further illustrate the applicability of the findings.