  In this paper, we study peak age of information (PAoI) performance of a novel
IoT solution for remote health-monitoring of first responders over TErrestrial
Trunked RAdio (TETRA) links. The solution features a set of sensors embedded in
a smart garment that periodically record and send physiological parameters of
first responders to a remote agent. The received data is analyzed by the remote
agent, which feeds back notifications and warnings to the first responders in
the form of electrotactile stimuli. The communication in the system is
performed over the TETRA Short Data Service (SDS), which is the default option
for the development of third-party applications and which has rather limited
capabilities. The choice of the PAoI as the parameter of interest is motivated
by its suitable to measure data freshness in IoT applications with periodic
monitoring. We derive closed-form expressions of PAoI for different
packet-management schemes allowed by the TETRA standard, and verify the
analytical results through extensive simulations under varying message
generation rates. Our results provide important insights on the expected PAoI
performance, which can be used for the system design guidelines. To the best of
our knowledge, this is the first work that analyzes AoI performance of TETRA
networks.
