  This paper investigates the end-to-end throughput maximization problem for a
two-hop multiple-relay network, with relays powered by simultaneous wireless
information and power transfer (SWIPT) technique. Nonlinearity of energy
harvester at every relay node is taken into account and two models for
approximating the nonlinearity are adopted: logistic model and linear cut-off
model. Decode-and-forward (DF) is implemented, and time switching (TS) mode and
power splitting (PS) mode are considered. Optimization problems are formulated
for TS mode and PS mode under logistic model and linear cut-off model,
respectively. End-to-end throughput is aimed to be maximized by optimizing the
transmit power and bandwidth on every source-relay-destination link, and PS
ratio and/or TS ratio on every relay node. Although the formulated optimization
problems are all non-convex. Through a series of analysis and transformation,
and with the aid of bi-level optimization and monotonic optimization, etc., we
find the global optimal solution of every formulated optimization problem. In
some case, a simple yet optimal solution of the formulated problem is also
derived. Numerical results verify the effectiveness of our proposed methods.
