  In this paper, we investigate secure transmission over the large-scale
multiple-antenna wiretap channel with finite alphabet inputs. First, we show
analytically that a generalized singular value decomposition (GSVD) based
design, which is optimal for Gaussian inputs, may exhibit a severe performance
loss for finite alphabet inputs in the high signal-to-noise ratio (SNR) regime.
In light of this, we propose a novel Per-Group-GSVD (PG-GSVD) design which can
effectively compensate the performance loss caused by the GSVD design. More
importantly, the computational complexity of the PG-GSVD design is by orders of
magnitude lower than that of the existing design for finite alphabet inputs in
[1] while the resulting performance loss is minimal. Numerical results indicate
that the proposed PG-GSVD design can be efficiently implemented in large-scale
multiple-antenna systems and achieves significant performance gains compared to
the GSVD design.
