  In this paper, we consider a fog computing system consisting of a
multi-antenna access point (AP), an ultra-low power (ULP) single antenna device
and a fog server. The ULP device is assumed to be capable of both energy
harvesting (EH) and information decoding (ID) using a time-switching
simultaneous wireless information and power transfer (SWIPT) scheme. The ULP
device deploys the harvested energy for ID and either local computing or
offloading the computations to the fog server depending on which strategy is
most energy efficient. In this scenario, we optimize the time slots devoted to
EH, ID and local computation as well as the time slot and power required for
the offloading to minimize the energy cost of the ULP device. Numerical results
are provided to study the effectiveness of the optimized fog computing system
and the relevant challenges.
