Status Updates Over Unreliable Multiaccess Channels

TL;DR

This paper analyzes the timeliness of status updates over unreliable multiaccess wireless channels, comparing scheduled and ALOHA-like random access methods, and derives conditions to optimize the age of information.

Contribution

It provides a detailed analysis of AoI for scheduled and ALOHA-like access, offering new insights into their performance and optimization in unreliable multiaccess channels.

Findings

Scheduled access achieves lower AoI than ALOHA-like by a factor of about 2e.

Derived conditions for optimizing AoI in different access schemes.

Analyzed symmetric updating scenarios for equal AoI across nodes.

Abstract

Applications like environmental sensing, and health and activity sensing, are supported by networks of devices (nodes) that send periodic packet transmissions over the wireless channel to a sink node. We look at simple abstractions that capture the following commonalities of such networks (a) the nodes send periodically sensed information that is temporal and must be delivered in a timely manner, (b) they share a multiple access channel and (c) channels between the nodes and the sink are unreliable (packets may be received in error) and differ in quality. We consider scheduled access and slotted ALOHA-like random access. Under scheduled access, nodes take turns and get feedback on whether a transmitted packet was received successfully by the sink. During its turn, a node may transmit more than once to counter channel uncertainty. For slotted ALOHA-like access, each node attempts transmission in every slot with a certain probability. For these access mechanisms we derive the age of information (AoI), which is a timeliness metric, and arrive at conditions that optimize AoI at the sink. We also analyze the case of symmetric updating, in which updates from different nodes must have the same AoI. We show that ALOHA-like access, while simple, leads to AoI that is worse by a factor of about 2e, in comparison to scheduled access.