  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.
