  In this paper, we consider a system where multiple low-power sensors
communicate timely information about a random process to a sink. The sensors
share orthogonal subchannels to transmit such information in the form of status
update packets. Freshness of the sensors' information at the sink is
characterized by the Age of Information (AoI), and the sensors can control the
sampling policy by deciding whether to take a sample or not. We formulate an
optimization problem to minimize the time average total transmit power of
sensors by jointly optimizing the sampling action of each sensor, the transmit
power allocation, and the subchannel assignment under the constraints on the
maximum time average AoI and maximum power of each sensor. To solve the
optimization problem, we use the Lyapunov drift-plus-penalty method. Numerical
results show the performance of the proposed algorithm versus the different
parameters of the system.
