  Fog devices are beginning to play a key role in relaying data and services
within the Internet-of-Things (IoT) ecosystem. These relays may be static or
mobile, with the latter offering a new degree of freedom for performance
improvement via careful relay mobility design. Besides that, power conservation
has been a prevalent issue in IoT networks with devices being
power-constrained, requiring optimal power-control mechanisms. In this paper,
we consider a multi-tier fog-based IoT architecture where a mobile/static fog
node acts as an amplify and forward relay that transmits received information
from a sensor node to a higher hierarchically-placed static fog device, which
offers some localized services. The outage probability of the presented
scenario was efficiently minimized by jointly optimizing the mobility pattern
and the transmit power of the fog relay. A closed-form analytical expression
for the outage probability was derived. Furthermore, due to the intractability
and non-convexity of the formulated problem, we applied an iterative algorithm
based on the steepest descent method to arrive at a desirable objective.
Simulations reveal that the outage probability was improved by 62.7% in the
optimized-location fixed-power (OLFP) scheme, 79.3% in the optimized-power
fixed-location (OPFL) scheme, and 94.2% in the optimized-location
optimized-power (OLOP) scheme, as against the fixed-location and fixed-power
(FLFP) scheme (i.e., without optimization). Lastly, we present an optimal relay
selection strategy that chooses an appropriate relay node from randomly
distributed relaying candidates.
