  We consider the problem of peak-to-average power ratio (PAPR) reduction for
orthogonal frequency-division multiplexing (OFDM) based large-scale
multiple-input multipleoutput (MIMO) systems. A novel perturbation-assisted
scheme is developed to reduce the PAPRs of the transmitted signals by
exploiting the redundant degrees-of-freedom (DoFs) inherent in the large-scale
antenna array. Specifically, we introduce artificial perturbation signals to
the frequency-domain precoded signals, with the aim of reducing the PAPRs of
their time-domain counterpart signals. Meanwhile, the additive perturbation
signal associated with each tone is constrained to lie in the null-space of its
associated channel matrix, such that it does not cause any multi-user inference
or out-of-band radiations. Such a problem is formulated as a convex
optimization problem, and an efficient algorithm is developed by resorting to
the variable splitting and alterative direction method of multipliers (ADMM)
techniques. Simulation results show that the proposed method has a fast
convergence rate and achieves substantial PAPR reduction within only tens of
iterations. In addition, unlike other precoding-based PAPR reduction methods,
our proposed method which introduces perturbation signals to the precoded
signals is independent of the precoding stage and thus could be more suitable
for practical systems.
