  Considering a heterogeneous network (HetNet) where both macro base station
(BS) and small cell (SC) nodes are equipped with massive antennas, this paper
studies the performance for multiple-input multiple-output (MIMO) downlinks
when the macro and small cells share the same spectrum and hence interfere with
each other. Suppose that the large-scale antenna arrays at both macro BS and SC
nodes employ maximum-ratio transmission (MRT) or zero-forcing transmission
(ZFT) precoding, and transmit data streams to the served users simultaneously.
A new pilot reuse pattern among SCs is proposed for channel estimation. Taking
into account imperfect channel state information (CSI), capacity lower bounds
for MRT and ZFT are derived, respectively, in closed-form expressions involving
only statistical CSI. Then asymptotic analyses for massive arrays are presented
under specific power scaling laws. Subsequently, two user scheduling
algorithms, greedy scheduling algorithm and asymptotical scheduling algorithm
(ASA), are proposed based on derived capacity lower bounds and asymptotic
analyses, respectively. ASA is demonstrated to be a near optimal in the
asymptotic regime and has low complexity. Finally, the derived closed-form
expressions are verified to be accurate predictors of the system performance by
Monte-Carlo simulations. Numerical results demonstrate the effectiveness of
asymptotic analysis and proposed user scheduling schemes.
