Fundamental Tradeoffs in Uplink Grant-Free Multiple Access with Protected CSI

TL;DR

This paper explores the fundamental tradeoffs between reliability, latency, and accessibility in uplink grant-free multiple access for 5G URLLC, proposing a hierarchical coding scheme to protect channel state information against pilot-aware attacks.

Contribution

It introduces a novel hierarchical 2-D feature coding scheme to safeguard CSI, enabling a fundamental analysis of reliability, latency, and accessibility tradeoffs in grant-free uplink access.

Findings

Derived closed-form reliability expressions for large-scale SIMO systems.

Identified and characterized the reliability-latency and reliability-accessibility tradeoffs.

Demonstrated how CSI protection enhances URLLC performance.

Abstract

In the envisioned 5G, uplink grant-free multiple access will become the enabler of ultra-reliable low-latency communications (URLLC) services. By removing the forward scheduling request (SR) and backward scheduling grant (SG), pilot-based channel estimation and data transmission are launched in one-shot communications with the aim of maintaining the reliability of $99.999\% $ or more and latency of 1ms or less under 5G new radio (NR) numerologies. The problem is that channel estimation can easily suffer from pilot aware attack which significantly reduces the system reliability. To solve this, we proposed to apply the hierarchical 2-D feature coding (H2DF) coding on time-frequency-code domain to safeguard channel state information (CSI), which informs a fundamental rethinking of reliability, latency and accessibility. Considering uplink large-scale single-input multiple-output (SIMO) reception of short packets, we characterize the analytical closed-form expression of reliability and define the accessibility of system. We find two fundamental tradeoffs: reliability-latency and reliability-accessibility. With the the help of the two fundamental trade-offs, we demonstrate how CSI protection could be integrated into uplink grant-free multiple access to strengthen URLLC services comprehensively.