Efficient PHY layer security in MIMO-OFDM: Spatiotemporal selective artificial noise

Beamforming and artificial noise (AN) are two major techniques to maintain physical (PHY) layer security. Using AN to degrade eavesdroppers´ signal reception enables data secrecy with less power compared to no-AN scenarios. Existing AN approaches make use of the spatial selectivity of the wireless channel however these techniques do not consider the associated signal structure. In this paper we extend the existing AN techniques to MIMO-OFDM, where we prove that the optimization problem can be inverted to a convex form in multi-antenna, multi-carrier systems, hence show that convex optimization can still be applied to preserve privacy. Furthermore, inspired by the fact that pilot symbols are critical in error-free the reception of the information symbols, we propose a spatiotemporal selective AN approach that can make use of both the space and time selectivity, as our main contribution. We also show that our proposed method can cause extensive channel estimation error for eavesdroppers and achieves significant transmission power savings at the same time.