  This paper investigates a wireless-powered Internet of Things (IoT) network
comprising a hybrid access point (HAP) and two devices. The HAP facilitates
downlink wireless energy transfer (WET) for device charging and uplink wireless
information transfer (WIT) to collect status updates from the devices. To keep
the information fresh, concurrent WET and WIT are allowed, and orthogonal
multiple access (OMA) and non-orthogonal multiple access (NOMA) are adaptively
scheduled for WIT. Consequently, we formulate an expected weighted sum age of
information (EWSAoI) minimization problem to adaptively schedule the
transmission scheme, choosing from WET, OMA, NOMA, and WET+OMA, and to allocate
transmit power. To address this, we reformulate the problem as a Markov
decision process (MDP) and develop an optimal policy based on instantaneous AoI
and remaining battery power to determine scheme selection and transmit power
allocation. Extensive results demonstrate the effectiveness of the proposed
policy, and the optimal policy has a distinct decision boundary-switching
property, providing valuable insights for practical system design.
