Adding PHY-Layer Crypto to COFDM Radios through a Large Array with Directional Modulation.

Due to its ability to provide radio-transmission security at the PHY-layer, thus without relying on secret key exchange procedures and encryption algorithms, Directional modulation (DM) has recently attracted significant attention within wireless research communities. Such technique uses an antenna array as a spatial encryption system which partitions the surrounding space into regions where the transmission is either perfectly intelligible or intentionally obfuscated. This paper, which builds upon previous work from the same authors, shows how, by resorting to the proposed DM approach and accepting a slight back-off on the maximum possible array gain (typically << 1 dB for large arrays), it is possible to complement existing, state-of-art COFDM radio interfaces with PHY-layer information security by just replacing their antenna systems. Such result is obtained without actually degrading signal properties and performance within the regions being intentionally served by the DM-enabled signal. Numerical analyses as well as a real-world application of the devised system to mainstream radio standards (namely ETSI DVB-T and IEEE 802.11) are presented in support of the proposed solution.