  In this paper, we propose a novel low-complexity hybrid
linear/Tomlinson-Harashima precoder (H-L-THP) for downlink large-scale
multiuser multiple-input multiple-output (MU-MIMO) systems. The proposed
precoder comprises an inner linear precoder which utilizes only the second
order statistics of the channel state information (CSI) and outer THPs which
use the instantaneous overall CSI of the cascade of the actual channel and the
inner precoder. The user terminals are divided into groups, where for each
group a THP successively mitigates the intra-group interference, whereas the
inter-group interference is canceled by the inner linear precoder. Our
simulation results show that the bit error rate (BER) of the proposed H-L-THP
precoder is close to that of the conventional THP precoder, and is
substantially lower than the BER of the commonly used regularized zero-forcing
(RZF) precoder. Moreover, we derive exact expressions for the computational
complexity of the proposed H-L-THP precoder in terms of the required numbers of
floating-point operations. These results reveal that the proposed H-L-THP
precoder has a much lower computational complexity than the conventional THP
and RZF precoders, and is thus an excellent candidate for practical
implementations.
