  This paper investigates the simultaneous wireless information and power
transfer (SWIPT) precoding scheme for K-user multiple-input-multiple-output
(MIMO) interference channels (IC), for which interference alignment (IA)
schemes provide optimal precoders to achieve full degrees-of-freedom (DoF)
gain. However, harvesting RF energy simultaneously reduces the achievable DoFs.
To study a trade-off between harvested energy and sum rate, the transceiver
design problem is suboptimally formulated in literature via convex relaxations,
which is still computationally intensive, especially for battery limited nodes
running on harvested energy. In this paper, we propose a systematic method
using chordal distance (CD) decomposition to obtain the balanced precoding,
which improves the trade-off. Analysis shows that given the nonnegative value
of CD, the achieved harvested energy for the proposed precoder is higher than
that for perfect IA precoder. Moreover, energy constraints can be achieved,
while maintaining a constant rate loss without losing DoFs via tuning the CD
value and splitting factor. Simulation results verify the analysis and add that
the IA schemes based on max-SINR or mean-squared error are better suited for
SWIPT maximization than subspace or leakage minimization methods.
