Deterministic Patterns for Multiple Access with Latency and Reliability Guarantees

TL;DR

This paper compares deterministic and random access patterns for multiple devices aiming for reliable, low-latency communication, demonstrating that deterministic patterns can outperform random ones and simplify system design.

Contribution

It introduces a novel deterministic access pattern based on Steiner Systems for grant-free multiple access, analyzing its performance under different receiver models and demonstrating its advantages.

Findings

Deterministic patterns outperform random in reliability.

Deterministic access simplifies system design.

Approximate bounds closely match simulation results.

Abstract

We study a scenario in which multiple uncoordinated devices aim to achieve reliable transmissions within a given time frame. The devices are intermittently active and access a shared pool of channel resources in a grant-free manner by utilizing multiple transmissions (K-repetition coding). This allows them to achieve diversity and improve the reliability within a certain latency constraint. We focus on two access methods: one where devices choose K slots at random and another one where the access patterns are deterministic and follow a specific code design, namely the Steiner System. We analyze the problem under two signal models that involve different complexity for the receiver. First, collision model is considered, where only interference-free transmissions can be used and combined. Second, a model treating interference as noise is analyzed, where the receiver is capable of utilizing all K replicas, applying maximum ratio combining (MRC). For both signal models, we investigate receivers with and without successive interference cancellation (SIC). We develop approximations and bounds for the outage probabilities that very closely match simulation results. Overall, we show that deterministic access patterns have the potential to significantly outperform random selection in terms of reliability. Furthermore, deterministic access patterns offer a simplified system design.