Finite Blocklength Performance of Cooperative Multi-Terminal Wireless Industrial Networks

Cooperative diversity is one of the candidate solutions for enabling ultrareliable low-latency wireless communications (URLLC) for industrial applications. Even if only a moderate density of terminals is present, it allows in typical scenarios the realization of a high diversity degree. It is furthermore only based on a reorganization of the transmission streams, making it achievable even with relatively simple transceiver structures. On the downside, it relies crucially on the distribution of accurate channel state information while cooperative transmissions naturally consume time. With the current goal of providing latencies in the range of 1 ms and below, it is, thus, open if cooperative systems can scale in terms of the number of terminals and the overhead. In this paper, we study these issues with respect to a finite blocklength error model that accounts for decoding errors arising from “above-average” noise occurrences even when communicating below the Shannon capacity. We show analytically that the overall error performance of cooperative wireless systems is convex in the decoding error probability of finite blocklength error models. We then turn to numerical evaluations, where several design characteristics of low-latency systems are identified: First, the major performance improvement is associated with two-hop transmissions in comparison to direct transmissions. The additional improvement due to more hops is only marginal. Second, with an increasing system load, cooperative systems feature a higher diversity gain, which leads to a significant performance improvement despite the increased overhead and a fixed overall frame duration. Third, when considering a realistic propagation environment for industrial deployments, cooperative systems can be shown to generally achieve URLLC requirements.