On Delay-Constrained Transmissions of a Finite Number of Short-Length Packets

In industrial Internet-of-Things (IoT) applications including smart factories, railway/aircraft operating and control systems, and so on, it is expected to deliver a bundle of packets with a delay constraint. In this paper, we study delay-constrained transmissions where a user or device is to send a bundle of short-length packets within a certain time limit through radio resource blocks shared with others. We first derive a closed-form expression for (a tight upper-bound on) the probability of decoding error when a short-length packet is transmitted through multiple channels (for a high diversity gain under fading). Using the expression, we then study the performance in terms of delivery delay for a bundle of packets using the notion of queuing systems. It is shown that the derived expressions agree with simulation results, which demonstrates that those can be used to design delay-constrained transmission systems to support industrial IoT applications where a bundle of packets has to be delivered within a certain short time limit with high reliability.