Physical-layer security for multi-antenna wiretap channel in the wideband regime

Perfect security for the multi-antenna wiretap channel is considered, at the physical layer, under a limited-energy constraint. The problem was originally considered in [1] for point-to-point channels, where the fundamental limits of secure communication have been established in the wideband regime. In this paper, the more general multi-antenna scenario is addressed. The main result proves that the secrecy capacity per unit cost (energy), under the mild condition of zero-cost input letter, can be achieved using a structured orthogonal random binning coding scheme.