  For the practical implementation of massive multiple-input multiple-output
(MIMO) systems, the hybrid processing (precoding/combining) structure is
promising to reduce the high cost rendered by large number of RF chains of the
traditional processing structure. The hybrid processing is performed through
low-dimensional digital baseband processing combined with analog RF processing
enabled by phase shifters. We propose to design hybrid RF and baseband
precoders/combiners for multi-stream transmission in point-to-point massive
MIMO systems, by directly decomposing the pre-designed unconstrained digital
precoder/combiner of a large dimension. The constant amplitude constraint of
analog RF processing results in the matrix decomposition problem non-convex.
Based on an alternate optimization technique, the non-convex matrix
decomposition problem can be decoupled into a series of convex sub-problems and
effectively solved by restricting the phase increment of each entry in the RF
precoder/combiner within a small vicinity of its preceding iterate. A singular
value decomposition based technique is proposed to secure an initial point
sufficiently close to the global solution of the original non-convex problem.
Through simulation, the convergence of the alternate optimization for such a
matrix decomposition based hybrid processing (MD-HP) scheme is examined, and
the performance of the MD-HP scheme is demonstrated to be near-optimal.
