Short Packet Structure for Ultra-Reliable Machine-type Communication: Tradeoff between Detection and Decoding

TL;DR

This paper investigates short packet structures for ultra-reliable low-latency machine-type communication, analyzing detection and decoding tradeoffs, and proposes a superimposed sequence approach that balances error probability and flexibility.

Contribution

It introduces a superimposed sequence structure for short packets in URLLC, deriving error probabilities and demonstrating tradeoffs between detection overhead and decoding performance.

Findings

Superimposed sequences can optimize detection and decoding tradeoffs.

Higher detection overhead improves PER but increases error probability.

Superimposed structure offers flexibility without multiple codebooks.

Abstract

Machine-type communication requires rethinking of the structure of short packets due to the coding limitations and the significant role of the control information. In ultra-reliable low-latency communication (URLLC), it is crucial to optimally use the limited degrees of freedom (DoFs) to send data and control information. We consider a URLLC model for short packet transmission with acknowledgement (ACK). We compare the detection/decoding performance of two short packet structures: (1) time-multiplexed detection sequence and data; and (2) structure in which both packet detection and data decoding use all DoFs. Specifically, as an instance of the second structure we use superimposed sequences for detection and data. We derive the probabilities of false alarm and misdetection for an AWGN channel and numerically minimize the packet error probability (PER), showing that for delay-constrained data and ACK exchange, there is a tradeoff between the resources spent for detection and decoding. We show that the optimal PER for the superimposed structure is achieved for higher detection overhead. For this reason, the PER is also higher than in the preamble case. However, the superimposed structure is advantageous due to its flexibility to achieve optimal operation without the need to use multiple codebooks.