  We propose a variant of the Age of Information (AoI) metric called
Channel-Aware Age of Information (CA-AoI). Unlike AoI, CA-AoI takes into
account the channel conditions between the source and the intended destination
to compute the "age" of the recent most update received by the destination.
This new metric ensures that the resource allocation is not heavily tilted
towards the sources with poor channel conditions. We design scheduling policies
for multi-sensor systems in which sensors report their measurements to a
central monitoring station via a shared unreliable communication channel with
the goal of minimizing the time-average of the weighted sum of CA-AoIs. We
initially derive universal lower bounds for the freshness objective. We show
that the scheduling problem is indexable and derive low complexity Whittle
index based scheduling policies. We also design stationary randomized
scheduling algorithms and give optimization procedures to find the optimal
parameters of the policy. Via simulations, we show that our proposed policies
surpass the greedy policy in several settings. Moreover the Whittle Index based
scheduling policies outperform other policies in all the settings considered.
