Simultaneous Wireless Information and Power Transfer in Cooperative Relay Networks with Rateless Codes

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.