1 research outputs found
SWIPT using Hybrid ARQ over Time Varying Channels
We consider a class of wireless powered devices employing Hybrid Automatic
Repeat reQuest (HARQ) to ensure reliable end-to-end communications over a
two-state time-varying channel. A receiver, with no power source, relies on the
energy transferred by a Simultaneous Wireless Information and Power Transfer
(SWIPT) enabled transmitter to \emph{receive} and \emph{decode} information.
Under the two-state channel model, information is received at two different
rates while it is only possible to harvest energy in one of the states. The
receiver aims to decode its messages with minimum expected number of
re-transmissions. Dynamic and continuous nature of the problem motivated us to
use a novel Markovian framework to bypass the complexities plaguing the
conventional approaches such as MDP. Using the theory of absorbing Markov
chains, we show that there exists an optimal policy utilizing the incoming RF
signal solely to harvest energy or to accumulate mutual information. Hence, we
convert the original problem with continuous action and state space into an
equivalent one with discrete state and action space. For independent and
identically distributed channels, we prove the optimality of a
simple-to-implement {\em harvest-first-store-later} type policy. However, for
time-correlated channels, we demonstrate that statistical knowledge of the
channel may significantly improve the performance over such policies