  This paper studies low-power random access protocols for timely status update
systems with information freshness requirements, measured by age of information
(AoI). In an extensive network, a fundamental challenge is scheduling a large
number of transmitters to access the wireless channel in a way that achieves
low network-wide AoI while consuming minimal power. Conventional packet-based
random access protocols involve transmitters contending for the channel by
sending their entire data packets. When the packet duration is long, the time
wasted due to packet collisions can be significant. In contrast,
connection-based random access protocols establish connections with the
receiver before transmitting data packets. From an information freshness
perspective, there should be conditions that favor one approach over the other.
We present a comparative study of the average AoI of packet-based and
connection-based random access protocols. Specifically, we consider frame
slotted Aloha (FSA) as a representative of packet-based random access and
design a request-then-access (RTA) protocol for connection-based random access.
Our analyses indicate that the choice between packet-based or connection-based
protocols depends mainly on the payload size of update packets and the transmit
power budget. In particular, RTA saves power and significantly reduces AoI,
especially when the payload size is large. Overall, our investigation offers
insights into the practical design of random access protocols for low-power
timely status update systems.
