Timely Random Access: Packet-based or Connection-based?

This paper studies random access protocols for timely status update systems with information freshness requirements, measured in terms of age of information (AoI). Considering an extensive network, a fundamental problem is how to schedule massive transmitters to access the wireless channel to achieve low network-wide AoI. 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 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. From the information freshness perspective, there should be conditions favoring either side. 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 whether packet-based or connection-based protocols should be used depends mainly on the payload size of data packets. Except for the case where the payload size of an update packet is very tiny, RTA outperforms FSA in average AoI because the established connections help avoid direct collisions of data packets.