  Age of information (AoI), a metric to analyse data freshness, is of interest
for time-critical applications in upcoming wireless networks. Besides, wireless
power transfer (WPT) is also essential to prolong lifetime of a wireless sensor
network. Thus, we study a flat-fading wireless powered cooperative network,
wherein a source and a relay charge their finite-sized capacitors by harvesting
energy from a remote power station. For two conventional decode-and-forward
(DF) and amplify-and-forward (AF) relaying, average AoI and peak AoI (PAoI) are
studied to show how the randomness of the data/power transfer channel and size
of the capacitors affect the age metrics, and when utilizing a cooperative
transmission is more beneficial than direct one. It is shown that, although the
power-limited relay imposes more delay overhead, the age metrics are improved
in some circumstances. Even for the DF scheme with more waiting time for signal
processing, we may achieve lower average PAoI due to enhancing the end-to-end
communications reliability. Furthermore, special cases of the proposed WPT
cooperative system is discussed, e.g. cases of full-power nodes and one-shot
successful data transmission. Finally, numerical results are provided to
highlight effects of transmission power, size of the capacitors, and path loss
exponent on the age metrics.
