Timely Two-Way Data Exchanging in Unilaterally Powered Fog Computing Systems

Fog computing is attracting more and more attention to the next-generation wireless communication systems. In this paper, we consider such a mobile edge scenario where a fog node and a mobile user exchange their data in a two-way manner and only the fog node has a constant power supply. In particular, the fog node performs energy transfer when it is not transmitting information and the mobile user has an energy harvesting capability. For this scenario, we investigate the timeliness of the two-way data exchange between the fog node and the mobile user in terms of age of information (AoI) and derive closed-form average AoI for both directions, as well as the achievable data rate of the mobile user. We also discuss the achievable tradeoff on the average downlink/uplink AoIs and the achievable tradeoff on downlink/uplink data rates, which explicitly present the performance limit of the system in terms of timeliness and efficiency.