This paper investigates low-power random access protocols for timely status
update systems with age of information (AoI) requirements. AoI characterizes
information freshness, formally defined as the time elapsed since the
generation of the last successfully received update. Considering an extensive
network, a fundamental problem is how to schedule massive transmitters to
access the wireless channel to achieve low network-wide AoI and high energy
efficiency. In conventional packet-based random access protocols, transmitters
contend for the channel by sending the whole data packet. When the packet
duration is long, the time and transmit power wasted due to packet collisions
is considerable. In contrast, connection-based random access protocols first
establish connections with the receiver before the data packet is transmitted.
Intuitively, from an information freshness perspective, there should be
conditions favoring either side. This paper presents a comparative study of the
average AoI of packet-based and connection-based random access protocols, given
an average transmit power budget. Specifically, we consider slotted Aloha (SA)
and frame slotted Aloha (FSA) as representatives of packet-based random access
and design a request-then-access (RTA) protocol to study the AoI of
connection-based random access. We derive closed-form average AoI and average
transmit power consumption formulas for different protocols. Our analyses
indicate that the use of 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 reduces AoI significantly, especially when the
payload size is large. Overall, our investigation provides insights into the
practical design of random access protocols for low-power timely status update
systems