We consider a wireless broadcast network with a base station sending
time-sensitive information to a number of clients through unreliable channels.
The Age of Information (AoI), namely the amount of time that elapsed since the
most recently delivered packet was generated, captures the freshness of the
information. We formulate a discrete-time decision problem to find a
transmission scheduling policy that minimizes the expected weighted sum AoI of
the clients in the network.
We first show that in symmetric networks a Greedy policy, which transmits the
packet with highest current age, is optimal. For general networks, we develop
three low-complexity scheduling policies: a randomized policy, a Max-Weight
policy and a Whittle's Index policy, and derive performance guarantees as a
function of the network configuration. To the best of our knowledge, this is
the first work to derive performance guarantees for scheduling policies that
attempt to minimize AoI in wireless networks with unreliable channels.
Numerical results show that both Max-Weight and Whittle's Index policies
outperform the other scheduling policies in every configuration simulated, and
achieve near optimal performance
