  In this paper, we consider a generalized sub-array-connected (GSAC)
architecture for arbitrary radio frequency (RF) chain and antenna
configurations, where the number of RF chains connected to a sub-array and the
number of antennas in each sub-array can be arbitrary. Our design objective is
to improve the energy-efficiency of the hybrid precoder of millimeter-wave
massive multiple input multiple output (MIMO) systems. We firstly propose a
successive interference cancellation based hybrid precoding algorithm to
maximize the achievable rate for any given RF chain and antenna configuration.
This algorithm firstly decomposes the total achievable rate optimization
problem into multiple sub-rate optimization problems, then it successively
maximizes these sub-rates. Since the number of RF chains is limited, we can
afford using an exhaustive search scheme to evaluate all configurations and
identify the one having the best energy efficiency. Moreover, to rely on an
attractive limited feedback, we also propose a beamsteering codebook for our
hybrid precoding aided GSAC architecture. Our simulation results demonstrate
that the proposed scheme achieves a similar rate as the corresponding optimal
unconstrained precoder. Furthermore, we show that the energy-efficiency of the
proposed scheme is better than that of the existing schemes in the
fully-connected and sub-array-connected architectures.
