  In both academia and industry, multi-user multiple-input multiple-output
(MU-MIMO) techniques have shown enormous gains in spectral efficiency by
exploiting spatial degrees of freedom. So far, an underlying assumption in most
of the existing MU-MIMO design has been that all the users use infinite
blocklength, so that they can achieve the Shannon capacity. This setup,
however, is not suitable considering delay-constrained users whose blocklength
tends to be finite. In this paper, we consider a heterogeneous setting in
MU-MIMO systems where delay-constrained users and delay-tolerant users coexist,
called a DCTU-MIMO network. To maximize the sum spectral efficiency in this
system, we present the spectral efficiency for delay-tolerant users and provide
a lower bound of the spectral efficiency for delay-constrained users. We
consider an optimization problem that maximizes the sum spectral efficiency of
delay-tolerant users while satisfying the latency constraint of
delay-constrained users, and propose a generalized power iteration (GPI)
precoding algorithm that finds a principal precoding vector. Furthermore, we
extend a DCTU-MIMO network to the multiple time slots scenario and propose a
recursive generalized power iteration precoding algorithm. In simulation
results, we prove proposed methods outperform baseline schemes and present the
effect of network parameters on the ergodic sum spectral efficiency.
