Average Age of Information in Wireless Powered Relay Aided Communication Network

In order to satisfy timeliness requirements arising from environmental sensing applications, age of information (AoI) was proposed to characterise the freshness of the received updates. In this paper, we consider a wireless powered relay aided communication network (WPRCN), in which a relay wirelessly powered by a hybrid-access point (H-AP) receives environmental monitoring information update from a sensor and forwards it to the H-AP. The long-term average AoI is studied since the decision correctness depends on the update timely uploaded by the relay. The wireless powered relay adopts either a decode-and-forward (DF) or an amplify and forward (AF) protocols, respectively, subject to the energy causality. We also consider the decoding cost of DF protocol owing to the relay’s limited energy storage. Since the expression of the average AoI is non-elementary, we propose a Taylor approximation based algorithm to obtain its integral. We optimise the transmit power/the equivalent average power consumption of the relay for the sake of minimising the average AoI in the whole WPRCN with different forwarding protocols. Our simulation results demonstrate the accuracy of the theoretical analysis, while the average AoI of the WPRCN is optimised by our power allocation scheme at the relay. The proposed algorithm is verified to achieve great approximation effect.