  We consider the problem of maximizing the harvested power in Multiple Input
Multiple Output (MIMO) Simultaneous Wireless Information and Power Transfer
(SWIPT) systems with power splitting reception. Different from recently
proposed designs, with our optimization problem formulation we target for the
jointly optimal transmit precoding and receive uniform power splitting (UPS)
ratio maximizing the harvested power, while ensuring that the
quality-of-service requirement of the MIMO link is satisfied. We assume
practical Radio-Frequency (RF) energy harvesting (EH) receive operation that
results in a non-convex optimization problem for the design parameters, which
we first formulate in an equivalent generalized convex problem that we then
solve optimally. We also derive the globally optimal transmit precoding design
for ideal reception. Furthermore, we present analytical bounds for the key
variables of both considered problems along with tight high signal-to-noise
ratio approximations for their optimal solutions. Two algorithms for the
efficient computation of the globally optimal designs are outlined. The first
requires solving a small number of non-linear equations, while the second is
based on a two-dimensional search having linear complexity. Computer simulation
results are presented validating the proposed analysis, providing key insights
on various system parameters, and investigating the achievable EH gains over
benchmark schemes.
