  This paper investigates the simultaneous wireless information and power
transfer (SWIPT) in cooperative relay networks, where a relay harvests energy
from the radio frequency (RF) signals transmitted by a source and then uses the
harvested energy to assist the information transmission from the source to its
destination. Both source and relay transmissions use rateless code, which
allows the destination to employ any of the two information receiving
strategies, i.e., the mutual information accumulation (IA) and the energy
accumulation (EA). The SWIPT-enabled relay employs three different SWIPT
receiver architectures, the ideal receiver and two practical receivers (i.e.,
the power splitting (PS) and the time switch (TS) receivers). Accordingly,
three relaying protocols, namely, ideal protocol, PS protocol and TS protocol,
are presented. In order to explore the system performance limits with these
three protocols, optimization problems are formulated to maximize their
achievable information rates. For the ideal protocol, explicit expressions of
the optimal solutions are derived. For the PS protocol, a linear-search
algorithm is designed to solve the non-convex problems. For the TS protocol,
two solving methods are presented. Numerical experiments are carried out to
validate our analysis and algorithms, which also show that, with the same SWIPT
receiver, the IA-based system outperforms the EA-based system, while with the
same information receiving strategy, PS protocol outperforms TS protocol.
Moreover, compared with conventional non-SWIPT and non-rateless-coded systems,
the proposed protocols exhibit considerable performance gains, especially in
relatively low signal-to-noise ratio (SNR) regime. Besides, the effects of the
source-destination direct link and the relay position on system performance are
also discussed, which provides insights on SWIPT-enabled relay systems.
