144,114 research outputs found
Status Updates Over Unreliable Multiaccess Channels
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
Age of Information in Multicast Networks with Multiple Update Streams
We consider the age of information in a multicast network where there is a
single source node that sends time-sensitive updates to receiver nodes.
Each status update is one of two kinds: type I or type II. To study the age of
information experienced by the receiver nodes for both types of updates, we
consider two cases: update streams are generated by the source node at-will and
update streams arrive exogenously to the source node. We show that using an
earliest and transmission scheme for type I and type II updates,
respectively, the age of information of both update streams at the receiver
nodes can be made a constant independent of . In particular, the source node
transmits each type I update packet to the earliest and each type II
update packet to the earliest of receiver nodes. We determine the
optimum and stopping thresholds for arbitrary shifted exponential
link delays to individually and jointly minimize the average age of both update
streams and characterize the pareto optimal curve for the two ages
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