Wireless power transfer (WPT) is a promising new
solution to provide convenient and perpetual energy supplies to
wireless networks. In practice, WPT is implementable by various
technologies such as inductive coupling, magnetic resonate
coupling, and electromagnetic (EM) radiation, for short-/mid-
/long-range applications, respectively. In this paper, we consider
the EM or radio signal enabled WPT in particular. Since radio
signals can carry energy as well as information at the same
time, a unified study on simultaneous wireless information and
power transfer (SWIPT) is pursued. Specifically, this paper studies
a multiple-input multiple-output (MIMO) wireless broadcast
system consisting of three nodes, where one receiver harvests
energy and another receiver decodes information separately from
the signals sent by a common transmitter, and all the transmitter
and receivers may be equipped with multiple antennas. Two
scenarios are examined, in which the information receiver and
energy receiver are separated and see different MIMO channels
from the transmitter, or co-located and see the identical MIMO
channel from the transmitter. For the case of separated receivers,
we derive the optimal transmission strategy to achieve different
tradeoffs for maximal information rate versus energy transfer,
which are characterized by the boundary of a so-called rateenergy